Upper/Lower Limb — MCQs

Q: A patient with a nerve injury was asked to form an "O" with their index finger and thumb but was unable to do so. Which muscle is most likely affected?

Opponens pollicis. ***Opponens pollicis*** - The **opponens pollicis** muscle is responsible for **opposition of the thumb**, a complex movement involving flexion, abduction, and medial rotation of the thumb at the carpometacarpal joint. - Inability to form an "O" sign with the index finger and thumb is a classic clinical test for impaired opposition, often indicating a problem with the **median nerve** or the opponens pollicis muscle it innervates. *Abductor pollicis brevis* - The **abductor pollicis brevis** primarily abducts the thumb, moving it away from the palm. - While necessary for thumb function, its primary role is not the opposition motion required to touch the fingertips in an "O" shape. *Flexor pollicis brevis* - The **flexor pollicis brevis** primarily flexes the thumb at the metacarpophalangeal joint. - While it contributes to thumb movements, it is not the primary muscle responsible for the complex motion of opposition. *Adductor pollicis* - The **adductor pollicis** adducts the thumb, bringing it towards the palm and index finger. - Innervated by the **ulnar nerve**, this muscle is important for pinch grip but is not the primary muscle for opposition movement. *Palmar interossei* - The **palmar interossei** muscles adduct the fingers, pulling them towards the middle finger. - These muscles are involved in finger adduction, not direct thumb opposition, and are typically innervated by the ulnar nerve.

Q: A patient diagnosed with sciatica has tender hamstrings. Which of the following nerves supplies a hybrid muscle that is partially spared in this patient?

Common peroneal nerve. ***Common peroneal nerve*** - The **short head of the biceps femoris** is a unique "hybrid" muscle, supplied by the **common peroneal nerve**, while the **long head** is supplied by the **tibial nerve**. - If the hamstrings are tender and sciatica is present, but this specific muscle's function is spared, it points towards the common peroneal nerve being the relevant nerve for the spared portion. *Femoral* - The **femoral nerve** primarily innervates the **anterior compartment of the thigh**, including the quadriceps femoris. - It does not supply any part of the hamstring muscles. *Obturator* - The **obturator nerve** primarily innervates the **medial compartment of the thigh**, which consists of adductor muscles. - It does not contribute to the innervation of the hamstring muscles. *Superior gluteal* - The **superior gluteal nerve** innervates the **gluteus medius**, **gluteus minimus**, and **tensor fasciae latae** muscles. - It does not supply any hamstring muscles. *Tibial* - The **tibial nerve** innervates most of the hamstring muscles (semitendinosus, semimembranosus, and the long head of the biceps femoris). - If the hamstrings are tender, involvement of the tibial nerve would likely lead to more widespread hamstring weakness rather than a partially spared scenario involving the short head of the biceps femoris.

Q: Which artery is palpated behind the medial malleolus and in front of the Achilles tendon?

Posterior tibial artery. ***Posterior tibial artery*** - This artery is directly accessible for palpation in the **retromalleolar groove**, situated between the medial malleolus and the Achilles tendon. - It is a common site for assessing **peripheral circulation** in the foot. *Peroneal artery* - The peroneal artery is located **deep within the posterior compartment** of the leg, making it difficult to palpate at the ankle. - It primarily supplies the lateral compartment and is not typically palpable at the described location. *Anterior tibial artery* - The anterior tibial artery runs along the **anterior compartment** of the lower leg and, at the ankle, becomes the dorsalis pedis artery. - It is best palpated on the **dorsum of the foot** as the dorsalis pedis artery, not behind the medial malleolus. *Dorsalis pedis artery* - This artery is a continuation of the anterior tibial artery and is found on the **dorsum of the foot**, typically lateral to the extensor hallucis longus tendon. - While an important pulse point, it is not located behind the medial malleolus. *Popliteal artery* - The popliteal artery is located in the **popliteal fossa** behind the knee, where it can be palpated with deep pressure. - It is proximal to the ankle and divides into the anterior and posterior tibial arteries, making it anatomically distant from the medial malleolus.

Q: A patient presents with pain in the back of the thigh and leg after lifting heavy weights. Which spinal segment is most likely involved?

S1. ***S1*** - Pain radiating to the **back of the thigh and leg** after lifting heavy weights is the classic presentation of **S1 radiculopathy**, typically from L5-S1 disc herniation. - The S1 nerve root innervates the **posterior thigh via the sciatic nerve**, continues down the **posterior leg**, and extends to the **lateral foot and little toe**. - Clinical findings include diminished or absent **Achilles reflex**, weakness of **plantar flexion** (gastrocnemius/soleus), and sensory changes along the posterior leg and lateral foot. - This is the **most common** presentation of sciatica from heavy lifting. *L3* - L3 nerve root involvement typically causes pain in the **anterior and medial thigh** with weakness of **hip flexion and knee extension** (quadriceps). - The pain pattern does not match the posterior distribution described in this clinical scenario. *L4* - L4 radiculopathy presents with pain and numbness in the **medial leg and foot**, weakness of **ankle dorsiflexion** (tibialis anterior), and diminished **patellar reflex**. - The pain distribution is anteromedial, not posterior as described in this case. *L5* - L5 nerve root impingement causes pain radiating to the **lateral calf and dorsum of the foot**, weakness of **great toe extension** (extensor hallucis longus), and **foot drop**. - While L5 can cause posterior thigh pain, the classic distribution extends laterally down the leg, not primarily posterior. *S2* - S2 radiculopathy is uncommon and typically presents with **perineal/perianal pain** and **saddle anesthesia** rather than isolated posterior leg pain. - S2 contributes to bladder and bowel function; isolated S2 involvement would not present with the classic sciatica pattern described.

Q: A patient underwent a coronary artery bypass graft (CABG) using the great saphenous vein. Post-surgery, the patient experiences neuralgia on the medial aspect of the leg and foot. Which nerve is most likely injured?

Saphenous nerve. ***Saphenous nerve*** - The **saphenous nerve** is a cutaneous branch of the femoral nerve that runs closely with the **great saphenous vein** along the medial aspect of the leg and foot. - Due to its proximity to the vein, it is highly susceptible to **injury** during the harvesting of the great saphenous vein for CABG, leading to **neuralgia** in its sensory distribution. *Common peroneal nerve* - The **common peroneal nerve** innervates the lateral and anterior compartments of the leg, affecting dorsiflexion and eversion of the foot. - Damage to this nerve typically results in **foot drop** and sensory loss over the dorsum of the foot, which is inconsistent with the patient's symptoms. *Tibial nerve* - The **tibial nerve** supplies the posterior compartment of the leg and the plantar aspect of the foot. - Injury would cause loss of plantarflexion and sensation on the sole of the foot, which is not described. *Sural nerve* - The **sural nerve** provides sensation to the posterolateral aspect of the leg and the lateral side of the foot and ankle. - While it runs near superficial veins, its sensory distribution does not match the described **medial leg and foot neuralgia**. *Superficial peroneal nerve* - The **superficial peroneal nerve** (superficial fibular nerve) provides sensation to the dorsum of the foot and anterolateral leg. - Injury would cause sensory loss over the dorsal foot, not the medial aspect of the leg and foot.

Q: A young boy presents with multiple humerus fractures, resulting in loss of sensation over the lateral side of the forearm, along with difficulty in elbow flexion and forearm supination. What is the most likely nerve injury responsible for these symptoms?

Musculocutaneous nerve. ***Musculocutaneous nerve*** - The **musculocutaneous nerve** innervates the biceps brachii and brachialis muscles, responsible for **elbow flexion** and **forearm supination**, and provides sensation to the **lateral forearm** via the lateral cutaneous nerve of the forearm. - A fracture of the humerus can damage this nerve, leading to the observed **motor and sensory deficits**. *Median nerve* - The median nerve primarily controls **flexion of the wrist and fingers**, and **pronation of the forearm**, as well as sensation to the palmar aspect of the thumb, index, middle, and radial half of the ring finger. - Its injury would not typically cause difficulty with **elbow flexion** or sensory loss over the **lateral forearm**. *Axillary* - The axillary nerve primarily innervates the **deltoid** and **teres minor muscles**, important for shoulder abduction and external rotation. - An injury would lead to **weakness in shoulder abduction** and sensory loss over the lateral shoulder (regimental badge area), not the lateral forearm. *Radial nerve* - The radial nerve controls **extension of the wrist and fingers** and sensation over the posterior arm, forearm, and hand. - Injury typically results in **wrist drop** and difficulty extending the arm, not primarily elbow flexion or lateral forearm sensation. *Ulnar nerve* - The ulnar nerve innervates intrinsic hand muscles and flexor carpi ulnaris, controlling **finger abduction/adduction** and **ulnar wrist flexion**. - Sensory distribution includes the medial hand and medial 1.5 fingers, not the **lateral forearm**. - Injury causes **claw hand deformity** and sensory loss in the medial hand, not the symptoms described.

Q: A 32-year-old man comes to the physician because of episodic tingling and numbness in his right hand for the past 3 months. His symptoms are worse in the evening. There is no history of trauma. He is employed as a carpenter. He has smoked 1 pack of cigarettes daily for the past 10 years. He drinks a pint of vodka daily. He does not use illicit drugs. His vital signs are within normal limits. Physical examination shows decreased pinch strength in the right hand. Sensations are decreased over the little finger and both the dorsal and palmar surfaces of the medial aspect of the right hand. Which of the following is the most likely site of nerve compression?

Cubital tunnel. ***Cubital tunnel*** - Compression of the **ulnar nerve** at the cubital tunnel typically presents with paresthesias and numbness in the **little finger** and medial half of the ring finger, along with weakness in **intrinsic hand muscles** (decreased pinch strength). - The carpenter's occupation may involve repetitive elbow flexion, exacerbating **ulnar nerve compression** at the elbow. *Guyon canal* - Compression in the **Guyon canal** affects the **ulnar nerve** at the wrist. - While it can cause similar sensory and motor deficits in the hand, the cubital tunnel is a more common site of compression for the ulnar nerve, and symptoms worsen with **elbow flexion**. *Carpal tunnel* - **Carpal tunnel syndrome** involves compression of the **median nerve** and causes numbness and tingling in the thumb, index, middle, and radial half of the ring finger, sparing the little finger. - It does not cause decreased sensation over the **little finger**. *Quadrilateral space* - **Quadrilateral space syndrome** involves compression of the **axillary nerve** and presents with shoulder pain, paresthesias over the lateral shoulder, and weakness in abduction and external rotation. - This does not align with the patient's hand symptoms. *Radial groove* - Compression of the **radial nerve** in the radial groove (spiral groove) of the humerus typically results in **wrist drop**, weakness in forearm and hand extensors, and sensory loss over the dorsum of the hand, not the ulnar distribution described. - This is not consistent with the patient's sensory and motor deficits.

Q: A 56-year-old man comes to the emergency department because of pain and swelling in his left leg. He has a history of pancreatic cancer and is currently receiving chemotherapy. Three weeks ago, he had a similar episode in his right arm that resolved without treatment. His temperature is 38.2°C (100.8°F). Palpation of the left leg shows a tender, cord-shaped structure medial to the medial condyle of the femur. The overlying skin is erythematous. Which of the following vessels is most likely affected?

Great saphenous vein. ***Great saphenous vein*** - The description of a **tender, cord-shaped structure** with overlying **erythema** medial to the medial condyle is classic for **superficial thrombophlebitis** affecting the great saphenous vein. - The history of **pancreatic cancer** and recurrent migratory thrombophlebitis (similar episode in the right arm) points towards **Trousseau's sign**, which is often associated with malignancy. *Superficial femoral artery* - An affected artery would typically present with symptoms of **ischemia**, such as **pain, pallor, pulselessness, paresthesia, and paralysis**, rather than a tender, cord-like structure. - While it runs in the thigh, its location deep within the adductor canal and its arterial nature make it an unlikely candidate for the described superficial signs. *External iliac vein* - This vein is located deep within the pelvis and upper thigh, making it impossible to palpate superficially as a "cord-shaped structure." - Thrombosis here would typically cause significant **limb swelling** and potentially a **deep venous thrombosis (DVT)**, not superficial thrombophlebitis. *Anterior tibial artery* - This artery is located in the anterior compartment of the lower leg, supplying the foot, and runs deep. - Involvement would cause **distal ischemia** and not present as a palpable cord medial to the medial condyle of the femur. *Deep femoral vein* - As a deep vein, it would not manifest as a superficial, palpable cord and is a common site for DVT. - Thrombosis in this vein would typically cause more diffuse swelling of the upper thigh and would not be associated with a superficial erythematous cord.

A 45-year-old woman presents to her primary care provider for wrist pain. She reports a 4-month history of gradually worsening pain localized to the radial side of her right wrist. The pain is dull, non-radiating, and intermittent. Her past medical history is notable for rheumatoid arthritis and von Willebrand disease. She does not smoke and drinks alcohol socially. She is active in her neighborhood’s local badminton league. Her temperature is 98.6°F (37°C), blood pressure is 125/75 mmHg, pulse is 80/min, and respirations are 18/min. On exam, she has mild tenderness to palpation in her thenar snuffbox. Nodules are located on the proximal interphalangeal joints of both hands. Ulnar deviation of the hand with her thumb clenched in her palm produces pain. Which of the following muscles in most likely affected in this patient?

A 32-year-old man comes to the physician because of episodic tingling and numbness in his right hand for the past 3 months. His symptoms are worse in the evening. There is no history of trauma. He is employed as a carpenter. He has smoked 1 pack of cigarettes daily for the past 10 years. He drinks a pint of vodka daily. He does not use illicit drugs. His vital signs are within normal limits. Physical examination shows decreased pinch strength in the right hand. Sensations are decreased over the little finger and both the dorsal and palmar surfaces of the medial aspect of the right hand. Which of the following is the most likely site of nerve compression?

Q10

A 56-year-old man comes to the emergency department because of pain and swelling in his left leg. He has a history of pancreatic cancer and is currently receiving chemotherapy. Three weeks ago, he had a similar episode in his right arm that resolved without treatment. His temperature is 38.2°C (100.8°F). Palpation of the left leg shows a tender, cord-shaped structure medial to the medial condyle of the femur. The overlying skin is erythematous. Which of the following vessels is most likely affected?

Upper/Lower Limb US Medical PG Practice Questions and MCQs

Question 1: A patient with a nerve injury was asked to form an "O" with their index finger and thumb but was unable to do so. Which muscle is most likely affected?

A. Opponens pollicis (Correct Answer)
B. Abductor pollicis brevis
C. Flexor pollicis brevis
D. Palmar interossei
E. Adductor pollicis

Explanation: ***Opponens pollicis*** - The **opponens pollicis** muscle is responsible for **opposition of the thumb**, a complex movement involving flexion, abduction, and medial rotation of the thumb at the carpometacarpal joint. - Inability to form an "O" sign with the index finger and thumb is a classic clinical test for impaired opposition, often indicating a problem with the **median nerve** or the opponens pollicis muscle it innervates. *Abductor pollicis brevis* - The **abductor pollicis brevis** primarily abducts the thumb, moving it away from the palm. - While necessary for thumb function, its primary role is not the opposition motion required to touch the fingertips in an "O" shape. *Flexor pollicis brevis* - The **flexor pollicis brevis** primarily flexes the thumb at the metacarpophalangeal joint. - While it contributes to thumb movements, it is not the primary muscle responsible for the complex motion of opposition. *Adductor pollicis* - The **adductor pollicis** adducts the thumb, bringing it towards the palm and index finger. - Innervated by the **ulnar nerve**, this muscle is important for pinch grip but is not the primary muscle for opposition movement. *Palmar interossei* - The **palmar interossei** muscles adduct the fingers, pulling them towards the middle finger. - These muscles are involved in finger adduction, not direct thumb opposition, and are typically innervated by the ulnar nerve.

Question 2: A patient diagnosed with sciatica has tender hamstrings. Which of the following nerves supplies a hybrid muscle that is partially spared in this patient?

A. Femoral
B. Common peroneal nerve (Correct Answer)
C. Obturator
D. Tibial
E. Superior gluteal

Explanation: ***Common peroneal nerve*** - The **short head of the biceps femoris** is a unique "hybrid" muscle, supplied by the **common peroneal nerve**, while the **long head** is supplied by the **tibial nerve**. - If the hamstrings are tender and sciatica is present, but this specific muscle's function is spared, it points towards the common peroneal nerve being the relevant nerve for the spared portion. *Femoral* - The **femoral nerve** primarily innervates the **anterior compartment of the thigh**, including the quadriceps femoris. - It does not supply any part of the hamstring muscles. *Obturator* - The **obturator nerve** primarily innervates the **medial compartment of the thigh**, which consists of adductor muscles. - It does not contribute to the innervation of the hamstring muscles. *Superior gluteal* - The **superior gluteal nerve** innervates the **gluteus medius**, **gluteus minimus**, and **tensor fasciae latae** muscles. - It does not supply any hamstring muscles. *Tibial* - The **tibial nerve** innervates most of the hamstring muscles (semitendinosus, semimembranosus, and the long head of the biceps femoris). - If the hamstrings are tender, involvement of the tibial nerve would likely lead to more widespread hamstring weakness rather than a partially spared scenario involving the short head of the biceps femoris.

Question 3: Which artery is palpated behind the medial malleolus and in front of the Achilles tendon?

A. Peroneal artery
B. Anterior tibial artery
C. Dorsalis pedis artery
D. Posterior tibial artery (Correct Answer)
E. Popliteal artery

Explanation: ***Posterior tibial artery*** - This artery is directly accessible for palpation in the **retromalleolar groove**, situated between the medial malleolus and the Achilles tendon. - It is a common site for assessing **peripheral circulation** in the foot. *Peroneal artery* - The peroneal artery is located **deep within the posterior compartment** of the leg, making it difficult to palpate at the ankle. - It primarily supplies the lateral compartment and is not typically palpable at the described location. *Anterior tibial artery* - The anterior tibial artery runs along the **anterior compartment** of the lower leg and, at the ankle, becomes the dorsalis pedis artery. - It is best palpated on the **dorsum of the foot** as the dorsalis pedis artery, not behind the medial malleolus. *Dorsalis pedis artery* - This artery is a continuation of the anterior tibial artery and is found on the **dorsum of the foot**, typically lateral to the extensor hallucis longus tendon. - While an important pulse point, it is not located behind the medial malleolus. *Popliteal artery* - The popliteal artery is located in the **popliteal fossa** behind the knee, where it can be palpated with deep pressure. - It is proximal to the ankle and divides into the anterior and posterior tibial arteries, making it anatomically distant from the medial malleolus.

Question 4: A patient presents with pain in the back of the thigh and leg after lifting heavy weights. Which spinal segment is most likely involved?

A. L4
B. L5
C. S1 (Correct Answer)
D. S2
E. L3

Explanation: ***S1*** - Pain radiating to the **back of the thigh and leg** after lifting heavy weights is the classic presentation of **S1 radiculopathy**, typically from L5-S1 disc herniation. - The S1 nerve root innervates the **posterior thigh via the sciatic nerve**, continues down the **posterior leg**, and extends to the **lateral foot and little toe**. - Clinical findings include diminished or absent **Achilles reflex**, weakness of **plantar flexion** (gastrocnemius/soleus), and sensory changes along the posterior leg and lateral foot. - This is the **most common** presentation of sciatica from heavy lifting. *L3* - L3 nerve root involvement typically causes pain in the **anterior and medial thigh** with weakness of **hip flexion and knee extension** (quadriceps). - The pain pattern does not match the posterior distribution described in this clinical scenario. *L4* - L4 radiculopathy presents with pain and numbness in the **medial leg and foot**, weakness of **ankle dorsiflexion** (tibialis anterior), and diminished **patellar reflex**. - The pain distribution is anteromedial, not posterior as described in this case. *L5* - L5 nerve root impingement causes pain radiating to the **lateral calf and dorsum of the foot**, weakness of **great toe extension** (extensor hallucis longus), and **foot drop**. - While L5 can cause posterior thigh pain, the classic distribution extends laterally down the leg, not primarily posterior. *S2* - S2 radiculopathy is uncommon and typically presents with **perineal/perianal pain** and **saddle anesthesia** rather than isolated posterior leg pain. - S2 contributes to bladder and bowel function; isolated S2 involvement would not present with the classic sciatica pattern described.

Question 5: The "O sign" formed by the thumb and index finger is affected. Which muscle is most likely injured?

A. Opponens pollicis
B. Flexor pollicis longus (Correct Answer)
C. Flexor pollicis brevis
D. Abductor pollicis brevis
E. Flexor digitorum profundus (index finger)

Explanation: ***Flexor pollicis longus*** - The **"O sign"** (or **"OK sign"**) tests the ability to form a tight **tip-to-tip pinch** between the thumb and index finger, creating a circular "O" shape. - This requires **flexion of the thumb interphalangeal (IP) joint** via the **flexor pollicis longus (FPL)** and **flexion of the index finger distal interphalangeal (DIP) joint** via the **flexor digitorum profundus (FDP)**. - Both FPL and FDP to the index/middle fingers are innervated by the **anterior interosseous nerve (AIN)**, a branch of the median nerve. - **AIN palsy** results in inability to flex the thumb IP and index DIP joints, causing the **"O sign"** to become flattened (pinch sign or **"teardrop sign"**). - Injury to **FPL** specifically impairs thumb IP flexion, directly affecting the ability to form the **"O sign"**. *Flexor digitorum profundus (index finger)* - The **FDP to the index finger** is also innervated by the **AIN** and is essential for flexing the DIP joint of the index finger. - Isolated FDP injury would affect the index finger's contribution to the "O sign" but both FPL and FDP are typically affected together in AIN palsy. - This is a plausible answer, making this a higher-order question testing understanding of the anatomy. *Opponens pollicis* - The **opponens pollicis** enables **opposition** of the thumb, bringing the thumb pad to the finger pads (pad-to-pad pinch). - It is innervated by the **recurrent branch of the median nerve**, not the AIN. - Opposition is different from the **tip-to-tip pinch** required for the "O sign," which requires IP joint flexion, not just opposition at the carpometacarpal joint. *Flexor pollicis brevis* - The **flexor pollicis brevis** flexes the thumb at the **metacarpophalangeal (MCP) joint**, not the IP joint. - The superficial head is innervated by the recurrent branch of the median nerve, while the deep head is innervated by the ulnar nerve. - While it contributes to thumb flexion, it does not flex the thumb IP joint, which is essential for forming the **"O sign"**. *Abductor pollicis brevis* - The **abductor pollicis brevis** abducts the thumb away from the palm in a plane perpendicular to the palm. - It is innervated by the **recurrent branch of the median nerve**. - Abduction is not required for forming the **"O sign"**, which primarily tests flexion at the IP and DIP joints.

Question 6: A patient underwent a coronary artery bypass graft (CABG) using the great saphenous vein. Post-surgery, the patient experiences neuralgia on the medial aspect of the leg and foot. Which nerve is most likely injured?

A. Common peroneal nerve
B. Sural nerve
C. Tibial nerve
D. Saphenous nerve (Correct Answer)
E. Superficial peroneal nerve

Explanation: ***Saphenous nerve*** - The **saphenous nerve** is a cutaneous branch of the femoral nerve that runs closely with the **great saphenous vein** along the medial aspect of the leg and foot. - Due to its proximity to the vein, it is highly susceptible to **injury** during the harvesting of the great saphenous vein for CABG, leading to **neuralgia** in its sensory distribution. *Common peroneal nerve* - The **common peroneal nerve** innervates the lateral and anterior compartments of the leg, affecting dorsiflexion and eversion of the foot. - Damage to this nerve typically results in **foot drop** and sensory loss over the dorsum of the foot, which is inconsistent with the patient's symptoms. *Tibial nerve* - The **tibial nerve** supplies the posterior compartment of the leg and the plantar aspect of the foot. - Injury would cause loss of plantarflexion and sensation on the sole of the foot, which is not described. *Sural nerve* - The **sural nerve** provides sensation to the posterolateral aspect of the leg and the lateral side of the foot and ankle. - While it runs near superficial veins, its sensory distribution does not match the described **medial leg and foot neuralgia**. *Superficial peroneal nerve* - The **superficial peroneal nerve** (superficial fibular nerve) provides sensation to the dorsum of the foot and anterolateral leg. - Injury would cause sensory loss over the dorsal foot, not the medial aspect of the leg and foot.

Question 7: A young boy presents with multiple humerus fractures, resulting in loss of sensation over the lateral side of the forearm, along with difficulty in elbow flexion and forearm supination. What is the most likely nerve injury responsible for these symptoms?

A. Median nerve
B. Axillary
C. Radial nerve
D. Musculocutaneous nerve (Correct Answer)
E. Ulnar nerve

Explanation: ***Musculocutaneous nerve*** - The **musculocutaneous nerve** innervates the biceps brachii and brachialis muscles, responsible for **elbow flexion** and **forearm supination**, and provides sensation to the **lateral forearm** via the lateral cutaneous nerve of the forearm. - A fracture of the humerus can damage this nerve, leading to the observed **motor and sensory deficits**. *Median nerve* - The median nerve primarily controls **flexion of the wrist and fingers**, and **pronation of the forearm**, as well as sensation to the palmar aspect of the thumb, index, middle, and radial half of the ring finger. - Its injury would not typically cause difficulty with **elbow flexion** or sensory loss over the **lateral forearm**. *Axillary* - The axillary nerve primarily innervates the **deltoid** and **teres minor muscles**, important for shoulder abduction and external rotation. - An injury would lead to **weakness in shoulder abduction** and sensory loss over the lateral shoulder (regimental badge area), not the lateral forearm. *Radial nerve* - The radial nerve controls **extension of the wrist and fingers** and sensation over the posterior arm, forearm, and hand. - Injury typically results in **wrist drop** and difficulty extending the arm, not primarily elbow flexion or lateral forearm sensation. *Ulnar nerve* - The ulnar nerve innervates intrinsic hand muscles and flexor carpi ulnaris, controlling **finger abduction/adduction** and **ulnar wrist flexion**. - Sensory distribution includes the medial hand and medial 1.5 fingers, not the **lateral forearm**. - Injury causes **claw hand deformity** and sensory loss in the medial hand, not the symptoms described.

Question 8: A 45-year-old woman presents to her primary care provider for wrist pain. She reports a 4-month history of gradually worsening pain localized to the radial side of her right wrist. The pain is dull, non-radiating, and intermittent. Her past medical history is notable for rheumatoid arthritis and von Willebrand disease. She does not smoke and drinks alcohol socially. She is active in her neighborhood’s local badminton league. Her temperature is 98.6°F (37°C), blood pressure is 125/75 mmHg, pulse is 80/min, and respirations are 18/min. On exam, she has mild tenderness to palpation in her thenar snuffbox. Nodules are located on the proximal interphalangeal joints of both hands. Ulnar deviation of the hand with her thumb clenched in her palm produces pain. Which of the following muscles in most likely affected in this patient?

A. Abductor pollicis longus (Correct Answer)
B. Extensor pollicis brevis
C. Flexor pollicis longus
D. Opponens pollicis
E. Adductor pollicis

Explanation: ***Abductor pollicis longus*** - The symptoms, particularly **pain in the radial wrist** exacerbated by **ulnar deviation of the hand with the thumb clenched in the palm** (a positive **Finkelstein's test**), are classic for **De Quervain's tenosynovitis**. - **De Quervain's tenosynovitis** specifically affects the tendons within the **first dorsal compartment of the wrist**, which contains the **abductor pollicis longus** and **extensor pollicis brevis** tendons. - The **abductor pollicis longus is the PRIMARY and MOST COMMONLY affected muscle** in De Quervain's tenosynovitis, as it is the larger tendon and bears greater mechanical stress from repetitive thumb and wrist movements (such as in badminton). - While both tendons share the same synovial sheath and can be inflamed, **APL is considered the principal muscle affected** in this condition. *Extensor pollicis brevis* - This muscle is also involved in **De Quervain's tenosynovitis** alongside the **abductor pollicis longus**, as both tendons share the same synovial sheath in the first dorsal compartment. - However, the **abductor pollicis longus is more commonly and primarily affected**, making it the better answer when asked which muscle is "most likely" involved. - In some cases, EPB may not be involved at all, whereas APL is consistently affected. *Flexor pollicis longus* - This muscle is located on the **volar (palm side)** aspect of the forearm and hand and is primarily responsible for **flexion of the thumb's interphalangeal joint**. - Involvement of this muscle would present with pain on the palmar side of the wrist or thumb, and potentially **trigger thumb**, not radial-sided wrist pain with positive Finkelstein's test. *Opponens pollicis* - This muscle is located deep in the thenar eminence and is responsible for **opposition of the thumb**, bringing it across the palm to touch other fingers. - Isolated injury or inflammation of the **opponens pollicis** would typically cause pain and weakness with thumb opposition, not the characteristic radial wrist pain with positive Finkelstein's test. *Adductor pollicis* - This muscle is responsible for **adduction of the thumb**, pulling it towards the palm, and is located in the intrinsic muscles of the hand. - Pain related to the **adductor pollicis** would be felt more deeply in the thenar web space or palm, and would not be exacerbated by the Finkelstein maneuver eliciting radial wrist pain.

Question 9: A 32-year-old man comes to the physician because of episodic tingling and numbness in his right hand for the past 3 months. His symptoms are worse in the evening. There is no history of trauma. He is employed as a carpenter. He has smoked 1 pack of cigarettes daily for the past 10 years. He drinks a pint of vodka daily. He does not use illicit drugs. His vital signs are within normal limits. Physical examination shows decreased pinch strength in the right hand. Sensations are decreased over the little finger and both the dorsal and palmar surfaces of the medial aspect of the right hand. Which of the following is the most likely site of nerve compression?

A. Guyon canal
B. Quadrilateral space
C. Carpal tunnel
D. Cubital tunnel (Correct Answer)
E. Radial groove

Explanation: ***Cubital tunnel*** - Compression of the **ulnar nerve** at the cubital tunnel typically presents with paresthesias and numbness in the **little finger** and medial half of the ring finger, along with weakness in **intrinsic hand muscles** (decreased pinch strength). - The carpenter's occupation may involve repetitive elbow flexion, exacerbating **ulnar nerve compression** at the elbow. *Guyon canal* - Compression in the **Guyon canal** affects the **ulnar nerve** at the wrist. - While it can cause similar sensory and motor deficits in the hand, the cubital tunnel is a more common site of compression for the ulnar nerve, and symptoms worsen with **elbow flexion**. *Carpal tunnel* - **Carpal tunnel syndrome** involves compression of the **median nerve** and causes numbness and tingling in the thumb, index, middle, and radial half of the ring finger, sparing the little finger. - It does not cause decreased sensation over the **little finger**. *Quadrilateral space* - **Quadrilateral space syndrome** involves compression of the **axillary nerve** and presents with shoulder pain, paresthesias over the lateral shoulder, and weakness in abduction and external rotation. - This does not align with the patient's hand symptoms. *Radial groove* - Compression of the **radial nerve** in the radial groove (spiral groove) of the humerus typically results in **wrist drop**, weakness in forearm and hand extensors, and sensory loss over the dorsum of the hand, not the ulnar distribution described. - This is not consistent with the patient's sensory and motor deficits.

Question 10: A 56-year-old man comes to the emergency department because of pain and swelling in his left leg. He has a history of pancreatic cancer and is currently receiving chemotherapy. Three weeks ago, he had a similar episode in his right arm that resolved without treatment. His temperature is 38.2°C (100.8°F). Palpation of the left leg shows a tender, cord-shaped structure medial to the medial condyle of the femur. The overlying skin is erythematous. Which of the following vessels is most likely affected?

A. Superficial femoral artery
B. External iliac vein
C. Anterior tibial artery
D. Great saphenous vein (Correct Answer)
E. Deep femoral vein

Explanation: ***Great saphenous vein*** - The description of a **tender, cord-shaped structure** with overlying **erythema** medial to the medial condyle is classic for **superficial thrombophlebitis** affecting the great saphenous vein. - The history of **pancreatic cancer** and recurrent migratory thrombophlebitis (similar episode in the right arm) points towards **Trousseau's sign**, which is often associated with malignancy. *Superficial femoral artery* - An affected artery would typically present with symptoms of **ischemia**, such as **pain, pallor, pulselessness, paresthesia, and paralysis**, rather than a tender, cord-like structure. - While it runs in the thigh, its location deep within the adductor canal and its arterial nature make it an unlikely candidate for the described superficial signs. *External iliac vein* - This vein is located deep within the pelvis and upper thigh, making it impossible to palpate superficially as a "cord-shaped structure." - Thrombosis here would typically cause significant **limb swelling** and potentially a **deep venous thrombosis (DVT)**, not superficial thrombophlebitis. *Anterior tibial artery* - This artery is located in the anterior compartment of the lower leg, supplying the foot, and runs deep. - Involvement would cause **distal ischemia** and not present as a palpable cord medial to the medial condyle of the femur. *Deep femoral vein* - As a deep vein, it would not manifest as a superficial, palpable cord and is a common site for DVT. - Thrombosis in this vein would typically cause more diffuse swelling of the upper thigh and would not be associated with a superficial erythematous cord.

Question 11: A 64-year-old female with a long-standing history of poorly-controlled diabetes presents with 3 weeks of abnormal walking. She says that lately she has noticed that she keeps dragging the toes of her right foot while walking, and this has led to her stubbing her toes. Upon physical exam, you notice a right unilateral foot drop that is accompanied by decreased sensation in the first dorsal web space. She also walks with a pronounced steppage gait. A deficit in which of the following nerves is likely responsible for this presentation?

A. Superficial peroneal nerve
B. Saphenous nerve
C. Sural nerve
D. Tibial nerve
E. Deep peroneal nerve (Correct Answer)

Explanation: ***Deep peroneal nerve*** - The **deep peroneal nerve** (also known as the deep fibular nerve) innervates the muscles responsible for **dorsiflexion** of the foot (tibialis anterior, extensor digitorum longus, extensor hallucis longus, and fibularis tertius). Damage to this nerve results in **foot drop** and the inability to dorsiflex the foot. - It also provides sensory innervation to the **first dorsal web space** (between the great toe and the second toe), which is consistent with the patient's decreased sensation in this area. The **steppage gait** is a compensatory mechanism to avoid dragging the foot. *Superficial peroneal nerve* - The **superficial peroneal nerve** (superficial fibular nerve) primarily innervates the **peroneal muscles** (fibularis longus and brevis) responsible for **eversion** of the foot. - Sensory innervation is provided to the **dorsum of the foot**, except for the first dorsal web space and the lateral aspect of the heel. Damage would cause difficulty with eversion, not foot drop. *Saphenous nerve* - The **saphenous nerve** is a pure sensory nerve that supplies sensation to the **medial side of the leg** and foot. - It does not innervate any muscles, so it would not be implicated in a foot drop or motor deficit. *Sural nerve* - The **sural nerve** is a pure sensory nerve that provides sensation to the **posterolateral aspect of the leg**, the **lateral malleolus**, and the **lateral side of the foot** and little toe. - Like the saphenous nerve, it has no motor function and would not cause foot drop. *Tibial nerve* - The **tibial nerve** innervates the muscles of the **posterior compartment of the leg** and the intrinsic muscles of the foot. These muscles are responsible for **plantarflexion** and **inversion** of the foot. - Damage to the tibial nerve would result in difficulty with plantarflexion and toe flexion, leading to a calcaneal gait, not foot drop.

Question 12: A 21-year-old woman is brought to the emergency department following a motor vehicle collision. She has significant pain and weakness in her right arm and hand. Physical examination shows multiple ecchymoses and tenderness in the right upper extremity. She is able to make a fist, but there is marked decrease in grip strength. An x-ray of the right upper extremity shows a midshaft humerus fracture. Which of the following structures is most likely injured?

A. Radial artery
B. Median nerve
C. Ulnar nerve
D. Radial nerve (Correct Answer)
E. Brachial artery

Explanation: ***Radial nerve*** - A **midshaft humerus fracture** is classically associated with injury to the **radial nerve** because of its close proximity to the humerus in the **spiral groove**. - Injury to the radial nerve causes weakness in **wrist extension** and **grip strength** (due to inability to properly position the wrist), which aligns with the patient's presentation. *Radial artery* - The radial artery is located in the forearm and is not typically injured in a **midshaft humerus fracture**. - Injury to this artery would primarily affect distal perfusion and would not directly cause weakness in grip strength without other neurological signs. *Median nerve* - The median nerve provides sensation to the first three and a half digits and innervates most of the **flexor muscles** in the forearm and some hand muscles, including the thenar eminence. - While it can be injured in humeral fractures, a midshaft fracture is less likely to affect it compared to the radial nerve, and median nerve injury would present with different motor deficits (e.g., **"hand of benediction"**). *Ulnar nerve* - The ulnar nerve runs posterior to the medial epicondyle and then along the ulnar side of the forearm and hand, innervating intrinsic hand muscles and sensation to the medial 1.5 digits. - It is more commonly injured in **distal humeral fractures** (e.g., supracondylar fractures) or at the elbow, and injury would result in deficits like **claw hand deformity**, which are not described. *Brachial artery* - The brachial artery runs along the medial aspect of the humerus but is commonly injured in **supracondylar fractures** of the distal humerus, not typically midshaft fractures. - Injury to the brachial artery would present with signs of **ischemia**, such as pallor, pulselessness, sensory loss, and severe pain, which are not the primary complaints here.

Question 13: A 35-year-old woman, gravida 2, para 1, at 40 weeks' gestation, presents to the hospital with contractions spaced 2 minutes apart. Her past medical history is significant for diabetes, which she has controlled with insulin during this pregnancy. Her pregnancy has otherwise been unremarkable. A baby boy is born via a spontaneous vaginal delivery. Physical examination shows he weighs 4.5 kg (9 lb), the pulse is 140/min, the respirations are 40/min, and he has good oxygen saturation on room air. His left arm is pronated and medially rotated. He is unable to move it away from his body. The infant’s right arm functions normally and he is able to move his wrists and all 10 digits. Which of the following nerve roots were most likely damaged during delivery?

A. C4 and C5
B. C7 and C8
C. C5 and C6 (Correct Answer)
D. C8 and T1
E. C6 and C7

Explanation: ***C5 and C6*** - The presentation of the infant's left arm being **pronated**, **medially rotated**, and unable to be moved away from the body is characteristic of **Erb-Duchenne palsy** (also called "waiter's tip" deformity). - This condition results from damage to the **upper trunk of the brachial plexus**, specifically involving the **C5 and C6 nerve roots**. - These roots innervate muscles responsible for **shoulder abduction** (deltoid, supraspinatus), **external rotation** (infraspinatus), and **elbow flexion/supination** (biceps brachii). - The preserved wrist and digit function confirms the injury is limited to the upper trunk, sparing C7-T1. *C4 and C5* - While C5 is involved in Erb's palsy, the **C4 root** primarily contributes to the **phrenic nerve** (diaphragm innervation) and provides sensation to the neck and shoulder region. - C4 does not significantly contribute to the brachial plexus motor function, so damage to C4 would not explain the shoulder and elbow deficits observed. *C7 and C8* - Damage to **C7 and C8** would primarily affect **wrist extension** (C7) and **finger flexion** (C8), not the shoulder abduction and elbow flexion deficits seen here. - This pattern would be inconsistent with Erb's palsy and more suggestive of middle-to-lower trunk injury. *C8 and T1* - Injury to **C8 and T1** nerve roots causes **Klumpke's palsy**, affecting the **intrinsic hand muscles** and wrist flexors, leading to a "claw hand" deformity. - The infant's preserved ability to move all wrists and digits rules out C8-T1 injury, as this would severely impair hand function and potentially cause **Horner's syndrome** (if T1 is involved). *C6 and C7* - While **C6** is involved in Erb's palsy, adding **C7** damage would extend the injury to affect **wrist extensors** (extensor carpi radialis) and **triceps** (elbow extension). - The clinical presentation described is most consistent with isolated upper trunk (C5-C6) injury, not extended involvement of C7.

Question 14: A 35-year-old man comes to the physician because of a 3-month history of intermittent right lateral hip pain that radiates to the thigh. Climbing stairs and lying on his right side aggravates the pain. Examination shows tenderness to palpation over the upper lateral part of the right thigh. There is no swelling. When the patient is asked to abduct the right leg against resistance, tenderness is noted. An x-ray of the pelvis shows no abnormalities. Which of the following structures is the most likely source of this patient's pain?

A. Femoral head
B. Greater trochanter (Correct Answer)
C. Iliotibial band
D. Acetabulum
E. Lateral femoral cutaneous nerve

Explanation: ***Greater trochanter*** - The patient's symptoms of **intermittent right lateral hip pain** radiating to the thigh, aggravated by climbing stairs and lying on the affected side, and tenderness over the **upper lateral part of the right thigh** are classic signs of **trochanteric bursitis**. - Pain with **resisted abduction** further points to inflammation of the **gluteus medius** or its associated bursa at the greater trochanter. *Femoral head* - Pain originating from the **femoral head** typically presents as deep, generalized groin or hip joint pain, often exacerbated by weight-bearing activities, and may be associated with limited range of motion in multiple planes. - An **x-ray showing no abnormalities** makes femoral head issues like avascular necrosis or significant arthritis less likely. *Iliotibial band* - **Iliotibial band (ITB) syndrome** usually causes pain along the **lateral aspect of the knee**, particularly in runners or cyclists, due to friction over the lateral femoral epicondyle. - While the ITB traverses the lateral thigh, the primary point of tenderness and mechanism of pain in this case (tenderness over the upper lateral thigh, pain with resisted abduction) is not typical for ITB syndrome affecting the knee. *Acetabulum* - Pain from the **acetabulum** would generally be deep within the hip joint, similar to femoral head issues, and often accompanied by a **limited range of motion** or clicking/locking sensations, and would be associated with intra-articular pathology. - An **unremarkable X-ray** and the specific finding of **tenderness over the lateral thigh** make acetabular pathology less likely. *Lateral femoral cutaneous nerve* - Entrapment of the **lateral femoral cutaneous nerve** (meralgia paresthetica) typically causes **numbness, burning, or tingling** on the anterolateral thigh, not primarily sharp, intermittent pain aggravated by movement and palpation in the manner described. - While pain can be present, the absence of **paresthesias** and the mechanical nature of the pain (aggravated by resisted abduction) make nerve entrapment less probable.

Question 15: A healthy 28-year-old woman at 30-weeks gestational age, has gained 35lbs since becoming pregnant. She complains of several weeks of bilateral numbness and tingling of her palms, thumbs, index and middle fingers that is worse at night. She also notes weakness gripping objects at the office. Which nerve is most likely affected?

A. Anterior interosseous nerve
B. Median nerve (Correct Answer)
C. Axillary nerve
D. Radial nerve
E. Ulnar nerve

Explanation: ***Median nerve*** - The symptoms of **numbness and tingling in the palms, thumb, index, and middle fingers**, especially worsening at night, are classic for **carpal tunnel syndrome**. The **median nerve** is compressed within the carpal tunnel. - The patient's pregnancy and weight gain are **risk factors** for carpal tunnel syndrome due to fluid retention and swelling, which can increase pressure on the median nerve. *Anterior interosseous nerve* - This nerve is a purely **motor branch of the median nerve** and its compression would primarily cause weakness in specific forearm muscles, affecting the **pincer grasp** (flexion of the thumb and index finger). - It does not typically cause **sensory symptoms** in the palm or fingers, which are prominent in this patient's presentation. *Axillary nerve* - The **axillary nerve** innervates the **deltoid muscle** and provides sensation over the lateral shoulder. - Injury would result in **shoulder weakness** (especially abduction) and sensory loss over the lateral arm, not hand or finger symptoms. *Radial nerve* - Compression or injury to the **radial nerve** typically causes **wrist drop** (inability to extend the wrist and fingers) and sensory loss over the posterior forearm and dorsal hand. - It does not innervate the palm, thumb, or index finger in the distribution described by the patient. *Ulnar nerve* - The **ulnar nerve** innervates the **little finger and half of the ring finger**, as well as intrinsic hand muscles. - Compression would cause numbness and tingling in that distribution, along with weakness in handgrip, but not in the thumb, index, and middle fingers.

Question 16: A 43-year-old man comes to the physician because of a swelling at the back of his left knee that he first noticed 2 months ago. The swelling is not painful, but he occasionally experiences pain at the back of his knee when he is standing for prolonged periods. He also reports mild stiffness of the knee when he wakes up in the morning that disappears after a few minutes of waking up and moving about. Examination shows no local calf tenderness, but forced dorsiflexion of the foot aggravates his knee pain. There is a 3-cm, mildly tender, fixed mass at the medial side of the left popliteal fossa. The mass is more prominent on extension and disappears upon flexion of the left knee. Which of the following is the strongest predisposing risk factor for this patient's condition?

A. Family history of multiple lipomatosis
B. History of meniscal tear (Correct Answer)
C. Purine-rich diet
D. Mutation of coagulation factor V gene
E. Varicose veins

Explanation: ***History of meniscal tear*** - The patient's presentation with a **non-painful popliteal swelling**, morning stiffness, and pain with prolonged standing is highly suggestive of a **Baker's cyst**. - A Baker's cyst, also known as a popliteal cyst, is typically a secondary condition arising from underlying knee joint pathology, with a **meniscal tear** being a very common predisposing factor due to increased intra-articular pressure and fluid accumulation. *Family history of multiple lipomatosis* - **Lipomatosis** involves the presence of multiple benign fatty tumors (**lipomas**) and is not directly related to the formation of a Baker's cyst, which is a fluid-filled sac. - While lipomas can occur, they do not cause the specific symptoms of knee stiffness, pain with prolonged standing, or the characteristic changes in prominence with knee flexion/extension seen in this case. *Purine-rich diet* - A **purine-rich diet** is a risk factor for **gout**, a form of inflammatory arthritis caused by uric acid crystal deposition. - Gout typically presents with acute, painful joint inflammation and swelling, which is distinct from the described painless popliteal swelling and mild stiffness. *Mutation of coagulation factor V gene* - A mutation in the **coagulation factor V gene** (e.g., Factor V Leiden) increases the risk of **thrombosis** and **deep vein thrombosis (DVT)**. - While a DVT can cause calf swelling and pain, the mass described is fixed, more prominent on extension, and disappears on flexion, which is characteristic of a Baker's cyst, not a DVT. *Varicose veins* - **Varicose veins** are dilated and tortuous superficial veins, often found in the lower extremities, and are associated with chronic venous insufficiency. - Varicose veins do not cause the formation of a popliteal cyst or the specific knee mechanical symptoms described; they present as visible dilated veins and leg discomfort, sometimes swelling, but not a distinct fixed mass in the popliteal fossa that changes with knee position.

Question 17: Eighteen hours after the vaginal delivery of a 2788-g (6-lb 2-oz) newborn, a 22-year-old woman has weakness and numbness of her right foot. She is unable to walk without dragging and shuffling the foot. The delivery was complicated by prolonged labor and had received epidural analgesia. There is no personal or family history of serious illness. Her temperature is 37.3°C (99.1°F), pulse is 98/min, and blood pressure is 118/70 mm Hg. Examination shows a high-stepping gait. There is weakness of right foot dorsiflexion and right ankle eversion. Sensation is decreased over the dorsum of the right foot and the anterolateral aspect of the right lower extremity below the knee. Deep tendon reflexes are 2+ bilaterally. The remainder of the examination shows no abnormalities. Which of the following is the most likely cause of this patient's symptoms?

A. Postpartum angiopathy
B. Lateral femoral cutaneous nerve injury
C. Compression of the common peroneal nerve (Correct Answer)
D. Effect of epidural anesthesia
E. L2-L4 radiculopathy

Explanation: ***Compression of the common peroneal nerve*** - The patient's symptoms, including **right foot dorsiflexion weakness** (**foot drop**), **ankle eversion weakness**, decreased sensation over the **dorsum of the right foot** and **anterolateral aspect of the right lower leg**, and a **high-stepping gait**, are classic signs of common peroneal nerve injury. - **Prolonged labor** in the **dorsal lithotomy position** can lead to compression of the common peroneal nerve as it wraps around the **head of the fibula**, causing temporary or permanent damage. *Postpartum angiopathy* - This condition involves **vascular inflammation** or occlusion, which would typically present with more diffuse or severe neurological deficits, potentially involving multiple limbs or cranial nerves. - It is not specifically associated with isolated common peroneal nerve symptoms. *Lateral femoral cutaneous nerve injury* - Injury to the lateral femoral cutaneous nerve (**meralgia paresthetica**) causes numbness and pain specifically over the **lateral thigh**. - It does not cause **foot drop**, ankle eversion weakness, or sensory deficits in the foot or anterolateral leg. *Effect of epidural anesthesia* - While epidural anesthesia can cause transient leg weakness or numbness, these effects are usually **bilateral** and resolve within a few hours of discontinuing the anesthesia. - The patient's symptoms are **unilateral** and persistent 18 hours postpartum, making direct epidural effect less likely as the primary cause. *L2-L4 radiculopathy* - **L2-L4 radiculopathy** would primarily affect hip flexion, knee extension, and sensation over the anterior thigh, potentially causing quadriceps weakness and loss of the patellar reflex. - It would not typically result in isolated **foot drop**, ankle eversion weakness, or the specific sensory distribution associated with common peroneal nerve injury.

Question 18: A 42-year-old woman comes to the physician because of increasing pain in the right hip for 2 months. The pain is intermittent, presenting at the lateral side of the hip and radiating towards the thigh. It is aggravated while climbing stairs or lying on the right side. Two weeks ago, the patient was treated with a course of oral prednisone for exacerbation of asthma. Her current medications include formoterol-budesonide and albuterol inhalers. Vital signs are within normal limits. Examination shows tenderness to palpation over the upper lateral part of the right thigh. There is no swelling. The patient is placed in the left lateral decubitus position. Abducting the extended right leg against the physician's resistance reproduces the pain. The remainder of the examination shows no abnormalities. An x-ray of the pelvis shows no abnormalities. Which of the following is the most likely diagnosis?

A. Osteoarthritis of the hip
B. Osteonecrosis of femoral head
C. Lumbosacral radiculopathy
D. Greater trochanteric pain syndrome (Correct Answer)
E. Iliotibial band syndrome

Explanation: ***Greater trochanteric pain syndrome*** - The patient's symptoms of **lateral hip pain** radiating to the thigh, aggravated by activity and lying on the affected side, and **tenderness over the greater trochanter** are classic for **greater trochanteric pain syndrome** (GTPS). - Pain reproduction with **abduction against resistance** (a specific test for GTPS) and normal X-rays further support this diagnosis. *Osteoarthritis of the hip* - Typically causes **groin pain** that can radiate to the buttock or knee, not primarily lateral hip pain. - X-rays would likely show signs of **joint space narrowing**, osteophytes, or subchondral sclerosis, which are absent here. *Osteonecrosis of femoral head* - While **corticosteroid use** is a risk factor, osteonecrosis usually presents with **groin or buttock pain** and would likely show abnormalities on X-ray (advanced stages) or MRI (early stages). - The specific tenderness and pain reproduction with abduction against resistance are not typical for osteonecrosis. *Lumbosacral radiculopathy* - Would typically present with pain radiating **down the leg** in a dermatomal pattern, often accompanied by **neurological deficits** such as sensory loss, weakness, or reflex changes. - The examination findings of isolated lateral hip tenderness and pain with resisted abduction do not support radiculopathy. *Iliotibial band syndrome* - More commonly affects **runners** or cyclists and causes pain along the **lateral aspect of the knee**, although it can present as lateral hip pain. - While it can manifest with lateral hip pain, the focal tenderness over the greater trochanter and pain on resisted abduction make **GTPS** a more precise diagnosis.

Question 19: A 38-year-old man is brought to the emergency department after suffering a motor vehicle accident as the passenger. He had no obvious injuries, but he complains of excruciating right hip pain. His right leg is externally rotated, abducted, and extended at the hip and the femoral head can be palpated anterior to the pelvis. Plain radiographs of the pelvis reveal a right anterior hip dislocation and femoral head fracture. Which sensory and motor deficits are most likely in this patient's right lower extremity?

A. Loss of sensation laterally below the knee, weak thigh extension and knee flexion
B. Numbness of the ipsilateral scrotum and upper medial thigh
C. Sensory loss to the dorsal surface of the foot and part of the anterior lower and lateral leg and foot drop
D. Paresis and numbness of the medial thigh and medial side of the calf, weak hip flexion and knee extension
E. Numbness of the medial side of the thigh and inability to adduct the thigh (Correct Answer)

Explanation: ***Numbness of the medial side of the thigh and inability to adduct the thigh*** - An **anterior hip dislocation** is caused by forced **abduction** and **external rotation**, putting the **obturator nerve** at risk due to its anatomical course through the **obturator foramen** and proximity to the hip joint. - Damage to the **obturator nerve** (L2-L4) results in **sensory loss** over the **medial thigh** and paralysis of the **adductor muscles** (adductor longus, brevis, magnus, gracilis), leading to an inability to adduct the thigh. *Loss of sensation laterally below the knee, weak thigh extension and knee flexion* - **Sensory loss laterally below the knee** and **weak thigh extension/knee flexion** are characteristic of **sciatic nerve** or common **peroneal nerve injury**, which is more common in **posterior hip dislocations**. - The presented case describes an **anterior dislocation**, making **obturator nerve** injury more likely than sciatic nerve injury. *Numbness of the ipsilateral scrotum and upper medial thigh* - **Numbness of the ipsilateral scrotum** and **upper medial thigh** is associated with injury to the **ilioinguinal nerve** or **genitofemoral nerve**. - While these nerves supply portions of the **medial thigh** and **genitalia**, they are not typically injured in **anterior hip dislocations** which primarily affect deeper structures like the **obturator nerve**. *Sensory loss to the dorsal surface of the foot and part of the anterior lower and lateral leg and foot drop* - **Sensory loss to the dorsal surface of the foot**, **anterior lower and lateral leg**, and **foot drop** are classic signs of **common peroneal nerve** injury due to its superficial course around the fibular head. - Although the common peroneal nerve is a branch of the **sciatic nerve**, direct injury specifically to the **common peroneal nerve** in an anterior hip dislocation is less probable than obturator nerve injury, and foot drop is characteristic of more severe neural compromise, typically seen in **posterior dislocations or direct trauma**. *Paresis and numbness of the medial thigh and medial side of the calf, weak hip flexion and knee extension* - **Paresis and numbness of the medial thigh** are consistent with **obturator nerve** injury. However, **numbness of the medial side of the calf** and **weak hip flexion/knee extension** point towards **femoral nerve** injury. - While the **femoral nerve** can be injured, the prominent clinical picture of **anterior hip dislocation** points more directly to the **obturator nerve** findings of medial thigh numbness and adduction weakness, rather than primarily femoral nerve symptoms.

Question 20: A 19-year-old man comes to the emergency department for right wrist pain and swelling 2 hours after falling on an outstretched hand while playing softball. The pain worsened when he attempted to pitch after the fall. He has eczema and type 1 diabetes mellitus. Current medications include insulin and topical clobetasol. He appears uncomfortable. Examination shows multiple lichenified lesions over his forearms. The right wrist is swollen and tender; range of motion is limited by pain. There is tenderness to palpation in the area between the tendons of the abductor pollicis longus, extensor pollicis brevis, and extensor pollicis longus muscle. The thumb can be opposed actively towards the other fingers. Muscle strength of the right hand is decreased. Which of the following is the most likely diagnosis?

A. De Quervain's tenosynovitis
B. Colles' fracture
C. Transscaphoid perilunate dislocation
D. Scaphoid fracture (Correct Answer)
E. Lunate dislocation

Explanation: ***Scaphoid fracture*** - The history of a **fall on an outstretched hand (FOOSH)**, especially when attempting to pitch again, combined with **tenderness in the anatomical snuffbox** (area between the tendons of the abductor pollicis longus, extensor pollicis brevis, and extensor pollicis longus muscle), is highly indicative of a **scaphoid fracture**. - **Limited range of motion** and decreased muscle strength due to pain, even with active thumb opposition, further supports this diagnosis. *De Quervain's tenosynovitis* - This is an **inflammatory condition** affecting the tendons on the thumb side of the wrist, typically exacerbated by repetitive thumb movements. - While it can cause pain in a similar area, it usually develops gradually and is not immediately precipitated by an acute **FOOSH injury**. *Colles' fracture* - A **Colles' fracture** involves a fracture of the **distal radius** with dorsal displacement, often presenting with a "dinner fork" deformity. - While it also results from a **FOOSH injury**, the key finding of **anatomical snuffbox tenderness** points away from a Colles' fracture and towards a scaphoid injury. *Transscaphoid perilunate dislocation* - This severe injury involves a **dislocation of the carpal bones** around the lunate, often with an associated scaphoid fracture. - While a scaphoid fracture is part of this, the primary presentation would involve more obvious **carpal instability** and significant radiographic abnormalities beyond a simple scaphoid fracture. *Lunate dislocation* - A **lunate dislocation** involves the displacement of the lunate bone, typically volarly, and often presents with a characteristic "spilled teacup" sign on radiographs. - Although it can result from a **FOOSH injury**, the specific finding of **anatomical snuffbox tenderness** is more indicative of a scaphoid fracture.

Question 21: A 64-year-old man with osteoarthritis of the knee comes to the physician for evaluation of weakness in his foot. Physical examination shows a swelling in the popliteal fossa. There is weakness when attempting to plantarflex and invert his right foot. He is unable to curl his toes. Further evaluation of this patient is most likely to show decreased sensation over which of the following locations?

A. First dorsal web space
B. Sole of the foot (Correct Answer)
C. Lateral border of the foot
D. Medial plantar arch
E. Second dorsal web space

Explanation: ***Sole of the foot*** - The patient's inability to **plantarflex the foot**, weakness with **inversion**, and inability to **curl the toes** indicate damage to the **tibial nerve**. - A **popliteal fossa mass** (likely Baker's cyst) can compress the tibial nerve as it courses through this region. - The **tibial nerve** supplies sensation to the **sole of the foot** via its medial and lateral plantar branches and innervates the muscles responsible for plantarflexion, foot inversion (tibialis posterior), and toe flexion. *First dorsal web space* - Sensation over the **first dorsal web space** is primarily supplied by the **deep fibular (peroneal) nerve**. - Injury to this nerve would typically affect **dorsiflexion** and **toe extension**, not the plantarflexion and toe flexion deficits described. *Lateral border of the foot* - Sensation along the **lateral border of the foot** is predominantly supplied by the **sural nerve**. - This nerve is primarily cutaneous and does not contribute to motor function related to plantarflexion or toe curling. *Medial plantar arch* - While the **medial plantar nerve** (a branch of the tibial nerve) supplies sensation to part of the plantar surface, the term "sole of the foot" more comprehensively describes the entire plantar sensory distribution of the tibial nerve. - The motor deficits described indicate a proximal **tibial nerve** lesion affecting the entire nerve distribution. *Second dorsal web space* - Sensation to the **second dorsal web space** is primarily provided by the **superficial fibular (peroneal) nerve**. - Motor deficits associated with fibular nerve injury would be dorsiflexion and eversion weakness, not the symptoms described.

Question 22: A 39-year-old male who recently presented with acetaminophen overdose was admitted to the MICU, where several attempts were made at obtaining intravenous access without success. The decision was made to place a right axillary arterial line, which became infected and was removed by the medical student while the patient was still intubated. It was later noticed that he had substantial swelling and bruising of the upper extremity. Given his sedation, a proper neuro exam was not performed at that time. Several days later, after the patient's liver function improved, he was successfully extubated. On exam, he complained of lack of sensation over the palmar and dorsal surface of the small finger and half of the ring finger, as well as weak digit abduction, weak thumb adduction, and weak thumb-index finger pinch of the affected extremity. What is the most likely cause and corresponding location of the injury?

A. Compression of ulnar nerve secondary to coagulopathy (Correct Answer)
B. Compression of median nerve secondary to coagulopathy
C. Stretch injury to ulnar nerve secondary to frequent repositioning
D. Needle injury to ulnar nerve secondary to blind line placement
E. Needle injury to median nerve secondary to blind line placement

Explanation: ***Compression of ulnar nerve secondary to coagulopathy*** - The described sensory deficits (palmar and dorsal surface of the small finger and half of the ring finger) and motor deficits (weak digit abduction, weak thumb adduction, and weak thumb-index finger pinch) are classic signs of **ulnar nerve injury**. - The patient's history of an infected axillary arterial line, substantial upper extremity swelling/bruising, and likely **coagulopathy** (given acetaminophen overdose and liver dysfunction) predispose to hemorrhage and compression of the ulnar nerve in the axillary region or more distally. *Compression of median nerve secondary to coagulopathy* - **Median nerve injury** would typically present with sensory loss over the thumb, index, middle finger, and radial half of the ring finger, as well as weakness in thumb abduction and opposition. These findings are inconsistent with the patient's symptoms. - While coagulopathy could cause nerve compression, the specific neurological deficits point away from the median nerve. *Stretch injury to ulnar nerve secondary to frequent repositioning* - While repositioning can cause stretch injuries, the context of an infected arterial line insertion, swelling, and bruising strongly suggests a **compressive etiology** rather than just a stretch injury. - The degree of injury and the associated swelling make compression a more probable cause than simple stretch. *Needle injury to ulnar nerve secondary to blind line placement* - While blind line placement can cause needle injury, the delayed onset of symptoms after line removal, combined with the presence of **substantial swelling and bruising**, suggests a developing hematoma or compressive process rather than direct acute needle trauma. - Direct needle injury would typically manifest immediately or very soon after the attempted placement. *Needle injury to median nerve secondary to blind line placement* - As with other median nerve options, the sensory and motor symptoms provided in the clinical vignette do not align with a **median nerve injury**. - Furthermore, the clinical picture points to a compressive injury developing over time due to bleeding rather than a direct needle strike onto a nerve, especially given the axillary location where the median nerve is well protected within the neurovascular bundle.

Question 23: A 47-year-old woman presents to her primary care provider because of numbness and tingling on the palmar aspects of both hands. She denies any symptoms at the base of her thumbs. The symptoms are worse on the right (dominant hand) and are increased with activities such as driving or brushing her hair. She frequently wakes up with pain and has to shake her hand for pain relief. She has had rheumatoid arthritis for 9 years, for which she takes methotrexate. Her blood pressure is 124/76 mm Hg, the heart rate is 75/min, and the respiratory rate is 15/min. Lightly tapping over the middle of the anterior aspect of the right wrist leads to a tingling sensation in the palm. In this patient, electromyography (EMG) will most likely show which of the following results?

A. Neuropathic changes in the palmar branch of the median nerve
B. Denervation in C7 innervated paraspinal, arms, and shoulder muscles
C. Focal slowing of conduction velocity in the median nerve in the carpal tunnel (Correct Answer)
D. Widespread symmetrical neuropathic changes without focal abnormalities
E. Widespread denervation in proximal muscles with normal sensory nerves

Explanation: ***Focal slowing of conduction velocity in the median nerve in the carpal tunnel*** - The patient's symptoms (numbness, tingling in palmar hands, worsening with activity, nocturnal pain relieved by shaking, **Tinel's sign** at the wrist) are classic for **carpal tunnel syndrome (CTS)**, caused by compression of the **median nerve** at the wrist. - **Electromyography (EMG)** and **nerve conduction studies (NCS)** are confirmatory tests for CTS, demonstrating slowed conduction velocity specifically through the carpal tunnel. *Neuropathic changes in the palmar branch of the median nerve* - The **palmar cutaneous branch** of the median nerve typically branches off **proximal to the carpal tunnel** and supplies sensation to the base of the thumb. - Since the patient specifically denies symptoms at the base of her thumbs, isolated involvement of the palmar cutaneous branch is unlikely in this case, pointing to compression within the carpal tunnel. *Denervation in C7 innervated paraspinal, arms, and shoulder muscles* - **C7 radiculopathy** would involve symptoms in the C7 dermatome and myotome, potentially affecting muscles in the arm and shoulder. - Her symptoms are primarily wrist and hand-focused, without signs of cervical spine involvement or widespread muscle weakness. *Widespread symmetrical neuropathic changes without focal abnormalities* - This pattern suggests a **generalized peripheral neuropathy**, which would likely present with more diffuse and possibly symmetrical symptoms, often involving the feet first. - This patient's symptoms are distinctly focal and related to the distribution of the median nerve in the hand. *Widespread denervation in proximal muscles with normal sensory nerves* - This presentation is more consistent with a **motor neuron disease** or a **myopathy**, where there is primarily motor involvement and sensory nerves are typically spared. - The patient's primary symptoms are sensory (numbness and tingling), and there is no indication of widespread muscle weakness or atrophy typical of denervation in proximal muscles.

Question 24: Three hours after undergoing left hip arthroplasty for chronic hip pain, a 62-year-old man complains of a prickling sensation in his left anteromedial thigh and lower leg. He has never had these symptoms before. He has hyperlipidemia and coronary artery disease. He has had recent right-sided gluteal and thigh pain with ambulation. Vital signs are within normal limits. Sensation to pinprick and light touch are decreased on the anteromedial left thigh as well as medial lower leg. Neurologic exam shows left leg strength 3/5 on hip flexion and 2/5 on knee extension. Patellar reflex is decreased on the left. The remainder of neurologic exam is normal. Dorsalis pedis, popliteal, and femoral pulses are 2+ bilaterally. The surgical incision is without erythema or drainage. Which of the following is the most likely underlying cause of this patient's symptoms?

A. Surgical site infection
B. Obturator nerve injury
C. Sural nerve injury
D. Femoral nerve injury (Correct Answer)
E. Femoral artery occlusion

Explanation: ***Femoral nerve injury*** - The patient's symptoms of **prickling sensation (paresthesia)** in the anterior-medial thigh and medial lower leg, **decreased sensation to pinprick and light touch** in these areas, and **weakness in hip flexion (iliopsoas)** and **knee extension (quadriceps)**, along with a **decreased patellar reflex**, are all classic signs of **femoral nerve dysfunction**. - The femoral nerve can be susceptible to injury during **hip arthroplasty** due to retraction, direct trauma, or hematoma formation, especially if the patient is slim or has anatomical variations. *Surgical site infection* - This typically presents with signs of **inflammation** such as erythema, warmth, severe pain, and sometimes drainage from the incision site, which are absent here. - Neurological deficits like specific motor weakness and sensory loss in a nerve distribution are *not* primary features of a surgical site infection. *Obturator nerve injury* - An obturator nerve injury would primarily affect **adduction of the thigh** and might cause sensory changes in the medial thigh, but would *not* cause weakness in hip flexion or knee extension, nor would it affect the patellar reflex. - The sensory distribution described (anteromedial thigh and medial lower leg) is more consistent with femoral nerve involvement than obturator nerve. *Sural nerve injury* - **Sural nerve injury** primarily causes sensory deficits along the **posterolateral aspect of the lower leg and ankle**, and the lateral aspect of the foot. - It would *not* cause motor weakness in hip flexion or knee extension, nor would it affect the patellar reflex. *Femoral artery occlusion* - **Femoral artery occlusion** would cause symptoms of **acute limb ischemia**, including severe pain, pallor, pulselessness, poikilothermia (coldness), paresthesias, and paralysis (the "6 Ps"). - While paresthesias are present, the patient has **intact distal pulses (2+ bilaterally)** and no signs of pallor or coldness, ruling out significant arterial occlusion.

Question 25: A 48-year-old male presents to his primary care provider with a two-week history of low back pain and left leg pain. He reports that his symptoms started while he was working at his job as a construction worker. He has since experienced intermittent achy pain over his lumbar spine. He has also noticed pain radiating into his left leg and weakness in left ankle dorsiflexion. On exam, he demonstrates the following findings on strength testing of the left leg: 5/5 in knee extension, 4/5 in ankle dorsiflexion, 4/5 in great toe extension, 5/5 in ankle plantarflexion, and 5/5 in great toe flexion. The patellar reflexes are 5/5 bilaterally. He is able to toe walk but has difficulty with heel walking. Weakness in which of the following compartments of the leg is most likely causing this patient’s foot drop?

A. Lateral compartment
B. Superficial posterior compartment
C. Deep posterior compartment
D. Anterior compartment (Correct Answer)
E. Medial compartment

Explanation: ***Anterior compartment*** - Weakness in **ankle dorsiflexion** and **great toe extension**, coupled with difficulty **heel walking**, indicates a foot drop due to dysfunction of muscles in the anterior compartment, such as the **tibialis anterior**, **extensor hallucis longus**, and **extensor digitorum longus**. - These muscles are primarily innervated by the **deep fibular nerve**, which is susceptible to compression from conditions like **lumbar radiculopathy** (L4-L5 nerve root involvement). *Lateral compartment* - Muscles in the lateral compartment (**fibularis longus** and **brevis**) are responsible for **eversion** of the foot. - Weakness in this compartment would manifest as difficulty everting the foot, not primarily ankle dorsiflexion or great toe extension deficits. *Superficial posterior compartment* - This compartment contains muscles like the **gastrocnemius** and **soleus**, which are primarily responsible for **ankle plantarflexion**. - The patient exhibits 5/5 strength in ankle plantarflexion and is able to toe walk, indicating these muscles are functioning well. *Deep posterior compartment* - Muscles in the deep posterior compartment (**tibialis posterior**, **flexor digitorum longus**, **flexor hallucis longus**) are involved in **inversion** and **toe flexion**. - The patient has 5/5 strength in great toe flexion, suggesting intact function of these muscles, and his primary deficit is in dorsiflexion. *Medial compartment* - There is no distinct "medial compartment" of the leg in the anatomical sense comparable to the other listed compartments; rather, various muscles contribute to medial actions. - The symptoms described specifically point to weakness in dorsiflexion and toe extension, localizing the problem to the anterior compartment.

Question 26: A 2-day-old boy is evaluated in the nursery for minimal movement in his left upper limb. He was born at 41 weeks gestation by an assisted forceps-vaginal delivery to a 42-year-old obese woman. Birth weight was 4.4 kg (9.7 lb). The mother had 4 previous vaginal deliveries, all requiring forceps. Examinations of the left upper limb show that the arm hangs by his side and is rotated medially. His forearm is extended and pronated, and his wrist and fingers are flexed. Moro reflex is present only on the right side. Which of the following muscles was spared from the injury sustained during delivery?

A. Biceps
B. Supraspinatus
C. Infraspinatus
D. Deltoid
E. Triceps (Correct Answer)

Explanation: ***Triceps*** - The patient's presentation is consistent with **Erb-Duchenne palsy**, affecting the **C5-C6 nerve roots** of the brachial plexus. - The **triceps muscle** is innervated by the **radial nerve** originating from **C6, C7, and C8**, with **C7 and C8 providing the predominant innervation**. - Since the injury involves primarily **C5-C6**, and the triceps depends mainly on **C7-C8**, it is **functionally spared** in Erb's palsy. *Biceps* - The **biceps muscle** is innervated by the **musculocutaneous nerve** (C5-C6) and is responsible for **flexion and supination** of the forearm. - Its involvement explains the **extended and pronated** forearm observed in Erb's palsy. *Supraspinatus* - The **supraspinatus muscle** is innervated by the **suprascapular nerve** (C5-C6) and is crucial for the **initiation of shoulder abduction**. - Injury to its innervation contributes to the arm hanging by the side. *Infraspinatus* - The **infraspinatus muscle** is also innervated by the **suprascapular nerve** (C5-C6) and is responsible for **external rotation** of the humerus. - Its paralysis leads to the **medially rotated** arm seen in Erb's palsy. *Deltoid* - The **deltoid muscle** is innervated by the **axillary nerve** (C5-C6) and primarily functions in **shoulder abduction** and shoulder flexion/extension. - Damage to this innervation contributes to the inability to abduct the arm.

Question 27: A 12-year-old boy is brought to his orthopedic surgeon for evaluation of leg pain and positioning. Specifically, over the past several months he has been complaining of thigh pain and has more difficulty sitting in his wheelchair. His medical history is significant for spastic quadriplegic cerebral palsy since birth and has undergone a number of surgeries for contractures in his extremities. At this visit his legs are found to be scissored such that they cross each other at the knees and are difficult to separate. Surgery is performed and the boy is placed into a cast that keeps his legs abducted to prevent scissoring. Overactivity of the muscles innervated by which of the following nerves is most consistent with this patient's deformity?

A. Nerve to the iliopsoas
B. Sciatic nerve
C. Femoral nerve
D. Superior gluteal nerve
E. Obturator nerve (Correct Answer)

Explanation: ***Obturator*** - The **obturator nerve** innervates the **adductor muscles** of the thigh (adductor longus, brevis, magnus, gracilis, and obturator externus). - **Overactivity** of these muscles leads to thigh adduction, causing the characteristic **"scissoring" gait** seen in some patients with cerebral palsy. *Nerve to the iliopsoas* - The **iliopsoas muscle** is a primary **hip flexor**, important for activities like sitting and standing. - While involvement of hip flexors can cause contractures, it would manifest as difficulty extending the hip, not a scissoring deformity. *Sciatic nerve* - The **sciatic nerve** innervates the **hamstring muscles** (semitendinosus, semimembranosus, biceps femoris) and most muscles of the leg and foot. - Its overactivity or spasticity would primarily affect knee flexion and foot movements, not hip adduction or scissoring. *Femoral nerve* - The **femoral nerve** innervates the **quadriceps femoris muscles** (rectus femoris, vastus lateralis, medialis, intermedius) and the sartorius. - Overactivity would lead to strong knee extension and hip flexion, not the adducted and scissored leg position described. *Superior gluteal nerve* - The **superior gluteal nerve** innervates the **gluteus medius**, **gluteus minimus**, and **tensor fasciae latae** muscles, which are primarily hip abductors and internal rotators. - Overactivity of these muscles would cause hip abduction, which is the opposite of the scissoring deformity.

Question 28: A 25-year-old man was referred to a neurologist for right-hand weakness. He was involved in a motor vehicle accident 2 months ago in which his right hand was injured. On examination, his grip is weak, especially in fingers 2, 4, and 5 and he is unable to adduct these fingers. Which of the following groups of muscles is most likely affected?

A. Flexor digitorum profundus
B. Palmar interossei muscles (Correct Answer)
C. Lumbrical muscles
D. Dorsal interossei muscles
E. Extensor digitorum

Explanation: ***Palmar interossei muscles*** - The inability to **adduct fingers 2, 4, and 5** (index, ring, and pinky fingers) is the key finding. The **palmar interossei** are responsible for adduction of these fingers towards the middle finger. - Weak grip in these specific fingers indicates impairment of the muscles controlling their movement and adduction, which are primarily the palmar interossei. *Flexor digitorum profundus* - The **flexor digitorum profundus** primarily **flexes the distal interphalangeal (DIP) joints** of the fingers, as well as assists in flexing the proximal interphalangeal (PIP) and metacarpophalangeal (MCP) joints. - While it contributes to grip strength, its primary role is flexion, not adduction, and weakness would typically present as difficulty with deep finger flexion rather than specific adduction issues. *Lumbrical muscles* - The **lumbrical muscles** **flex the metacarpophalangeal (MCP) joints** and **extend the interphalangeal (IP) joints**. This action is characteristic of the "lumbrical grip" or "writing position." - Their primary function does not involve adduction of the fingers, and their weakness would manifest differently. *Dorsal interossei muscles* - The **dorsal interossei muscles** are responsible for **abduction of the fingers** (spreading them apart). - The patient's inability to adduct fingers rules out the dorsal interossei as the primary affected group, as these muscles perform the opposite action. *Extensor digitorum* - The **extensor digitorum** primarily **extends the metacarpophalangeal (MCP) and interphalangeal (IP) joints** of the medial four fingers. - Weakness in this muscle would result in difficulty extending the fingers, leading to a "dropped finger" appearance or inability to straighten the fingers, which is contrary to the described adduction deficit.

Question 29: A 25-year-old woman comes to the physician because of pain and weakness in her right forearm and hand for several months. Two years ago, she sustained a fracture of her ulnar shaft with dislocation of the radial head that was treated surgically. Physical examination shows mild tenderness a few centimeters distal to the lateral epicondyle. She has marked weakness when attempting to extend her right middle finger. There is radial deviation on extension of the wrist. Sensation is not impaired. Which of the following nerves is most likely affected in this patient?

A. Ulnar nerve
B. Musculocutaneous nerve
C. Posterior interosseous nerve (Correct Answer)
D. Superficial radial nerve
E. Anterior interosseous nerve

Explanation: ***Posterior interosseous nerve*** - The symptoms, including weakness in **middle finger extension** and **radial deviation of the wrist on extension**, are classic signs of **posterior interosseous nerve** (PIN) palsy. This nerve primarily innervates the muscles responsible for **finger and thumb extension**, as well as **extensor carpi ulnaris** (ECU) for wrist extension. - The **radial deviation on wrist extension** occurs because the radial-sided wrist extensors (**extensor carpi radialis longus** and **brevis**) are innervated by the **radial nerve proper** before it branches into PIN, so they remain intact. With loss of ECU (ulnar-sided wrist extensor), unopposed action of ECRL and ECRB causes radial deviation. - PIN palsy can result from **trauma** or compression, and the patient's history of a **radial head dislocation** two years prior is a significant risk factor for nerve damage in this region, particularly as PIN passes through the **supinator muscle** (arcade of Frohse). Tenderness distal to the **lateral epicondyle** also points to the region where PIN can be compressed. *Ulnar nerve* - An **ulnar nerve** injury would primarily cause weakness in **finger adduction and abduction** (especially the little finger and ring finger), **flexion of the ulnar half of the profundus**, and **intrinsic hand muscles**, leading to a "claw hand" deformity if severe. - Sensation would also be affected in the **palmar and dorsal aspects of the 5th digit** and the **medial half of the 4th digit**, which is not described. *Musculocutaneous nerve* - The **musculocutaneous nerve** primarily innervates the **biceps brachii** and **brachialis muscles**, responsible for **elbow flexion** and **forearm supination**. - Sensory deficits would be noted on the **lateral forearm**, none of which align with the patient's symptoms. *Superficial radial nerve* - The **superficial radial nerve** is purely sensory and provides sensation to the **dorsum of the hand** and parts of the thumb, index, and middle fingers. - It does not have any motor function, so motor weakness would not be a symptom of its injury. *Anterior interosseous nerve* - The **anterior interosseous nerve** (AIN) is a purely motor branch of the median nerve, responsible for innervating the **flexor pollicis longus**, **flexor digitorum profundus (index and middle fingers)**, and **pronator quadratus**. - Injury to the AIN would result in an inability to form an "OK" sign (due to impaired flexion of the thumb IP joint and index finger DIP joint) and no sensory loss.

Question 30: A 6-year-old boy is brought to the physician because he has a limp for 3 weeks. He was born at term and has been healthy since. His immunization are up-to-date; he received his 5th DTaP vaccine one month ago. He is at 50th percentile for height and weight. His temperature is 37°C (98.6°F), pulse is 80/min and respirations are 28/min. When asked to stand only on his right leg, the left pelvis sags. The remainder of the examination shows no abnormalities. Which of the following is the most likely cause of these findings?

A. L5 radiculopathy
B. Damage to the right common peroneal nerve
C. Damage to the left inferior gluteal nerve
D. Spinal abscess
E. Damage to the right superior gluteal nerve (Correct Answer)

Explanation: ***Damage to the right superior gluteal nerve*** - The patient exhibits a **positive Trendelenburg sign**, where the pelvis drops on the unsupported side (left side) when standing on the affected leg (right side). This indicates weakness of the **contralateral gluteus medius and minimus muscles**, which are innervated by the superior gluteal nerve. - Therefore, damage to the **right superior gluteal nerve** would lead to weakness of the right gluteus medius and minimus, causing the left pelvis to sag when standing on the right leg. *L5 radiculopathy* - L5 radiculopathy would primarily affect muscles innervated by the L5 nerve root, including the **tibialis anterior** (foot dorsiflexion) and **extensor hallucis longus**, which would present differently (e.g., foot drop) rather than isolated gluteal weakness. - While the gluteus medius and minimus receive some innervation from L5, isolated L5 radiculopathy is less likely to cause a pure Trendelenburg gait without other significant neurological deficits. *Damage to the right common peroneal nerve* - Damage to the common peroneal nerve primarily affects muscles of the **anterior and lateral compartments of the leg**, leading to **foot drop** and sensory loss over the dorsum of the foot. - It does not directly innervate the gluteal muscles and therefore would not cause a Trendelenburg gait. *Damage to the left inferior gluteal nerve* - The inferior gluteal nerve innervates the **gluteus maximus**, which is responsible for hip extension. - Damage to the left inferior gluteal nerve would cause weakness in hip extension on the left side, not the characteristic pelvic drop seen with the Trendelenburg sign (which involves the gluteus medius/minimus). *Spinal abscess* - A spinal abscess would typically present with severe back pain, fever, neurological deficits such as motor weakness or sensory loss, and possibly bladder/bowel dysfunction. - While it can cause weakness, it would usually be accompanied by systemic symptoms and more diffuse neurological signs, which are absent in this case.

Question 31: A 61-year-old woman presents to the emergency room with right hand pain and numbness. She was jogging around her neighborhood when she tripped and fell on her outstretched hand 3 hours prior to presentation. She reports severe wrist pain and numbness along the medial aspect of her hand. Her past medical history is notable for osteoporosis and gastroesophageal reflux disease. She takes omeprazole. She has a 10-pack-year smoking history. She has severe tenderness to palpation diffusely around her right wrist. She has decreased sensation to light touch along the palmar medial 2 digits. Sensation to light touch is normal throughout the palm and in the lateral 3 digits. When she is asked to extend all of her fingers, her 4th and 5th fingers are hyperextended at the metacarpophalangeal (MCP) joints and flexed at the interphalangeal (IP) joints. Which of the following nerves is most likely affected in this patient?

A. Posterior interosseous nerve
B. Proximal ulnar nerve
C. Distal median nerve
D. Recurrent branch of the median nerve
E. Distal ulnar nerve (Correct Answer)

Explanation: ***Distal ulnar nerve*** - The patient's symptoms, including numbness along the **medial aspect of the hand** (specifically the 4th and 5th digits), and the characteristic **flexion of the 4th and 5th fingers at the interphalangeal (IP) joints** with hyperextension at the metacarpophalangeal (MCP) joints (known as **ulnar claw**), are highly indicative of distal ulnar nerve injury. - Distal ulnar nerve injury, often seen with trauma to the wrist like a **fall on an outstretched hand**, impacts the intrinsic hand muscles it innervates, leading to this specific **deformity**. *Posterior interosseous nerve* - Injury to the **posterior interosseous nerve** would primarily affect extensor function in the forearm and hand, leading to a **wrist drop** or inability to extend fingers and thumb. - It does not cause sensory deficits in the hand, as it is a **purely motor nerve**. *Proximal ulnar nerve* - A **proximal ulnar nerve** injury (e.g., at the elbow) would cause a more widespread motor deficit, affecting the **flexor carpi ulnaris** and **medial half of the flexor digitorum profundus**, in addition to the intrinsic hand muscles. - Sensory loss would extend to the **dorsal medial hand**, which is not entirely consistent with this patient's presentation. *Distal median nerve* - Injury to the **distal median nerve** (e.g., carpal tunnel syndrome) typically causes sensory loss in the **first three and a half digits** and weakness of **thenar muscles** (e.g., opposition of the thumb). - It would not cause the described ulnar claw deformity of the 4th and 5th fingers. *Recurrent branch of the median nerve* - The **recurrent branch of the median nerve** is a **purely motor nerve** that innervates the **thenar muscles** (abductor pollicis brevis, opponens pollicis, superficial head of flexor pollicis brevis). - Damage to this nerve causes **thenar atrophy** and weakness in thumb opposition, without sensory deficits or effects on the 4th and 5th digits.

Question 32: A 45-year-old man comes to the physician for the evaluation of limited mobility of his right hand for 1 year. The patient states he has had difficulty actively extending his right 4th and 5th fingers, and despite stretching exercises, his symptoms have progressed. He has type 2 diabetes mellitus. He has been working as a mason for over 20 years. His father had similar symptoms and was treated surgically. The patient has smoked one pack of cigarettes daily for 25 years and drinks 2–3 beers every day after work. His only medication is metformin. Vital signs are within normal limits. Physical examination shows skin puckering near the proximal flexor crease. There are several painless palmar nodules adjacent to the distal palmar crease. Active and passive extension of the 4th and 5th digits of the right hand is limited. Which of the following is the most likely underlying mechanism of this patient's symptoms?

A. Ulnar nerve lesion
B. Ganglion cyst
C. Palmar fibromatosis (Correct Answer)
D. Tendon sheath tumor
E. Tenosynovitis

Explanation: ***Palmar fibromatosis*** - The patient's symptoms, including **painless palmar nodules**, skin puckering near the flexor crease, and inability to actively extend the 4th and 5th fingers (a classic presentation of **Dupuytren's contracture**), are indicative of palmar fibromatosis. - Risk factors like **male sex**, **age > 40**, **smoking**, **alcohol use**, **diabetes mellitus**, and a **family history** of similar symptoms are all present in this patient, strongly supporting the diagnosis. *Ulnar nerve lesion* - An ulnar nerve lesion would primarily cause **sensory deficits** (numbness/tingling in the 4th and 5th digits) and **motor weakness** in intrinsic hand muscles, leading to a **claw hand deformity**, not typically the presence of palmar nodules or skin puckering. - While it can affect the 4th and 5th digits, the mechanism of limitation would be due to muscle weakness rather than fixed contracture. *Ganglion cyst* - A ganglion cyst is a **fluid-filled sac** that typically presents as a smooth, mobile, sometimes painful lump, often on the dorsal aspect of the wrist or fingers. - It does not cause progressive finger contracture, skin puckering, or diffuse palmar nodules. *Tendon sheath tumor* - A tendon sheath tumor (e.g., giant cell tumor of the tendon sheath) is a **benign soft tissue mass** that presents as a firm, localized nodule, usually associated with a tendon. - While it can limit finger movement, it typically does so by mass effect and does not cause the characteristic diffuse fibrotic changes and skin puckering seen in Dupuytren's contracture. *Tenosynovitis* - Tenosynovitis is **inflammation of the tendon sheath**, often causing pain, swelling, and tenderness along the course of the tendon, and sometimes a "triggering" sensation with movement. - It does not typically manifest as painless, firm palmar nodules or progressive contracture with skin puckering.

Question 33: A 17-year-old teenager is brought to the emergency department with severe bleeding from his right hand. He was involved in a gang fight about 30 minutes ago where he received a penetrating stab wound by a sharp knife in the region of the ‘anatomical snuffbox’. A vascular surgeon is called in for consultation. Damage to which artery is most likely responsible for his excessive bleeding?

A. Ulnar artery
B. Palmar carpal arch
C. Radial artery (Correct Answer)
D. Princeps pollicis artery
E. Brachial artery

Explanation: ***Radial artery*** - The **anatomical snuffbox** is formed by the tendons of the **extensor pollicis longus**, **extensor pollicis brevis**, and **abductor pollicis longus**. The floor of this region is primarily formed by the **scaphoid** and **trapezial bones**. - The **radial artery** passes directly through the anatomical snuffbox to contribute to the deep palmar arch. A penetrating injury in this area would most likely damage the radial artery, leading to significant bleeding. *Ulnar artery* - The **ulnar artery** runs along the medial side of the forearm and enters the hand superficial to the **flexor retinaculum**, lateral to the ulnar nerve. - It does not pass through the **anatomical snuffbox**. *Palmar carpal arch* - The **palmar carpal arches** are anastomoses between the radial and ulnar arteries on the palmar aspect of the wrist. - While they are in the vicinity, a direct stab in the **anatomical snuffbox** specifically targets the radial artery as it traverses this area. *Princeps pollicis artery* - The **princeps pollicis artery** is a branch of the **radial artery** that supplies the thumb. - While it originates from the radial artery, the primary vessel at risk within the **anatomical snuffbox** itself, causing systemic excessive bleeding, is the main trunk of the radial artery before it gives off this specific branch. *Brachial artery* - The **brachial artery** is located in the arm and terminates in the cubital fossa, dividing into the radial and ulnar arteries. - It is too proximal to be injured by a stab wound to the **anatomical snuffbox** in the hand.

Question 34: A 20-year-old man comes to the clinic complaining of shoulder pain for the past week. He is a pitcher for the baseball team at his university and reports that the pain started shortly after a game. The pain is described as achy and dull, intermittent, 7/10, and is concentrated around the right shoulder area. He denies any significant medical history, trauma, fever, recent illness, or sensory changes but endorses some difficulty lifting his right arm. A physical examination demonstrates mild tenderness of the right shoulder. When the patient is instructed to resist arm depression when holding his arms parallel to the floor with the thumbs pointing down, he reports significant pain of the right shoulder. Strength is 4/5 on the right and 5/5 on the left with abduction of the upper extremities. What nerve innervates the injured muscle in this patient?

A. Axillary nerve
B. Long thoracic nerve
C. Subscapular nerve
D. Accessory nerve
E. Suprascapular nerve (Correct Answer)

Explanation: ***Suprascapular nerve*** - The patient's symptoms, including shoulder pain exacerbated by the "empty can" test (resisted arm depression with thumbs down), are highly suggestive of a rotator cuff injury, specifically involving the supraspinatus muscle. - The suprascapular nerve innervates both the supraspinatus and infraspinatus muscles, which are critical for shoulder abduction and external rotation. *Axillary nerve* - The axillary nerve innervates the deltoid muscle and the teres minor muscle. - Injury to the axillary nerve or these muscles would primarily affect shoulder abduction beyond the initial 15 degrees and external rotation, but the "empty can" test specifically targets the supraspinatus. *Long thoracic nerve* - The long thoracic nerve innervates the serratus anterior muscle, which is responsible for scapular protraction and upward rotation. - Damage to this nerve typically presents with "winged scapula," which is not indicated in this case. *Subscapular nerve* - The subscapular nerve innervates the subscapularis muscle (upper and lower subscapular nerves), which is a key internal rotator of the shoulder. - While it's a rotator cuff muscle, injury to the subscapularis would primarily manifest as difficulty with internal rotation, not typically identified by the "empty can" test. *Accessory nerve* - The accessory nerve (cranial nerve XI) innervates the sternocleidomastoid and trapezius muscles. - Injury to this nerve would result in difficulty shrugging the shoulders or turning the head, not pain related to rotator cuff function.

Question 35: A 72-year-old woman presents to the emergency department complaining of left gluteal pain for the last 3 months. The onset of the pain was gradual and she does not recall any trauma to the region. She describes the pain as sharp and progressive, with radiation down the posterior left thigh to the level of the knee. She is a non-smoker without a history of anticoagulant therapy. Her past medical history is significant for peripheral vascular disease, hypertension, and hyperlipidemia. The physical examination focusing on the left gluteal region reveals atrophy and muscle weakness. The blood cell count and blood chemistry profile are within normal limits. The suspected embolus was confirmed with a pelvic computed tomography scan demonstrating a heterogeneously-enhanced blockage in the deep branch of the superior gluteal artery. The patient underwent an uneventful super-selective embolization and recovered well. Complete occlusion of this artery may cause muscle ischemia and atrophy that would compromise the ability to perform which of the following actions?

A. Climbing stairs
B. Walking (Correct Answer)
C. Rise from a sitting position
D. Standing
E. Running

Explanation: ***Walking*** - The **superior gluteal artery** supplies the **gluteus medius** and **minimus** muscles, which are crucial for **pelvic stability** during the swing phase of walking. - Atrophy and weakness of these muscles due to ischemia would directly impair the ability to maintain a level pelvis, leading to a **Trendelenburg gait** and difficulty with walking. *Climbing stairs* - While climbing stairs utilizes gluteal muscles, the primary movers are the **gluteus maximus** and quadriceps. - The superior gluteal artery mainly affects gluteus medius and minimus, which are more involved in abduction and internal rotation for pelvic stability rather than the powerful hip extension needed for stair climbing. *Rise from a sitting position* - Rising from a sitting position primarily involves the **gluteus maximus** and quadriceps for powerful hip extension and knee extension. - The superior gluteal artery embolus impacts the gluteus medius and minimus, which are less central to this action compared to the gluteus maximus. *Standing* - Standing upright requires core stability and calf muscle activity, with the gluteal muscles playing a secondary role in maintaining hip extension. - While the gluteus medius and minimus contribute to pelvic stability, severe inability to stand would be more indicative of issues with major extensor muscles or neurological deficits. *Running* - Running involves a complex interplay of many muscle groups, including powerful hip extension from the gluteus maximus and strong quadriceps and hamstring action. - While **gluteus medius** and **minimus** are important for hip abduction and stability during running, their isolated compromise (as described) would more significantly impact the more fundamental, continuous act of walking.

Question 36: A 12-year-old boy presents to the emergency department after falling from his bike. He is holding his right arm tenderly and complains of pain in his right wrist. When asked, he says that he fell after his front tire hit a rock and landed hard on his right hand. Upon physical examination he is found to have tenderness on the dorsal aspect of his wrist in between the extensor pollicis longus and the extensor pollicis brevis. Given this presentation, which of the following is the most likely bone to have been fractured?

A. Pisiform
B. Scaphoid (Correct Answer)
C. Lunate
D. Capitate
E. Trapezoid

Explanation: ***Scaphoid*** - The mechanism of injury (**fall on an outstretched hand**) and the location of tenderness (**dorsal aspect of the wrist between the extensor pollicis longus and extensor pollicis brevis**, which corresponds to the **anatomical snuffbox**) are classic signs of a scaphoid fracture. - The **scaphoid** is the most commonly fractured carpal bone and its fracture can lead to **avascular necrosis** due to its retrograde blood supply if not properly managed. *Pisiform* - Fractures of the **pisiform** are rare and typically result from direct trauma to the hypothenar eminence, not from a fall on an outstretched hand. - Pain would be localized to the **ulnar side of the wrist**, distinct from the anatomical snuffbox. *Lunate* - A **lunate fracture** is rare and usually associated with high-energy trauma, often leading to **Kienbock's disease** (avascular necrosis of the lunate). - Tenderness would be more centrally located on the dorsal aspect of the wrist, not specifically within the anatomical snuffbox. *Capitate* - **Capitate fractures** are uncommon and often occur in conjunction with other carpal injuries due to its central and protected position. - Pain and tenderness would be more diffuse in the midcarpal region rather than localized to the anatomical snuffbox. *Trapezoid* - **Trapezoid fractures** are very rare and typically result from axial loading force through the second metacarpal. - Tenderness would be located more distally, at the base of the **second metacarpal**, not within the anatomical snuffbox.

Question 37: A 36-year-old woman comes to the physician because of new onset limping. For the past 2 weeks, she has had a tendency to trip over her left foot unless she lifts her left leg higher while walking. She has not had any trauma to the leg. She works as a flight attendant and wears compression stockings to work. Her vital signs are within normal limits. Physical examination shows weakness of left foot dorsiflexion against minimal resistance. There is reduced sensation to light touch over the dorsum of the left foot, including the web space between the 1st and 2nd digit. Further evaluation is most likely to show which of the following?

A. Decreased ankle jerk reflex
B. Normal foot eversion
C. Weak knee flexion
D. Normal foot inversion (Correct Answer)
E. Weak hip flexion

Explanation: ***Normal foot inversion*** - The patient's symptoms of **foot drop** and **sensory loss** on the dorsum of the foot, including the web space between the 1st and 2nd digits, point to an injury of the **common fibular (peroneal) nerve** or its deep branch. - The **deep fibular nerve** innervates the muscles responsible for **dorsiflexion** (tibialis anterior, extensor digitorum longus, extensor hallucis longus) and provides sensation to the **first dorsal web space**. The **superficial fibular nerve** innervates muscles for **eversion** and provides sensation to the rest of the foot dorsum. The **tibial nerve** innervates muscles for **foot inversion** (tibialis posterior) and plantarflexion; because the fibular nerve is affected, **tibial nerve function**, including foot inversion, should remain intact. *Decreased ankle jerk reflex* - The **ankle jerk reflex** (achilles tendon reflex) primarily tests the S1 nerve root, mediated by the **tibial nerve**. - A common fibular nerve lesion does not directly affect the tibial nerve, thus the **ankle jerk reflex** is expected to be normal. *Normal foot eversion* - **Foot eversion** is primarily mediated by the **peroneus longus** and **brevis muscles**, which are supplied by the **superficial fibular nerve**. - A lesion of the common fibular nerve before its bifurcation would affect both the deep and superficial branches, leading to **weakness or absence of foot eversion**. *Weak knee flexion* - **Knee flexion** is primarily controlled by the **hamstring muscles** (semitendinosus, semimembranosus, biceps femoris), which are innervated by the **tibial nerve** and the **common fibular nerve's branch to the short head of the biceps femoris**. - While the common fibular nerve does contribute to biceps femoris innervation, the primary muscles for knee flexion are supplied by the tibial nerve, and isolated common fibular nerve injury typically does not result in significant global knee flexion weakness. *Weak hip flexion* - **Hip flexion** is primarily performed by the **iliopsoas muscle**, which is innervated by the **femoral nerve** and direct branches from the lumbar plexus (L1-L3). - Injury to the common fibular nerve, which is a branch of the sciatic nerve (L4-S2), does not affect the innervation of the **hip flexors**.

Question 38: A 16-year-old boy presents to the emergency room with severe right shoulder pain following a painful overhead swing during a competitive volleyball match. On physical examination, the patient has limited active range of motion of the right shoulder and significant pain with passive motion. Suspecting a rotator cuff injury, the physician obtains an MRI, which indicates a minor tear in the tendon of the rotator cuff muscle that is innervated by the axillary nerve. Which of the following muscles was affected?

A. Teres major
B. Supraspinatus
C. Teres minor (Correct Answer)
D. Infraspinatus
E. Subscapularis

Explanation: ***Correct: Teres minor*** - **Teres minor** is the only rotator cuff muscle innervated by the **axillary nerve** (C5-C6) - Functions as an **external rotator** of the shoulder and stabilizes the humeral head - The axillary nerve courses through the **quadrangular space** (bordered by teres minor superiorly, teres major inferiorly, long head of triceps medially, and surgical neck of humerus laterally) - Injury to this muscle can occur with overhead activities, though less commonly injured than supraspinatus *Incorrect: Supraspinatus* - Innervated by the **suprascapular nerve** (C5-C6), not the axillary nerve - Most commonly injured rotator cuff muscle, particularly with overhead activities - Functions primarily in **abduction** (initiates first 15° of abduction) *Incorrect: Infraspinatus* - Innervated by the **suprascapular nerve** (C5-C6), not the axillary nerve - Functions as the primary **external rotator** of the shoulder - Second most commonly injured rotator cuff muscle *Incorrect: Subscapularis* - Innervated by the **upper and lower subscapular nerves** (C5-C7), not the axillary nerve - Only rotator cuff muscle on the **anterior** surface of the scapula - Functions as an **internal rotator** of the shoulder *Incorrect: Teres major* - **NOT part of the rotator cuff** (forms part of the posterior axillary fold) - Innervated by the **lower subscapular nerve** (C5-C7), not the axillary nerve - Functions as an **internal rotator, adductor, and extensor** of the shoulder

Question 39: A 35-year-old man is brought to the trauma bay by ambulance after sustaining a gunshot wound to the right arm. The patient is in excruciating pain and states that he can't move or feel his hand. The patient states that he has no other medical conditions. On exam, the patient's temperature is 98.4°F (36.9°C), blood pressure is 140/86 mmHg, pulse is 112/min, and respirations are 14/min. The patient is alert and his Glasgow coma scale is 15. On exam, he has a single wound on his right forearm without continued bleeding. The patient has preserved motor and sensation in his right elbow; however, he is unable to extend his wrist or extend his fingers further. He is able to clench his hand, but this is limited by pain. On sensory exam, the patient has no sensation to the first dorsal web space but has preserved sensation on most of the volar surface. Which of the following structures is most likely injured?

A. Recurrent motor branch of the median nerve
B. Main median nerve
C. Lower trunk
D. Ulnar nerve
E. Radial nerve (Correct Answer)

Explanation: ***Radial nerve*** - The inability to **extend the wrist and fingers** (wrist drop) is a classic sign of **radial nerve injury**, as it innervates the extensors of the forearm and hand. - **Loss of sensation in the first dorsal web space** is also characteristic of radial nerve damage, as this area is supplied by the superficial radial nerve. *Recurrent motor branch of the median nerve* - This nerve primarily innervates the **thenar muscles** (flexor pollicis brevis, abductor pollicis brevis, opponens pollicis), affecting **thumb opposition**. - Injury would primarily lead to **weakness in thumb movements**, not wrist or finger extension, and would spare sensation in the first dorsal web space. *Main median nerve* - The median nerve primarily innervates the **flexors of the forearm and hand**, and contributes to sensation on the **volar aspect of the thumb**, index, middle, and radial half of the ring finger. - Injury would cause difficulty with **flexion of the wrist and fingers**, and loss of sensation on the volar surface, which is largely preserved in this patient. *Lower trunk* - The lower trunk of the brachial plexus (C8-T1) gives rise to the ulnar nerve and part of the median nerve, affecting **flexion of the wrist and fingers**, and intrinsic hand muscles. - Injury would result in more widespread weakness affecting the **intrinsic hand muscles** and flexion, and would include sensory loss in the **ulnar nerve distribution**, which is not described. *Ulnar nerve* - The ulnar nerve primarily innervates the **intrinsic hand muscles** (excluding the thenar group) and the **flexor carpi ulnaris** and **medial half of flexor digitorum profundus**. - Injury would typically cause **weakness in intrinsic hand functions** (e.g., finger abduction/adduction, ring and little finger flexion) and sensory loss on the **ulnar side of the hand**, not the dorsal web space.

Question 40: A 27-year-old female ultramarathon runner presents to the physician with complaints of persistent knee pain. She describes the pain to be located in the anterior area of her knee and is most aggravated when she performs steep descents down mountains, though the pain is present with running on flat roads, walking up and down stairs, and squatting. Which of the following would most likely be an additional finding in this patient’s physical examination?

A. Pain upon pressure placed on the lateral aspect of the knee
B. Pain upon pressure placed on the medial aspect of the knee
C. Pain upon compression of the patella while the patient performs flexion and extension of the leg (Correct Answer)
D. Excessive posterior displacement of the tibia
E. Excessive anterior displacement of the tibia

Explanation: ***Pain upon compression of the patella while the patient performs flexion and extension of the leg*** - The patient's symptoms (anterior knee pain aggravated by activity, especially descents, stairs, and squatting) are classic for **patellofemoral pain syndrome (runner's knee)**. - The **patellofemoral grind test** (compressing the patella during knee flexion and extension) is a specific diagnostic maneuver that reproduces this pain in affected individuals. *Pain upon pressure placed on the lateral aspect of the knee* - This finding is more characteristic of conditions like **iliotibial band syndrome** or **lateral meniscus injury**, which typically present with lateral knee pain. - The patient describes general anterior knee pain, not specifically lateral pain. *Pain upon pressure placed on the medial aspect of the knee* - This suggests conditions such as **medial collateral ligament (MCL) injury**, **pes anserine bursitis**, or **medial meniscus injury**. - These conditions typically present with medial knee pain, which does not match the patient's anterior knee pain. *Excessive posterior displacement of the tibia* - This indicates **posterior cruciate ligament (PCL) insufficiency**, which is assessed by the posterior drawer test or sag sign. - PCL injuries typically result from direct trauma to the anterior tibia or hyperflexion, and pain is often localized posteriorly or deep within the knee, not specifically anteriorly aggravated by the described activities. *Excessive anterior displacement of the tibia* - This finding is indicative of an **anterior cruciate ligament (ACL) rupture**, assessed by the Lachman test or anterior drawer test. - ACL injuries usually result from a twisting injury or hyperextension and often present with acute swelling, instability, and giving way, which are not the primary complaints of this patient with chronic, activity-related anterior knee pain.

Question 41: A 57-year-old man presents to the ED complaining of back and left leg pain. He was lifting heavy furniture while helping his daughter move into college when all of sudden he felt a sharp pain at his back. The pain is described as severe, worse with movement, and shoots down his lateral thigh. The patient denies any bowel/urinary incontinence, saddle anesthesia, weight loss, or weakness. He denies any past medical history but endorses a family history of osteoporosis. He has been smoking 1 pack per day for the past 20 years. Physical examination demonstrated decreased sensation at the left knee, decreased patellar reflex, and a positive straight leg test. There is diffuse tenderness to palpation at the lower back but no vertebral step-offs were detected. What is the most likely etiology for this patient’s pain?

A. Vertebral compression fracture
B. Disc herniation at the L4/L5 vertebra
C. Spinal metastasis from lung cancer
D. Disc herniation at the L3/L4 vertebra (Correct Answer)
E. Lumbar muscle sprain

Explanation: ***Disc herniation at the L3/L4 vertebra*** - The patient's symptoms of **acute back pain radiating down the lateral thigh** after lifting, combined with **decreased sensation at the left knee** and a **decreased patellar reflex**, are classic signs of L3/L4 nerve root compression. - A **positive straight leg test** also supports nerve root irritation, and the absence of red flag symptoms like incontinence or saddle anesthesia makes a simple disc herniation more likely than other serious conditions. *Vertebral compression fracture* - While lifting heavy objects can cause compression fractures, these usually present with more **severe, localized pain** that is not typically radiating with specific dermatomal or reflex changes. - Absence of **vertebral step-offs** or significant predisposing factors for a fracture (e.g., severe osteoporosis, trauma) makes this less likely given the specific neurological findings. *Disc herniation at the L4/L5 vertebra* - An L4/L5 disc herniation would typically cause symptoms related to the **L5 nerve root**, such as pain radiating down the **lateral leg into the foot**, **weakness in dorsiflexion of the ankle** or **big toe**, and potentially a **decreased medial hamstring reflex**. - The patient's reported symptoms (lateral thigh pain, decreased knee sensation, decreased patellar reflex) are more consistent with **L4 nerve root** involvement. *Spinal metastasis from lung cancer* - Although the patient has a **smoking history** and could be at risk for lung cancer, this diagnosis typically presents with more **insidious onset** of unexplained back pain, often with **weight loss**, and sometimes with more profound neurological deficits or bone pain not relieved by rest. - The acute onset after an inciting event and specific neurological findings of a single nerve root are less suggestive of metastasis. *Lumbar muscle sprain* - A muscle sprain would typically present with **localized back pain**, often worsened by movement, but would **not involve radicular pain** shooting down the leg, nor would it cause specific **neurological deficits** like decreased sensation or reflex changes. - The positive straight leg test and neurological findings rule out a simple muscle sprain.

Question 42: A 46-year-old man is brought to the emergency department for the onset of severe pain in his right knee that occurred when he tripped while descending a staircase. As he landed, he heard and felt an immediate popping sensation in his right knee. His medical history is positive for obesity, hypertension, type 2 diabetes mellitus, severe asthma, and hyperlipidemia. He currently takes lisinopril, hydrochlorothiazide, metformin, atorvastatin, an albuterol inhaler, and a fluticasone inhaler. He recently completed a hospitalization and week-long regimen of systemic corticosteroids for a severe exacerbation of his asthma. The patient's family history is not significant. In the emergency department, his vital signs are normal. On physical examination, his right knee is warm and swollen and he rates the pain as 9/10. He cannot stand or walk due to pain. He is unable to extend his right knee. A knee X-ray is ordered. Which of the following would best describe the cause of this presenting condition?

A. Quadriceps tendon tear (Correct Answer)
B. Meniscal tear
C. Avascular necrosis of the femur
D. Traction apophysitis of the tibia
E. Femoral fracture

Explanation: ***Quadriceps tendon tear*** - The patient's inability to **extend his right knee**, along with the history of a "pop" and severe pain after a fall, is highly indicative of a quadriceps tendon tear. - The quadriceps tendon connects the quadriceps muscle group to the patella, and rupture results in loss of active knee extension—patients cannot perform a straight leg raise. - Recent use of **systemic corticosteroids** can weaken tendons, predisposing individuals to such injuries, especially during a forceful eccentric contraction like catching oneself during a fall. - Classic physical exam findings include a palpable **suprapatellar gap** and inability to extend the knee against gravity. *Meniscal tear* - While a meniscal tear can cause sudden knee pain and a popping sensation, it typically doesn't result in a complete inability to **extend the knee actively**. - Patients with meniscal tears often present with mechanical symptoms like **locking, catching, or clicking**, which are not described here. - Range of motion may be limited by pain or mechanical block, but the extensor mechanism remains intact. *Avascular necrosis of the femur* - This condition involves the death of bone tissue due to disrupted blood supply, often causing **gradual onset pain** that worsens with weight-bearing over weeks to months. - Risk factors include chronic corticosteroid use, but it does not typically present with an acute "pop" and immediate functional loss after a traumatic event like a fall. - Imaging would show collapse of the femoral head, not an acute soft tissue injury. *Traction apophysitis of the tibia* - Traction apophysitis (e.g., Osgood-Schlatter disease) is an **overuse injury** commonly seen in adolescents due to repetitive stress on the tibial tuberosity growth plate. - It presents with gradual onset anterior knee pain and does not explain the acute onset of severe pain and inability to extend the knee in a 46-year-old man after a fall. - This is a pediatric/adolescent condition, not seen in middle-aged adults with closed growth plates. *Femoral fracture* - A femoral fracture would cause severe pain and inability to bear weight, but the primary deficit would be the inability to move the entire leg due to bone instability and severe pain. - The specific, isolated deficit in **active knee extension** with preservation of passive range of motion points to a disruption of the extensor mechanism (tendon injury) rather than a bone fracture. - X-ray would show obvious fracture line in the femoral shaft or neck, which would be a more dramatic presentation.

Question 43: An 80-year-old woman is brought to the emergency department for left hip pain 30 minutes after she fell while walking around in her room. Examination shows left groin tenderness. The range of motion of the left hip is limited because of pain. An x-ray of the hip shows a linear fracture of the left femoral neck with slight posterior displacement of the femur. Which of the following arteries was most likely damaged in the patient's fall?

A. Superior gluteal artery
B. Deep circumflex iliac
C. Deep femoral artery
D. Obturator
E. Medial circumflex femoral (Correct Answer)

Explanation: ***Medial circumflex femoral*** - This artery is the **primary blood supply** to the femoral head and neck, making it highly vulnerable to injury in cases of femoral neck fractures. - Damage to the medial circumflex femoral artery significantly increases the risk of **avascular necrosis** of the femoral head. *Superior gluteal artery* - The superior gluteal artery primarily supplies the **gluteus medius** and **minimus muscles**. - It is **not directly involved** in the primary blood supply to the femoral head and neck. *Deep circumflex iliac* - This artery mainly supplies the **iliac fossa** and the **abdominal wall muscles**. - It does not contribute significantly to the blood supply of the femoral neck. *Deep femoral artery* - The deep femoral artery, also known as the **profunda femoris artery**, is the main supply to the **thigh muscles**. - While it gives rise to the circumflex arteries, it is not the artery directly compromised in a femoral neck fracture. *Obturator* - The obturator artery primarily supplies the **adductor muscles** of the thigh and contributes a small branch to the femoral head via the **ligamentum teres**. - This contribution is **insufficient** to maintain viability of the femoral head, especially in trauma to the femoral neck.

Question 44: A 32-year-old man comes to the physician because of a 1-month history of intermittent tingling of his hand. He is an avid cyclist and has recently started training for a cycle marathon. Physical examination shows decreased grip strength in the right hand and wasting of the hypothenar eminence. On asking the patient to grasp a piece of paper between his right thumb and right index finger in the first web space, there is hyperflexion of the right thumb interphalangeal joint. Which of the following additional findings is most likely in this patient?

A. Loss of sensation over the dorsum of the medial half of the hand
B. Inability to extend the ring finger at the metacarpophalangeal joint
C. Inability to flex the index finger at the interphalangeal joints
D. Loss of sensation over the palmar aspect of the middle finger
E. Inability to extend the little finger at the proximal interphalangeal joints (Correct Answer)

Explanation: ***Inability to extend the little finger at the proximal interphalangeal joints*** - The patient's symptoms (tingling, decreased grip strength, hypothenar eminence wasting, and **Froment's sign**) indicate **ulnar nerve compression at Guyon's canal** (handlebar palsy) from cycling. - The ulnar nerve innervates the **3rd and 4th lumbricals** (medial two), which extend the PIP and DIP joints of the ring and little fingers. - The ulnar nerve also innervates the **interossei muscles**, which assist in MCP flexion and IP extension. - Loss of these intrinsic muscles results in **claw hand deformity** affecting the 4th and 5th digits, with hyperextension at MCP joints and flexion (inability to extend) at PIP and DIP joints. - This is a classic finding in ulnar nerve palsy. *Inability to extend the ring finger at the metacarpophalangeal joint* - Extension at the MCP joint is primarily performed by the **extensor digitorum** (innervated by the **radial nerve**). - The patient's findings indicate ulnar nerve compression, not radial nerve injury. - In ulnar nerve palsy, the unopposed extensor digitorum actually causes MCP **hyperextension**, not inability to extend. *Inability to flex the index finger at the interphalangeal joints* - Flexion of the index finger IP joints is controlled by **flexor digitorum superficialis** (FDS) and **flexor digitorum profundus** (FDP). - Both muscles to the index finger are innervated by the **median nerve**, not the ulnar nerve. - This finding would indicate median nerve injury (e.g., carpal tunnel syndrome or anterior interosseous syndrome). *Loss of sensation over the palmar aspect of the middle finger* - Palmar sensation of the middle finger is supplied by the **median nerve**. - The ulnar nerve supplies sensation to the medial 1.5 digits (little finger and medial half of ring finger). - This finding would indicate median nerve pathology, not ulnar nerve compression. *Loss of sensation over the dorsum of the medial half of the hand* - The **dorsal cutaneous branch of the ulnar nerve** branches approximately 5-8 cm proximal to the wrist and passes **superficially**, NOT through Guyon's canal. - In **Guyon's canal compression** (handlebar palsy), the dorsal cutaneous branch is **SPARED**, so dorsal sensation remains intact. - The patient would have palmar sensory loss over the medial 1.5 digits but **preserved dorsal sensation**. - Loss of dorsal sensation would suggest a more proximal ulnar nerve lesion (at the elbow or forearm), not at the wrist.

Question 45: A 40-year-old male presents to the physician's office complaining of an inability to push doors open. He has had this problem since he was playing football with his children and was tackled underneath his right arm on his lateral chest. On examination, he has a winged scapula on the right side. Which of the following nerves is most likely the cause of this presentation?

A. Phrenic nerve
B. Spinal accessory nerve
C. Long thoracic nerve (Correct Answer)
D. Greater auricular nerve
E. Musculocutaneous nerve

Explanation: ***Long thoracic nerve*** - The **long thoracic nerve** innervates the **serratus anterior muscle**, which is responsible for scapular protraction and upward rotation. - Damage to this nerve, often from trauma to the lateral chest wall (tackled underneath the arm), leads to paralysis of the serratus anterior and a characteristic **winged scapula** with lateral and inferior prominence. - Patients have difficulty with **pushing movements** (protraction) and overhead activities. *Phrenic nerve* - The **phrenic nerve** primarily innervates the **diaphragm** and is crucial for respiration. - Damage to the phrenic nerve would cause respiratory compromise, not a winged scapula or difficulty pushing doors. *Spinal accessory nerve* - The **spinal accessory nerve (cranial nerve XI)** innervates the **sternocleidomastoid** and **trapezius muscles**. - Injury to this nerve can cause scapular winging due to **trapezius paralysis**, but the winging is typically **medial** with the inferior angle moving medially, unlike the lateral winging from serratus anterior paralysis. - The mechanism of injury (lateral chest trauma during tackling) and inability to push are classic for **long thoracic nerve** injury, not spinal accessory nerve. *Greater auricular nerve* - The **greater auricular nerve** is a cutaneous nerve that provides sensation to the skin over the parotid gland, mastoid process, and auricle. - Damage to this nerve would result in sensory loss in these areas and is unrelated to muscle weakness or a winged scapula. *Musculocutaneous nerve* - The **musculocutaneous nerve** innervates the **biceps brachii**, **brachialis**, and **coracobrachialis muscles**, responsible for elbow flexion and forearm supination. - Damage to this nerve would primarily affect these movements and sensation in the lateral forearm, not leading to a winged scapula.

Question 46: A 31-year-old woman with multiple sclerosis comes to the physician because of a 4-day history of cramps in her left leg. Physical examination shows flexion of the left hip and increased tone in the thigh muscles. A local anesthetic block of which of the following nerves would most likely improve this patient's condition the most?

A. Inferior gluteal nerve
B. Superior gluteal nerve
C. Femoral nerve (Correct Answer)
D. Sciatic nerve
E. Obturator nerve

Explanation: ***Femoral nerve*** - The **femoral nerve** innervates the **iliacus** (a primary hip flexor) and the **rectus femoris** (part of the quadriceps that assists in hip flexion), as well as the entire **quadriceps femoris group** (responsible for knee extension and contributing to increased thigh muscle tone). - In this patient with spasticity, **hip flexion** is caused by hypertonicity of iliopsoas and rectus femoris, while **increased tone in thigh muscles** reflects quadriceps involvement. - Blocking the femoral nerve would relax these muscles, thereby improving the **cramps, hip flexion, and increased thigh tone**. *Inferior gluteal nerve* - The **inferior gluteal nerve** primarily innervates the **gluteus maximus muscle**, which is involved in hip extension and external rotation, not hip flexion. - Blocking this nerve would not directly address the symptoms of increased thigh muscle tone and hip flexion. *Superior gluteal nerve* - The **superior gluteal nerve** mainly innervates the **gluteus medius, gluteus minimus**, and **tensor fasciae latae muscles**, which are involved in hip abduction and internal rotation. - Its blockade would not relieve hip flexion or thigh muscle cramps. *Sciatic nerve* - The **sciatic nerve** innervates the **hamstring muscles** (hip extension, knee flexion) and all muscles below the knee. - While it affects leg muscles, it does not directly control the muscles causing **hip flexion and increased thigh tone** in this context. *Obturator nerve* - The **obturator nerve** primarily innervates the **adductor muscles** of the thigh (adductor longus, brevis, magnus, gracilis), leading to hip adduction. - Blocking this nerve would not address hip flexion or the increased tone in the quadriceps muscles described.

Question 47: A 28-year-old woman presents to the emergency department with lateral knee pain that started this morning. The patient is a college student who is currently on the basketball team. She states her pain started after she twisted her knee. Her current medications include albuterol and ibuprofen. The patient's vitals are within normal limits and physical exam is notable for tenderness to palpation over the lateral right knee. When the patient lays on her left side and her right hip is extended and abducted it does not lower to the table in a smooth fashion and adduction causes discomfort. The rest of her exam is within normal limits. Which of the following is the most likely diagnosis?

A. Musculoskeletal strain
B. Pes anserine bursitis
C. Lateral collateral ligament injury
D. Patellofemoral syndrome
E. Iliotibial band syndrome (Correct Answer)

Explanation: ***Iliotibial band syndrome*** - This condition is characterized by **lateral knee pain** in athletes, exacerbated by activity, and often associated with a positive **Ober's test** (inability of the abducted leg to lower to the table smoothly). - The patient's history of **twisting her knee** during basketball and the specific physical exam finding are highly indicative of IT band irritation. *Musculoskeletal strain* - While a strain could cause pain, it typically wouldn't present with the specific **Ober's test findings** that point towards IT band pathology. - A strain would generally exhibit diffuse tenderness rather than localized tenderness over the **lateral epicondyle** or IT band insertion. *Pes anserine bursitis* - This condition causes pain on the **medial side of the knee**, not the lateral side as described in the patient's presentation. - It involves inflammation of the bursa located below the knee on the inner aspect, where the **sartorius, gracilis, and semitendinosus tendons** insert. *Lateral collateral ligament injury* - An LCL injury typically results from a **varus stress** to the knee and presents with pain and instability on the **lateral aspect of the knee**. - While there might be lateral tenderness, an LCL injury would not typically cause the **tightness and discomfort noted with hip adduction** and a positive Ober's test. *Patellofemoral syndrome* - This condition causes **anterior knee pain** around or behind the kneecap, often worsened by activities like climbing stairs or prolonged sitting. - The patient's pain is specifically described as **lateral knee pain**, and the physical exam findings are not typical for patellofemoral syndrome.

Question 48: A 23-year-old woman presents to the emergency department with an acute exacerbation of her 3-month history of low back and right leg pain. She says she has had similar symptoms in the past, but this time the pain was so excruciating, it took her breath away. She describes the pain as severe, shock-like, and localized to her lower back and radiating straight down the back of her right thigh and to her calf, stopping at the ankle. Her pain is worse in the morning, and, sometimes, the pain wakes her up at night with severe buttock and posterior thigh pain but walking actually makes the pain subside somewhat. The patient reports no smoking history or alcohol or drug use. She has been working casually as a waitress and does find bending over tables a strain. She is afebrile, and her vital signs are within normal limits. On physical examination, her left straight leg raise test is severely limited and reproduces her buttock pain at 20° of hip flexion. Pain is worsened by the addition of ankle dorsiflexion. The sensation is intact. Her L4 and L5 reflexes are normal, but her S1 reflex is absent on the right side. A CT of the lumbar spine shows an L5–S1 disc protrusion with right S1 nerve root compression. Which of the following muscle-nerve complexes is involved in producing an S1 reflex?

A. Adductors-obturator nerve
B. Gastrocnemius/soleus-tibial nerve (Correct Answer)
C. Sartorius-femoral nerve
D. Tibialis posterior-tibial nerve
E. Quadriceps femoris-femoral nerve

Explanation: ***Gastrocnemius/soleus-tibial nerve*** - The S1 reflex (also known as the **Achilles reflex**) tests the integrity of the **S1 nerve root**. - This reflex arc involves the **gastrocnemius and soleus muscles**, which are innervated by the **tibial nerve** (derived primarily from S1). *Adductors-obturator nerve* - The **adductor muscles** of the thigh are primarily innervated by the **obturator nerve** (L2-L4). - This complex is not involved in generating the **Achilles reflex**. *Sartorius-femoral nerve* - The **sartorius muscle** is innervated by the **femoral nerve** (L2-L4). - This muscle and nerve are not part of the **S1 reflex arc**. *Tibialis posterior-tibial nerve* - The **tibialis posterior muscle** is innervated by the **tibial nerve** (L4-S3), but its primary role is in ankle inversion and plantarflexion, not the main component of the **Achilles reflex**. - While the tibial nerve is involved in the S1 reflex, the **gastrocnemius and soleus** are the primary muscles for this reflex. *Quadriceps femoris-femoral nerve* - The **quadriceps femoris muscle** is responsible for the **patellar reflex** (knee jerk reflex), which tests the integrity of the **L3-L4 nerve roots**. - It is innervated by the **femoral nerve** and is not involved in the **S1 reflex**.

Question 49: A 37-year-old obese woman presents to the neurology clinic complaining of severe pain in her left wrist and tingling sensation in her left thumb, index finger, and middle finger, and some part of her ring finger. The pain started as an occasional throb and she could ignore it or takes analgesics but now the pain is much worse and wakes her up at night. She is also concerned that these fingers are occasionally numb and sometimes tingle. She works as a typist and her pain mostly increases after typing all day. Her right wrist and fingers are fine. Nerve conduction studies reveal nerve compression. Which of the following additional clinical findings would most likely be present in this patient?

A. Inability to adduct the little finger
B. Paresthesia over the thenar eminence
C. Atrophied adductor pollicis muscle
D. Inability to oppose thumb to other digits (Correct Answer)
E. Flattened hypothenar eminence

Explanation: ***Inability to oppose thumb to other digits*** - The patient's symptoms (pain and tingling in the thumb, index, middle, and part of the ring finger, worse with typing, nocturnal worsening) are highly suggestive of **carpal tunnel syndrome**, which involves compression of the **median nerve**. - The median nerve innervates the **thenar muscles**, including the **opponens pollicis**, which is responsible for thumb opposition. Weakness or atrophy of this muscle can lead to an inability to oppose the thumb. *Inability to adduct the little finger* - The **adduction of the little finger** is primarily controlled by the **palmar interossei muscles** and the **abductor digiti minimi**, which are innervated by the **ulnar nerve**. - This symptom would suggest **ulnar nerve compression** or damage, which is not consistent with the patient's described sensory distribution in the hand. *Paresthesia over the thenar eminence* - The **thenar eminence** (the fleshy base of the thumb) receives its sensory innervation from the **palmar cutaneous branch of the median nerve**, which typically branches off *before* the carpal tunnel. - Therefore, in carpal tunnel syndrome, the sensation over the thenar eminence is usually preserved, making paresthesia in this area less likely. *Atrophied adductor pollicis muscle* - The **adductor pollicis muscle** is primarily innervated by the **ulnar nerve**. - Atrophy of this muscle would suggest **ulnar nerve pathology**, not median nerve compression as seen in carpal tunnel syndrome. *Flattened hypothenar eminence* - The **hypothenar eminence** (the fleshy mound at the base of the little finger) consists of muscles (abductor digiti minimi, flexor digiti minimi brevis, opponens digiti minimi) that are innervated by the **ulnar nerve**. - A flattened hypothenar eminence would indicate **ulnar nerve dysfunction**, not median nerve compression.

Question 50: A 24-year-old professional soccer player presents to the clinic with discomfort and pain while walking. He says that he has an unstable knee joint that started after an injury during a match last week. He adds that he heard a popping sound at the time of the injury. Physical examination of the knee reveals swelling of the knee joint with a positive anterior drawer test. Which of the following structures is most likely damaged in this patient?

A. Lateral collateral ligament
B. Ligamentum patellae
C. Anterior cruciate ligament (Correct Answer)
D. Medial collateral ligament
E. Posterior cruciate ligament

Explanation: ***Anterior cruciate ligament*** - The **"popping sound"** at the time of injury, associated with knee **instability** and a **positive anterior drawer test**, are classic signs of an **ACL tear**. - The **anterior drawer test** specifically assesses the integrity of the ACL by checking for excessive anterior translation of the tibia relative to the femur. *Lateral collateral ligament* - Injury to the LCL typically results from a **varus stress** to the knee and is less commonly associated with a distinct "popping" sound or significant instability. - While it causes pain and instability, the **anterior drawer test** would likely be negative, and a **varus stress test** would be more indicative. *Ligamentum patellae* - Damage to the patellar ligament usually presents as pain and difficulty with knee extension, often following a forceful quadriceps contraction. - It does not typically cause the described popping sensation or knee instability assessed by the anterior drawer test. *Medial collateral ligament* - MCL injuries commonly result from a **valgus stress** (force to the outside of the knee) and are diagnosed with a **valgus stress test**, not the anterior drawer test. - While it can cause instability, the "popping" sound and specific findings of the anterior drawer test point away from an isolated MCL injury. *Posterior cruciate ligament* - A PCL injury is often associated with a **posteriorly directed force** to the tibia, such as a dashboard injury, and would present with a **positive posterior drawer test**. - The clinical presentation of a **positive anterior drawer test** and significant anterior instability rules out isolated PCL damage.

Question 51: A 25-year-old man comes to the physician because of a 2-week history of numbness in his left lower extremity. One month ago, he sustained a fracture of the neck of the left fibula during soccer practice that was treated with immobilization in a plaster cast. Physical examination of the left lower extremity is most likely to show which of the following findings?

A. Loss of sensation over the medial calf
B. Impaired dorsiflexion of the foot (Correct Answer)
C. Loss of sensation on the sole of the foot
D. Inability to stand on tiptoes
E. Decreased ankle reflex

Explanation: ***Impaired dorsiflexion of the foot*** - A fracture of the **neck of the left fibula** can damage the **common fibular (peroneal) nerve**, which wraps around the fibular neck. - Damage to the common fibular nerve specifically affects its deep branch, leading to weakness of the **tibialis anterior muscle** and **impaired dorsiflexion** (foot drop). *Loss of sensation over the medial calf* - **Sensation over the medial calf** is supplied by the **saphenous nerve**, a branch of the femoral nerve, which is not typically injured with a fibular neck fracture. - Injury to the common fibular nerve primarily affects sensation over the **dorsum of the foot** and **lateral aspect of the leg**. *Loss of sensation on the sole of the foot* - **Sensation on the sole of the foot** is primarily mediated by the **tibial nerve** and its branches (medial and lateral plantar nerves). - Trauma to the fibular neck is unlikely to directly compromise the tibial nerve to this extent. *Inability to stand on tiptoes* - The **ability to stand on tiptoes** is controlled by the **gastrocnemius and soleus muscles**, which are innervated by the **tibial nerve**. - Injury to the common fibular nerve, rather than the tibial nerve, is associated with a fibular neck fracture. *Decreased ankle reflex* - The **ankle reflex** (Achilles reflex) is primarily mediated by the **S1 spinal nerve** via the **tibial nerve**. - While severe fibular nerve compression could potentially have some indirect effects, a decreased ankle reflex is not a primary or direct symptom of common fibular nerve palsy.

Question 52: A 32-year-old man comes to the emergency department because of a wound in his foot. Four days ago, he stepped on a nail while barefoot at the beach. Examination of the plantar surface of his right foot shows a purulent puncture wound at the base of his second toe with erythema and tenderness of the surrounding skin. The afferent lymphatic vessels from the site of the lesion drain directly into which of the following groups of regional lymph nodes?

A. Popliteal
B. Deep inguinal
C. Anterior tibial
D. Superficial inguinal (Correct Answer)
E. External iliac

Explanation: ***Superficial inguinal*** - Lymph from the **plantar surface of the foot** (including the base of the toes) drains into the **superficial inguinal lymph nodes**. - The **medial and central plantar surfaces** specifically follow the medial superficial lymphatic vessels that accompany the great saphenous vein system to reach these nodes. - These nodes are the **primary drainage site** and crucial in the initial immune response to infections of the lower limb. *Popliteal* - The **popliteal lymph nodes** primarily drain lymph from the **lateral foot and heel**, posterior leg, and knee. - They are located within the popliteal fossa and would not be the direct drainage site for a wound on the plantar surface of the second toe. *Deep inguinal* - **Deep inguinal lymph nodes** receive lymph from the superficial inguinal nodes, as well as from deeper structures of the thigh and glans penis/clitoris. - They are considered a **secondary drainage site** and not the primary destination for superficial foot infections. *Anterior tibial* - There are no well-defined major lymph nodes specifically termed "anterior tibial" that serve as a primary drainage site for the foot. - Lymphatics generally follow venous drainage patterns, and the anterior tibial vessels drain superiorly, not to a specific nodal group at this level. *External iliac* - **External iliac lymph nodes** receive lymph primarily from the deep inguinal nodes and pelvic organs. - They are a more **proximal group** in the lymphatic chain and not the direct initial drainage site for a foot infection.

Question 53: A 52-year-old man comes to the physician because of right shoulder pain that began after he repainted his house 1 week ago. Physical examination shows right subacromial tenderness. The pain is reproduced when the patient is asked to abduct the shoulder against resistance with the arm flexed forward by 30° and the thumb pointing downwards. The tendon of which of the following muscles is most likely to be injured in this patient?

A. Teres minor
B. Deltoid
C. Supraspinatus (Correct Answer)
D. Subscapularis
E. Infraspinatus

Explanation: ***Supraspinatus*** - The patient's presentation with **right shoulder pain** after painting (an overhead activity), subacromial tenderness, and pain reproduced by the described maneuver (the **"empty can" test**) is highly indicative of a **supraspinatus tendon injury**. - The supraspinatus is the most commonly injured rotator cuff muscle because its tendon passes through the **subacromial space**, making it vulnerable to impaction and degeneration. *Teres minor* - The teres minor is primarily involved in **external rotation** and adduction of the shoulder, not typically tested by the "empty can" maneuver. - Injury to the teres minor is less common than supraspinatus tears and usually presents with weakness in **external rotation**. *Deltoid* - The deltoid is a powerful muscle responsible for **shoulder abduction** (especially beyond the initial 15 degrees) and flexion, but it is less commonly involved in isolated tendonitis or tears from repetitive overhead activity. - Deltoid pain is usually diffuse and does not localize to the **subacromial space** in the same way as supraspinatus pathology. *Subscapularis* - The subscapularis is responsible for **internal rotation** and adduction of the shoulder. - Injuries typically present with weakness in internal rotation and may be tested with specific maneuvers like the **lift-off test** or **belly-press test**. *Infraspinatus* - The infraspinatus is a primary **external rotator** of the shoulder. - While it can be injured in conjunction with the supraspinatus or in isolation, its primary function is external rotation, and specific tests for it involve assessing resistance to **external rotation**.

Question 54: A 41-year-old woman comes to the doctor because of gradually progressive weakness in her right hand over the past few weeks. She goes to the gym to lift weights 5 times a week. With the dorsum of the right hand on a flat surface, the patient is unable to move her thumb to touch a pen held 2 cm above the interphalangeal joint of the thumb. An MRI of the right arm shows compression of a nerve that passes through the pronator teres muscle. Based on the examination findings, loss of innervation of which of the following muscles is most likely in this patient?

A. Opponens pollicis
B. First dorsal interosseus
C. Flexor pollicis longus
D. Adductor pollicis
E. Abductor pollicis brevis (Correct Answer)

Explanation: ***Abductor pollicis brevis*** - The patient's inability to move her thumb to touch a pen 2 cm above the interphalangeal joint, while the dorsum of the hand is flat, indicates a deficit in **thumb abduction**. The **abductor pollicis brevis** is the primary muscle responsible for this action and is innervated by the **median nerve**. - Compression of the **median nerve** at the **pronator teres** is consistent with an injury affecting the innervation of the abductor pollicis brevis, leading to the observed weakness. *Opponens pollicis* - The **opponens pollicis** is also innervated by the **median nerve** and is responsible for **thumb opposition** (bringing the thumb across the palm to touch other fingertips). - While opposition might be impaired in median nerve compression, the specific test described (lifting the thumb off a flat surface) directly assesses abduction, not opposition. *First dorsal interosseus* - The **first dorsal interosseus** muscle is responsible for **finger abduction**, specifically abducting the index finger away from the middle finger. It is innervated by the **ulnar nerve**. - The patient's symptoms are focused on the thumb and the median nerve distribution, making ulnar nerve involvement less likely. *Flexor pollicis longus* - The **flexor pollicis longus** muscle is responsible for **flexion of the interphalangeal joint of the thumb**. It is innervated by the **anterior interosseous nerve**, a branch of the median nerve. - While median nerve compression can affect this muscle, the described test specifically targets thumb abduction, not interphalangeal joint flexion. *Adductor pollicis* - The **adductor pollicis** muscle is responsible for **thumb adduction** (bringing the thumb towards the palm). It is innervated by the **ulnar nerve**. - The patient's symptom is one of weakness in lifting the thumb (abduction), not adduction, and points away from ulnar nerve pathology.

Question 55: A 26-year-old woman comes to the physician because of painful paresthesias in her foot. Examination shows decreased sensation in the first interdigital space and a hallux valgus deformity. This patient's paresthesias are most likely caused by compression of which of the following nerves?

A. Saphenous nerve
B. Sural nerve
C. Superficial peroneal nerve
D. Medial plantar nerve
E. Deep peroneal nerve (Correct Answer)

Explanation: ***Deep peroneal nerve*** - The **deep peroneal nerve** provides sensation to the **first interdigital space** of the foot, and its compression would explain the described paresthesias. - A **hallux valgus deformity** can alter foot mechanics and contribute to compression of this nerve. *Saphenous nerve* - The **saphenous nerve** provides sensory innervation to the **medial aspect of the lower leg and foot**, not specifically the interdigital spaces. - Its compression is typically associated with pain or paresthesias in the medial calf or ankle. *Sural nerve* - The **sural nerve** provides sensation to the **lateral aspect of the foot and ankle**. - Compression of this nerve would cause symptoms in a different distribution than described. *Superficial peroneal nerve* - The **superficial peroneal nerve** innervates the **dorsum of the foot**, excluding the first interdigital space and the area between the first and second toes. - Compression would typically result in sensory changes over the top of the foot. *Medial plantar nerve* - The **medial plantar nerve** provides sensation to the **medial two-thirds of the plantar foot** and the **first 3.5 toes** on the plantar surface, not the dorsal interdigital space. - Compression is often associated with symptoms similar to tarsal tunnel syndrome.

Question 56: A newborn infant is born at 41 weeks gestation to a healthy G1P0 mother. The delivery was complicated by shoulder dystocia. The infant is in the 89th and 92nd percentiles for height and weight, respectively. The mother's past medical history is notable for diabetes mellitus and obesity. Immediately after birth, the child's temperature is 99°F (37.2°C), blood pressure is 90/50 mmHg, pulse is 120/min, and respirations are 24/min. The child demonstrates a strong cry and pink upper and lower extremities bilaterally. The left arm is adducted and internally rotated at the shoulder and extended at the elbow. Extension at the elbow and flexion and extension of the wrist appear to be intact in the left upper extremity. The right upper extremity appears to have normal strength and range of motion in all planes. Which of the following sets of nerves or nerve roots is most likely affected in this patient?

A. Axillary nerve only
B. Suprascapular nerve only
C. C5 and C6 nerve roots (Correct Answer)
D. C5, C6, and C7 nerve roots
E. Musculocutaneous nerve only

Explanation: ***C5 and C6 nerve roots*** - The presentation of a newborn with an adducted and internally rotated shoulder, and an extended elbow, is characteristic of **Erb's palsy**, which results from injury to the **upper brachial plexus** (C5-C6 nerve roots). This classic "waiter's tip" position affects muscles innervated by these roots, including the **deltoid**, **supraspinatus**, **infraspinatus**, and **biceps brachii**. - **Shoulder dystocia** during a complicated delivery is a common cause of Erb's palsy due to excessive lateral traction on the neck, stretching the upper brachial plexus. *Axillary nerve only* - Injury to the **axillary nerve** primarily affects **shoulder abduction** (deltoid) and sensation over the lateral shoulder. While abduction is compromised in Erb's palsy, other impairments like **elbow flexion** weakness indicate more widespread nerve involvement than just the axillary nerve. - The axillary nerve is a terminal branch of the posterior cord, which is formed by the posterior divisions of the upper, middle, and lower trunks of the brachial plexus. *Suprascapular nerve only* - The **suprascapular nerve** innervates the **supraspinatus** and **infraspinatus muscles**, responsible for the initial 15 degrees of shoulder abduction and external rotation, respectively. While these movements are affected in Erb's palsy, the presentation also includes **elbow extension** (due to biceps weakness), indicating involvement beyond just the suprascapular nerve. - This nerve originates directly from the **upper trunk** of the brachial plexus (C5-C6). *C5, C6, and C7 nerve roots* - Involvement of the **C7 nerve root** would typically lead to additional weakness in the **wrist extensors** and **finger extensors**, which are noted as intact in the left upper extremity. - This more extensive injury would suggest a **total brachial plexus palsy** or a more severe form of Erb's palsy that extends into the middle trunk, which is not fully supported by the intact wrist and finger movements. *Musculocutaneous nerve only* - The **musculocutaneous nerve** primarily innervates the **biceps brachii**, **brachialis**, and **coracobrachialis muscles**, responsible for **elbow flexion**. While elbow flexion is impaired in this case, the additional **shoulder adduction** and **internal rotation** dysfunction, due to weakness in the deltoid and rotator cuff, points to a broader injury involving the C5-C6 nerve roots rather than an isolated musculocutaneous nerve lesion. - This nerve is a terminal branch of the lateral cord, formed by the anterior divisions of the upper and middle trunks (C5-C7).

Question 57: A 23-year-old college student was playing basketball when he fell directly onto his left elbow. He had sudden, intense pain and was unable to move his elbow. He was taken immediately to the emergency room by his teammates. He has no prior history of trauma or any chronic medical conditions. His blood pressure is 128/84 mm Hg, the heart rate is 92/min, and the respiratory rate is 14/min. He is in moderate distress and is holding onto his left elbow. On physical examination, pinprick sensation is absent in the left 5th digit and the medial aspect of the left 4th digit. Which of the following is the most likely etiology of this patient’s condition?

A. Axillary neuropathy
B. Median neuropathy
C. Radial neuropathy
D. Musculocutaneous neuropathy
E. Ulnar neuropathy (Correct Answer)

Explanation: ***Ulnar neuropathy*** - Direct trauma to the elbow, combined with **pinprick sensation loss** in the **5th digit** and the **medial aspect of the 4th digit**, is highly indicative of **ulnar nerve injury**. - The ulnar nerve passes through the **cubital tunnel** at the elbow, making it vulnerable to compression or trauma from direct falls. *Axillary neuropathy* - An **axillary nerve injury** typically presents with weakness in **shoulder abduction** (deltoid muscle) and sensory loss over the **lateral aspect of the shoulder**. - This clinical picture does not match the patient's sensory deficits in the fingers. *Median neuropathy* - **Median nerve injury** at the elbow would typically cause sensory loss in the **first three fingers and the lateral half of the fourth finger**, along with **weakness in thumb opposition** and **flexion of the index and middle fingers**. - The sensory loss described in the patient does not align with median nerve distribution. *Radial neuropathy* - **Radial nerve injury** at the elbow level would primarily result in **wrist drop** and sensory loss over the **dorsal aspect of the hand**, particularly the **first three and a half digits**. - These are not the clinical findings presented by the patient. *Musculocutaneous neuropathy* - **Musculocutaneous nerve injury** would cause weakness in **elbow flexion** (biceps and brachialis muscles) and sensory loss over the **lateral forearm**. - The patient's reported sensory loss is in a different distribution and no specific motor deficits of elbow flexion are mentioned.

Question 58: A newborn infant is born at 42 weeks gestation to a healthy 36-year-old G1P0. The delivery was complicated by prolonged labor and shoulder dystocia. The child is in the 87th and 91st percentiles for height and weight at birth, respectively. The mother’s past medical history is notable for diabetes mellitus and obesity. Immediately after birth, the child’s temperature is 99°F (37.2°C), blood pressure is 90/50 mmHg, pulse is 120/min, and respirations are 24/min. The child demonstrates a strong cry and pink upper and lower extremities bilaterally. The right arm is adducted and internally rotated at the shoulder and extended at the elbow. Flexion and extension of the wrist and digits appear to be intact in the right upper extremity. Which of the following muscles would most likely have normal strength in this patient?

A. Brachialis
B. Teres minor
C. Brachioradialis
D. Triceps (Correct Answer)
E. Biceps

Explanation: ***Triceps*** - This clinical presentation is consistent with an **Erb-Duchenne palsy (Erb's palsy)**, which typically involves injury to the **upper brachial plexus roots (C5-C6)**. - The **triceps muscle**, innervated primarily by the **radial nerve (C6-C8)**, often maintains normal strength in Erb's palsy because its C7 and C8 innervation is usually spared. *Brachialis* - The **brachialis muscle**, a primary elbow flexor, is innervated by the **musculocutaneous nerve (C5-C6)**, making it highly susceptible to injury in Erb's palsy. - Weakness or paralysis of the brachialis contributes to the characteristic **extended elbow** posture. *Teres minor* - The **teres minor muscle**, responsible for external rotation and stabilization of the shoulder, is innervated by the **axillary nerve (C5-C6)**. - Damage to these roots in Erb's palsy would likely impair teres minor function, contributing to the **internal rotation** of the shoulder seen in the presentation. *Brachioradialis* - The **brachioradialis muscle** is another elbow flexor, innervated by the **radial nerve (C5-C6)**, and therefore would likely be affected in Erb's palsy. - Its involvement would contribute to weakness in elbow flexion, especially with the forearm in a neutral position. *Biceps* - The **biceps muscle**, another key elbow flexor and supinator, is innervated by the **musculocutaneous nerve (C5-C6)**. - Injury to these roots would directly impair biceps function, leading to significant weakness in elbow flexion and contributing to the **adducted and internally rotated shoulder** with an extended elbow presentation.

Question 59: A 31-year-old woman presents with difficulty walking and climbing stairs for the last 3 weeks. She has no history of trauma. The physical examination reveals a waddling gait with the trunk swaying from side-to-side towards the weight-bearing limb. When she stands on her right leg, the pelvis on the left side falls. When she stands on her left leg, the pelvis remains level. Which of the following nerves is most likely injured in this patient?

A. Right inferior gluteal nerve
B. Right obturator nerve
C. Right superior gluteal nerve (Correct Answer)
D. Right femoral nerve
E. Left femoral nerve

Explanation: ***Right superior gluteal nerve*** - The presentation of a **waddling gait** and the **Trendelenburg sign** (pelvis dropping on the unsupported side) is characteristic of **gluteus medius** and **minimus** weakness. - These muscles are innervated by the **superior gluteal nerve**. In this case, when the patient stands on her right leg, the left pelvis falls, indicating weakness of the right gluteus medius/minimus. *Right inferior gluteal nerve* - The **inferior gluteal nerve** innervates the **gluteus maximus**, which is primarily responsible for hip extension. - Damage to this nerve would primarily lead to difficulty with **climbing stairs** and rising from a seated position, but not typically the specific pelvic drop described. *Right obturator nerve* - The **obturator nerve** innervates the **adductor muscles** of the thigh. - Damage would result in weakness of hip adduction and **medial thigh sensory deficits**, which are not the primary symptoms here. *Right femoral nerve* - The **femoral nerve** innervates the **quadriceps femoris** and the **sartorius**, responsible for knee extension and hip flexion. - Injury would cause difficulty with **knee extension** and **hip flexion**, potentially leading to knee buckling or instability, which is not consistent with the Trendelenburg sign observed. *Left femoral nerve* - Injury to the left femoral nerve would affect the **left quadriceps** and **sartorius** muscles. - This would cause weakness in extending the left knee and flexing the left hip, which is not consistent with the observed **right-sided gluteal weakness** indicated by the Trendelenburg sign on the right.

Question 60: A 65-year-old man comes to a follow-up appointment with his surgeon 2 months after undergoing hip replacement surgery. His major concern at this visit is that he is still limping since the surgery even after the post-operative pain has subsided. Specifically, when he stands on his right leg, he feels that he has to lean further to the right in order to maintain balance. When standing on his left leg, he feels that he is able to step normally. Damage to which of the following nerves would most likely present with this patient's symptoms?

A. Common peroneal nerve
B. Tibial nerve
C. Femoral nerve
D. Inferior gluteal nerve
E. Superior gluteal nerve (Correct Answer)

Explanation: ***Superior gluteal nerve*** - The superior gluteal nerve innervates the **gluteus medius** and minimus muscles, which are crucial for **hip abduction** and stabilizing the pelvis during gait. - Damage to this nerve or its muscles on one side (e.g., right side) would lead to a **Trendelenburg gait**, where the pelvis drops on the unaffected side when standing on the affected leg, and the patient compensates by leaning towards the affected side. *Common peroneal nerve* - The common peroneal nerve primarily innervates muscles responsible for **dorsiflexion** and **eversion of the foot**. - Damage to this nerve commonly results in **foot drop** and an inability to evert the foot, which is not the primary symptom described. *Tibial nerve* - The tibial nerve innervates muscles responsible for **plantarflexion** and **inversion of the foot**, as well as the intrinsic muscles of the sole. - Injury typically presents with difficulty walking on tiptoes, toe curling, and sensory loss in the sole of the foot, not pelvic instability. *Femoral nerve* - The femoral nerve innervates the **quadriceps femoris** and sartorius muscles, - Damage leads to weakness in **knee extension** and loss of sensation over the anterior thigh and medial leg. *Inferior gluteal nerve* - The inferior gluteal nerve innervates the **gluteus maximus** muscle, which is essential for **hip extension** and external rotation. - Damage would primarily affect activities like climbing stairs or standing up from a seated position, rather than the specific lateral pelvic instability described.

Question 61: A 38-year-old man comes to the physician because of a 3-week history of right-sided knee pain. He works as a bricklayer and reports that the pain worsens when he kneels. He has no history of trauma. Examination of the right knee shows erythema, fluctuant swelling, and tenderness on palpation of the kneecap. Passive flexion of the right knee elicits pain. Which of the following structures is most likely affected in this patient?

A. Prepatellar bursa (Correct Answer)
B. Synovial membrane
C. Medial meniscus
D. Anserine bursa
E. Suprapatellar bursa

Explanation: ***Prepatellar bursa*** - The patient's profession as a **bricklayer** and the associated pain when **kneeling** strongly suggest inflammation of the prepatellar bursa, often called "housemaid's knee." - **Erythema**, **fluctuant swelling**, and **tenderness** directly over the kneecap (patella) are classic signs of prepatellar bursitis. *Synovial membrane* - Inflammation of the synovial membrane (**synovitis**) typically presents with more diffuse joint swelling, stiffness, and pain with active and passive range of motion. - While it can cause pain, the localized, fluctuant swelling directly over the kneecap is less characteristic of primary synovitis. *Medial meniscus* - A **meniscal injury** would typically cause localized pain along the joint line, clicking or locking sensations, and pain with specific twisting or squatting movements. - It would not typically present with the described erythema and fluctuant swelling directly over the patella. *Anserine bursa* - The anserine bursa is located on the **medial side of the knee**, about 2-3 inches below the joint line, where the sartorius, gracilis, and semitendinosus tendons insert. - Inflammation here would cause pain and tenderness along the medial aspect of the knee rather than directly over the kneecap. *Suprapatellar bursa* - The suprapatellar bursa is located **above the patella**, deep to the quadriceps tendon. - While it can swell, its inflammation is usually associated with intra-articular conditions or direct trauma to the quadriceps tendon area, and not typically from occupational kneeling that directly irritates the patella itself.

Question 62: A 23-year-old female college basketball player presents in Sports Clinic after she felt a "pop" in her knee after coming down with a rebound. To examine the patient, you have her lie down on the table with her knees flexed 90 degrees. With your hand around her knee you are able to draw the tibia toward you from underneath the femur. The torn structure implicated by this physical exam maneuver has which of the following attachments?

A. The posterior intercondylar area of tibia and the posteromedial aspect of the lateral femur
B. The anterior intercondylar area of tibia and the posteromedial aspect of the lateral femur (Correct Answer)
C. The patella and tibial tuberosity
D. The lateral epicondyle of the femur and the head of fibula
E. The medial condyle of the femur and the medial condyle of the tibia

Explanation: ***The anterior intercondylar area of tibia and the posteromedial aspect of the lateral femur*** - The patient's presentation with a "pop" in the knee after a basketball maneuver and a positive **anterior drawer test** (drawing the tibia forward) is classic for an **anterior cruciate ligament (ACL) tear**. - The **ACL originates from the anterior intercondylar area of the tibia** and **inserts into the posteromedial aspect of the lateral femoral condyle**. *The posterior intercondylar area of tibia and the posteromedial aspect of the lateral femur* - This describes the attachments of the **posterior cruciate ligament (PCL)**. - A PCL tear would typically be indicated by a **posterior drawer test** (pushing the tibia backward), which is not described. *The patella and tibial tuberosity* - These are the attachment points for the **patellar ligament** (or patellar tendon). - Injury to the patellar ligament would cause pain and difficulty with knee extension, but not primarily instability evident with an anterior drawer test. *The lateral epicondyle of the femur and the head of fibula* - These are the attachment points for the **fibular collateral ligament (LCL)**. - An LCL injury would present with pain on the lateral side of the knee and instability to **varus stress**, not an anterior drawer. *The medial condyle of the femur and the medial condyle of the tibia* - These are general areas involved with the **medial collateral ligament (MCL)**. - An MCL injury would cause pain on the medial side of the knee and instability to **valgus stress**, not an anterior drawer.

Question 63: A 68-year-old right hand-dominant man presents to the emergency room complaining of severe right arm pain after falling down a flight of stairs. He landed on his shoulder and developed immediate severe upper arm pain. Physical examination reveals a 2-cm laceration in the patient’s anterior right upper arm. Bone is visible through the laceration. An arm radiograph demonstrates a displaced comminuted fracture of the surgical neck of the humerus. Irrigation and debridement is performed immediately and the patient is scheduled to undergo definitive operative management of his fracture. In the operating room on the following day, the operation is more complicated than expected and the surgeon accidentally nicks a neurovascular structure piercing the coracobrachialis muscle. This patient would most likely develop a defect in which of the following?

A. Wrist extension
B. Medial arm skin sensation
C. Forearm pronation
D. Elbow extension
E. Lateral forearm skin sensation (Correct Answer)

Explanation: ***Lateral forearm skin sensation*** - The description of nicking a neurovascular structure piercing the **coracobrachialis muscle** points to injury of the **musculocutaneous nerve**. - The **musculocutaneous nerve** innervates the **lateral forearm skin** via its terminal branch, the lateral cutaneous nerve of the forearm (also known as the lateral antebrachial cutaneous nerve). *Wrist extension* - **Wrist extension** is primarily mediated by muscles innervated by the **radial nerve**. - Injury to the musculocutaneous nerve would not directly affect wrist extension. *Medial arm skin sensation* - **Medial arm skin sensation** is primarily supplied by the **medial brachial cutaneous nerve**. - This nerve is distinct from the musculocutaneous nerve, which supplies the lateral forearm. *Forearm pronation* - **Forearm pronation** is controlled by the **pronator teres** and **pronator quadratus muscles**, which are innervated by the **median nerve**. - The musculocutaneous nerve primarily innervates the biceps brachii, brachialis, and coracobrachialis, which are involved in elbow flexion. *Elbow extension* - **Elbow extension** is performed by the **triceps brachii muscle**, which is innervated by the **radial nerve**. - The musculocutaneous nerve's primary motor function is elbow flexion.

Question 64: A 13-year-old girl is brought to the physician by her father because of a 1-month history of pain in her right knee. She is a competitive volleyball player and has missed several games recently due to pain. Examination shows swelling distal to the right knee joint on the anterior surface of the proximal tibia; there is no overlying warmth or deformity. Extension of the right knee against resistance is painful. Which of the following structures is attached to the affected anterior tibial area?

A. Patellar ligament (Correct Answer)
B. Iliotibial band
C. Pes anserinus tendon
D. Quadriceps tendon
E. Anterior cruciate ligament

Explanation: ***Patellar ligament*** - The symptoms described, particularly **pain in the right knee worse with activity** in a young, active individual with **swelling distal to the knee joint on the anterior surface of the proximal tibia**, are classic for **Osgood-Schlatter disease**. - This condition involves inflammation of the **patellar ligament** (also known as the patellar tendon) insertion onto the **tibial tuberosity**, which is the bony prominence on the anterior proximal tibia. *Iliotibial band* - The **iliotibial band (IT band)** runs along the lateral aspect of the thigh and inserts on the **lateral condyle of the tibia (Gerdy's tubercle)**, not the anterior proximal tibia. - **IT band syndrome** typically causes lateral knee pain, often seen in runners, and not central anterior tibial swelling. *Pes anserinus tendon* - The **pes anserinus tendon** is formed by the conjoined tendons of the **sartorius**, **gracilis**, and **semitendinosus muscles**, inserting on the **medial proximal tibia**. - Inflammation here (**pes anserinus bursitis/tendinitis**) would cause pain and swelling on the medial side of the knee, not the anterior aspect. *Quadriceps tendon* - The **quadriceps tendon** connects the quadriceps muscles to the **superior pole of the patella**, not the anterior proximal tibia. - Conditions affecting this tendon typically cause pain above or at the patella, not distal to the knee joint. *Anterior cruciate ligament* - The **anterior cruciate ligament (ACL)** is an intra-articular ligament that connects the **femur to the tibia within the knee joint**. - An **ACL injury** typically presents with acute pain, instability, and a "popping" sensation, not chronic swelling on the anterior aspect of the proximal tibia.

Question 65: A 37-year-old man is brought to the emergency department after being attacked with a knife. Physical examination shows a 4-cm laceration in the midline of the right forearm. An MRI of the right arm shows damage to a nerve that runs between the superficial and deep flexor digitorum muscles. Loss of sensation over which of the following areas is most likely in this patient?

A. Medial aspect of the forearm
B. Fingertip of the index finger (Correct Answer)
C. Dorsum of the thumb
D. Palmar surface of the little finger
E. Lateral aspect of the forearm

Explanation: ***Fingertip of the index finger*** - The nerve running between the superficial and deep **flexor digitorum muscles** in the forearm is the **median nerve**. - The median nerve supplies sensation to the **palmar aspect of the thumb, index, middle, and radial half of the ring finger**, including their fingertips. *Medial aspect of the forearm* - Sensation to the medial aspect of the forearm is primarily supplied by the **medial antebrachial cutaneous nerve**, a branch of the brachial plexus. - This nerve is located superficially and is not typically associated with the deep flexor muscles. *Dorsum of the thumb* - The dorsum of the thumb is primarily innervated by the **radial nerve** and its superficial branch. - The median nerve's sensory distribution does not extend to the dorsum of the thumb. *Palmar surface of the little finger* - Sensation to the palmar surface of the little finger is supplied by the **ulnar nerve**. - The ulnar nerve runs medial to the median nerve and innervates the ulnar side of the hand. *Lateral aspect of the forearm* - Sensation to the lateral aspect of the forearm is mainly supplied by the **lateral antebrachial cutaneous nerve**, which is a continuation of the musculocutaneous nerve. - This area is generally not affected by median nerve injuries in the forearm.

Question 66: A 3629-g (8-lb) newborn is examined shortly after spontaneous vaginal delivery. She was delivered at 40 weeks' gestation and pregnancy was uncomplicated. Her mother is concerned because she is not moving her left arm as much as her right arm. Physical examination shows her left arm to be adducted and internally rotated, with the forearm extended and pronated, and the wrist flexed. The Moro reflex is present on the right side but absent on the left side. Which of the following brachial plexus structures is most likely injured in this infant?

A. Upper trunk (Correct Answer)
B. Axillary nerve
C. Lower trunk
D. Long thoracic nerve
E. Posterior cord

Explanation: ***Upper trunk*** - The symptoms described, including the arm being **adducted, internally rotated**, with the forearm extended and pronated, and a **flexed wrist**, are characteristic of **Erb-Duchenne palsy**, an injury to the **upper trunk** of the brachial plexus (C5-C6 nerve roots). - The absence of the **Moro reflex** on the affected side further indicates an injury to the **upper brachial plexus**, as these roots contribute to the reflex arc. *Axillary nerve* - An injury to the **axillary nerve** would primarily affect the **deltoid** and **teres minor muscles**, leading to weakness in **shoulder abduction** and external rotation. - While shoulder abduction is impaired in this case, the more widespread deficits affecting multiple arm movements point to a more proximal brachial plexus injury rather than an isolated axillary nerve lesion. *Lower trunk* - Injury to the **lower trunk** (C8-T1 nerve roots) typically results in **Klumpke's palsy**, characterized by weakness or paralysis of the **intrinsic hand muscles** and **flexors of the wrist and fingers**, leading to a "claw hand" deformity. - The described presentation does not align with the classic features of Klumpke's palsy. *Long thoracic nerve* - An injury to the **long thoracic nerve** would cause **paralysis of the serratus anterior muscle**, leading to **scapular winging** (the medial border of the scapula protruding posteriorly, especially when pushing against a wall). - This symptom is not described in the patient's presentation. *Posterior cord* - The **posterior cord** gives rise to the axillary and radial nerves. Injury to the posterior cord would affect muscles innervated by these nerves, including the **deltoid, triceps**, and **extensors of the wrist and fingers**. - While some of these movements (e.g., forearm extension) are affected, the specific "waiter's tip" posture strongly points to an upper trunk injury, which involves a broader distribution of muscles than just those supplied by the posterior cord.

Question 67: An 18-year-old man comes to the physician because of severe left shoulder pain after a basketball match. During the game, the patient sustained an injury to the posterior part of his outstretched arm after being blocked by a defender. Examination shows no gross deformity of the left shoulder. Palpation of the shoulder elicits mild tenderness. Internal rotation of the arm against resistance shows weakness. These findings are most specific for injury to which of the following muscles?

A. Infraspinatus
B. Deltoid
C. Supraspinatus
D. Teres minor
E. Subscapularis (Correct Answer)

Explanation: ***Subscapularis*** - The **subscapularis** is the primary muscle responsible for **internal rotation** of the arm. Weakness in this movement against resistance is a key indicator of its injury. - Injury can occur with a **sudden force** applied to an **outstretched arm**, especially with a posterior impact, as this can force the humerus into excessive external rotation and anterior translation, tearing the subscapularis. *Infraspinatus* - The **infraspinatus** is primarily involved in **external rotation** of the arm; its injury would lead to weakness in external rotation, not internal rotation. - It also assists in **shoulder abduction**, but its main isolated action is external rotation. *Deltoid* - The **deltoid** muscle is the main abductor of the arm and also assists in **flexion and extension**, depending on which fibers are active. - Injury to the deltoid would typically result in weakness with **arm abduction** and possibly a visible deformity, which is not noted here. *Supraspinatus* - The **supraspinatus** is primarily responsible for the **initiation of arm abduction** (first 15-20 degrees) and stabilizing the humeral head. - While it is a common rotator cuff injury, its damage would manifest as pain and weakness during abduction, not internal rotation. *Teres minor* - The **teres minor** is another muscle involved in **external rotation** of the arm and also helps to stabilize the shoulder joint. - Its injury would present with weakness in external rotation, similar to the infraspinatus, and not internal rotation.

Question 68: A 44-year-old woman comes to the physician for the evaluation of right knee pain for 1 week. The pain began after the patient twisted her knee during basketball practice. At the time of the injury, she felt a popping sensation and her knee became swollen over the next few hours. The pain is exacerbated by walking up or down stairs and worsens throughout the day. She also reports occasional locking of the knee. She has been taking acetaminophen during the past week, but the pain is worse today. Her mother has rheumatoid arthritis. The patient is 155 cm (4 ft 11 in) tall and weighs 75 kg (165 lb); BMI is 33 kg/m2. Vital signs are within normal limits. Examination shows effusion of the right knee; range of motion is limited by pain. There is medial joint line tenderness. Knee extension with rotation results in an audible snap. Further evaluation is most likely to show which of the following?

A. Hyperintense line in the meniscus on MRI (Correct Answer)
B. Trabecular loss in the proximal femur on x-ray
C. Posterior tibial translation on examination
D. Erosions and synovial hyperplasia on MRI
E. Anterior tibial translation on examination

Explanation: ***Hyperintense line in the meniscus on MRI*** - This patient's symptoms of a **popping sensation**, rapid swelling, pain with stairs, and **locking of the knee** after a twisting injury are highly suggestive of a **meniscal tear**. - An MRI with a **hyperintense line within the substance of the meniscus extending to the articular surface** is the classic finding for a meniscal tear. *Trabecular loss in the proximal femur on x-ray* - **Trabecular loss** in the proximal femur on X-ray is characteristic of **osteoporosis**, a condition affecting bone density. - While this patient is a woman, there are no other clinical signs pointing to osteoporosis, and it would not explain the acute knee injury symptoms. *Posterior tibial translation on examination* - **Posterior tibial translation** on examination (positive posterior drawer test) indicates damage to the **posterior cruciate ligament (PCL)**. - While a knee injury, the symptoms of initial popping, rapid swelling, and locking are more characteristic of a meniscal tear or ACL injury than an isolated PCL tear. *Erosions and synovial hyperplasia on MRI* - **Erosions and synovial hyperplasia** on MRI are classic findings in **inflammatory arthropathies** like **rheumatoid arthritis**, which primarily affect the joint lining (synovium). - Although the patient's mother has rheumatoid arthritis, there is no indication of chronic inflammatory arthritis, and the patient's acute injury symptoms are not consistent with this. *Anterior tibial translation on examination* - **Anterior tibial translation** on examination (positive anterior drawer test or Lachman test) indicates damage to the **anterior cruciate ligament (ACL)**. - While an ACL injury can cause a pop and swelling, the prominent symptom of **locking** is more specifically associated with meniscal tears where a torn piece of cartilage intermittently blocks joint movement.

Question 69: A 72-year-old woman presents with left lower limb swelling. She first noticed her left leg was swollen about 2 weeks ago. She denies any pain and initially thought the swelling would subside on its own. Past medical history is significant for hypertension and hyperlipidemia. She is a smoker with a 35 pack-year history and an occasional drinker. She takes chlorthalidone, lisinopril, atorvastatin and a multivitamin. On physical examination, her left leg appears larger than her right with 2+ pitting edema up to her knee. She also has a few distended superficial veins along the posterior aspect of her left leg. Lower extremities have 2+ pulses bilaterally. The ultrasound of her left lower thigh and leg shows an obstructing thrombosis of the distal portion of the femoral vein. Which of the following veins serve as collateral pathways to help mitigate the consequences of this patient's condition?

A. Giacomini vein
B. Fibular vein
C. Accessory saphenous vein
D. Perforator veins (Correct Answer)
E. Deep femoral vein

Explanation: ***Perforator veins*** - **Perforator veins** connect the **superficial venous system** to the **deep venous system**, normally allowing blood to flow from superficial to deep veins through one-way valves. - In cases of **deep vein thrombosis (DVT)**, when the deep venous system is obstructed, these veins can serve as **important collateral pathways**, allowing blood to be rerouted from the obstructed deep system to the superficial system, thereby preventing excessive venous engorgement and helping to reduce severe edema. - This explains the **distended superficial veins** seen on examination in this patient—blood is being diverted through perforators to the superficial system. *Giacomini vein* - The **Giacomini vein** is a **superficial vein** connecting the small saphenous vein to the great saphenous vein, typically in the popliteal fossa and posterior thigh. - It primarily shunts blood within the **superficial system** and does not provide significant collateral drainage when the deep venous system is occluded. *Fibular vein* - The **fibular vein** (also known as the peroneal vein) is a **deep vein** of the lower leg, running alongside the fibula and draining into the posterior tibial veins. - While it is part of the deep venous system, the thrombosis in this case is in the **femoral vein** (more proximal), so the fibular vein would drain into the same obstructed system rather than serving as a bypass collateral. *Accessory saphenous vein* - The **accessory saphenous vein** is a **superficial vein** that runs parallel to and is a tributary of the great saphenous vein in the thigh. - It is part of the superficial system and does not provide a collateral pathway **from** the obstructed deep system, though it may carry increased flow if perforators are diverting blood to the superficial system. *Deep femoral vein* - The **deep femoral vein** (profunda femoris vein) is a **deep vein** that drains the deep compartments of the thigh and joins the common femoral vein. - While it can provide some collateral drainage when the superficial femoral vein (femoral vein) is occluded, it ultimately drains into the **same deep venous system** proximally and is not the primary collateral mechanism connecting superficial and deep systems.

Question 70: A 61-year-old woman comes to the physician for a follow-up examination 1 week after undergoing right-sided radical mastectomy and axillary lymph node dissection for breast cancer. She says that she has been unable to comb her hair with her right hand since the surgery. Physical examination shows shoulder asymmetry. She is unable to abduct her right arm above 90 degrees. When she pushes against a wall, there is protrusion of the medial aspect of the right scapula. Injury to which of the following nerves is the most likely cause of this patient's condition?

A. Long thoracic nerve (Correct Answer)
B. Thoracodorsal nerve
C. Axillary nerve
D. Suprascapular nerve
E. Upper trunk of the brachial plexus

Explanation: ***Long thoracic nerve*** - Injury to the **long thoracic nerve** leads to paralysis of the **serratus anterior muscle**, causing **scapular winging** (protrusion of the medial scapula) especially when pushing against a wall. - The serratus anterior is crucial for **scapular protraction** and stabilizing the scapula during **abduction of the arm above 90 degrees**, explaining her inability to comb her hair. *Thoracodorsal nerve* - The **thoracodorsal nerve** innervates the **latissimus dorsi muscle**, which is responsible for **adduction**, extension, and internal rotation of the arm. - Injury to this nerve would primarily affect these movements, not shoulder abduction above 90 degrees or scapular winging. *Axillary nerve* - The **axillary nerve** innervates the **deltoid muscle** and **teres minor**. - Damage would primarily result in impaired **arm abduction up to 90 degrees** and loss of sensation over the lateral shoulder, but not scapular winging. *Suprascapular nerve* - The **suprascapular nerve** supplies the **supraspinatus** and **infraspinatus muscles**, which are involved in the initiation of arm abduction and external rotation, respectively. - Injury would cause weakness in these movements and shoulder pain, but not scapular winging. *Upper trunk of the brachial plexus* - Injury to the **upper trunk of the brachial plexus** (C5-C6) affects several nerves and muscles, leading to conditions like **Erb's palsy**. - While it can impair shoulder function and abduction, the specific finding of scapular winging points more directly to long thoracic nerve damage rather than a generalized upper trunk injury, as the long thoracic nerve (C5-C7) is often spared in classic Erb's palsy.

Question 71: A 19-year-old collegiate football player sustains an injury to his left knee during a game. He was running with the ball when he dodged a defensive player and fell, twisting his left knee. He felt a “pop” as he fell. When he attempts to bear weight on his left knee, it feels unstable, and "gives way." He needs assistance to walk off the field. The pain is localized diffusely over the knee and is non-radiating. His past medical history is notable for asthma. He uses an albuterol inhaler as needed. He does not smoke or drink alcohol. On exam, he has a notable suprapatellar effusion. Range of motion is limited in the extremes of flexion. When the proximal tibia is pulled anteriorly while the knee is flexed and the patient is supine, there is 1.5 centimeter of anterior translation. The contralateral knee translates 0.5 centimeters with a similar force. The injured structure in this patient originates on which of the following bony landmarks?

A. Posteromedial aspect of the lateral femoral condyle (Correct Answer)
B. Lateral aspect of the lateral femoral condyle
C. Lateral aspect of the medial femoral condyle
D. Tibial tubercle
E. Medial aspect of the medial femoral condyle

Explanation: ***Posteromedial aspect of the lateral femoral condyle*** - The patient's presentation of a **\"pop\"**, knee instability, and a **positive anterior drawer test** (excessive anterior translation of the tibia) strongly indicates an **anterior cruciate ligament (ACL) tear**. - The **ACL originates** from the **posteromedial aspect of the lateral femoral condyle** and inserts onto the anterior intercondylar area of the tibia. *Lateral aspect of the lateral femoral condyle* - This area is typically associated with the origin of the **lateral collateral ligament (LCL)**, which would present with instability to **varus stress**, not anterior translation. - Injuries to the LCL do not typically cause the described \"giving way\" sensation in the same manner as an ACL tear. *Lateral aspect of the medial femoral condyle* - The medial femoral condyle is primarily associated with the origin of the **medial collateral ligament (MCL)**. - An MCL injury would typically present with **valgus instability** and pain on the medial side of the knee. *Tibial tubercle* - The tibial tubercle is the insertion point for the **patellar tendon**, which is the distal attachment of the quadriceps femoris muscle. - Injuries here are more commonly associated with conditions like **Osgood-Schlatter disease** in adolescents or patellar tendon ruptures, not typically ACL-like instability. *Medial aspect of the medial femoral condyle* - This region is the primary origin for the **medial collateral ligament (MCL)**. - MCL tears are often caused by **valgus stress** and would result in increased laxity to valgus forces, not anterior tibial translation.

Question 72: A 45-year-old male presents to his primary care provider with an abnormal gait. He was hospitalized one week prior for acute cholecystitis and underwent a laparoscopic cholecystectomy. He received post-operative antibiotics via intramuscular injection. He recovered well and he was discharged on post-operative day #3. However, since he started walking after the operation, he noticed a limp that has not improved. On exam, his left hip drops every time he raises his left foot to take a step. In which of the following locations did this patient likely receive the intramuscular injection?

A. Superomedial quadrant of the buttock (Correct Answer)
B. Superolateral quadrant of the buttock
C. Anteromedial thigh
D. Inferomedial quadrant of the buttock
E. Inferolateral quadrant of the buttock

Explanation: ***Superomedial quadrant of the buttock*** - An injection in the **superomedial quadrant of the buttock** is the most common site for iatrogenic injury to the **superior gluteal nerve**. - The superior gluteal nerve exits the pelvis through the greater sciatic foramen above the piriformis muscle and runs in the **superomedial** region of the buttock. - Injury to the superior gluteal nerve results in weakness of the **gluteus medius and minimus muscles**, leading to a **Trendelenburg gait** (hip drops on the contralateral side when lifting that leg), which is consistent with the patient's symptoms. - This is why the **superolateral quadrant** is recommended for safe IM injections. *Superolateral quadrant of the buttock* - The **superolateral quadrant** is the **safest site** for intramuscular gluteal injections precisely because it avoids the superior gluteal nerve. - This is the recommended injection site to prevent the complication that this patient experienced. - An injection here would not cause superior gluteal nerve injury or Trendelenburg gait. *Inferomedial quadrant of the buttock* - Injections in the **inferomedial quadrant** put the **sciatic nerve** at significant risk of injury. - Sciatic nerve injury would lead to symptoms affecting the posterior thigh and lower leg, such as **foot drop, loss of ankle reflexes, or paresthesias in the posterior leg and foot**, not isolated hip abductor weakness. *Inferolateral quadrant of the buttock* - This area is close to the **sciatic nerve** and **inferior gluteal nerve**. - Inferior gluteal nerve injury would affect the **gluteus maximus**, leading to difficulty with hip extension (trouble climbing stairs, rising from a chair), not a Trendelenburg gait. - Sciatic nerve injury would present with foot drop and sensory deficits. *Anteromedial thigh* - Injections in the **anteromedial thigh** could injure the **femoral nerve** or its branches. - This would cause **quadriceps weakness** with impaired knee extension and difficulty walking (buckling knee), not hip abductor weakness or Trendelenburg gait. - The femoral nerve does not control hip abduction.

Question 73: Seven hours after undergoing left hip arthroplasty for chronic hip pain, a 67-year-old woman reports a prickling sensation in her left anteromedial thigh and lower leg. Neurologic examination shows left leg strength 3/5 on hip flexion and 2/5 on knee extension. Patellar reflex is decreased on the left. Sensation to pinprick and light touch are decreased on the anteromedial left thigh as well as medial lower leg. Which of the following is the most likely underlying cause of this patient's symptoms?

A. Femoral nerve injury (Correct Answer)
B. L5 radiculopathy
C. Sural nerve injury
D. S1 radiculopathy
E. Fibular nerve injury

Explanation: ***Femoral nerve injury*** - The patient's symptoms—weakness in **hip flexion** (iliopsoas via femoral nerve) and **knee extension** (quadriceps via femoral nerve), decreased **patellar reflex** (femoral nerve), and sensory loss in the **anteromedial thigh** (femoral nerve) and **medial lower leg** (saphenous nerve, a branch of the femoral nerve)—are all consistent with femoral nerve dysfunction. - **Hip arthroplasty procedures** can sometimes lead to iatrogenic femoral nerve damage due to retraction, compression, or direct injury during surgery, especially when positioning or using surgical instruments. *L5 radiculopathy* - L5 radiculopathy typically causes weakness in **foot dorsiflexion**, **eversion**, and **toe extension**, along with sensory loss over the **dorsum of the foot** and lateral lower leg, which does not match the patient's presentation. - While it can cause hip abductor weakness, it would not explain the prominent **quadriceps weakness** and **decreased patellar reflex**. *Sural nerve injury* - The sural nerve provides sensation to the **posterolateral aspect of the lower leg** and lateral malleolus, and has no motor function to the hip or knee. - Injury to this nerve would not account for the patient's **proximal weakness** or sensory loss in the anteromedial thigh. *S1 radiculopathy* - S1 radiculopathy typically leads to weakness in **plantarflexion**, **hip extension**, and an absent **Achilles reflex**, along with sensory loss over the lateral foot and sole. - It would not explain the significant **quadriceps weakness**, **decreased patellar reflex**, or sensory changes in the anteromedial thigh. *Fibular nerve injury* - Fibular (peroneal) nerve injury primarily results in **foot drop** (weakness in dorsiflexion and eversion of the foot) and sensory loss over the **dorsum of the foot** and anterolateral lower leg. - It does not affect hip flexion, knee extension, or the patellar reflex, nor does it cause sensory loss in the anteromedial thigh.

Question 74: A 25-year-old man presents to the emergency department after a car accident. He was the front seat restrained driver in a head-on collision. He has no significant past medical history. The patient’s vitals are stabilized and he is ultimately discharged with his injuries appropriately treated. At the patient’s follow up primary care appointment, he complains of being unable to lift his left foot. He otherwise states that he feels well and is not in pain. His vitals are within normal limits. Physical exam is notable for 1/5 strength upon dorsiflexion of the patient’s left foot, and 5/5 plantarflexion of the same foot. Which of the following initial injuries most likely occurred in this patient?

A. Lisfranc fracture
B. Calcaneal fracture
C. Tibial plateau fracture
D. Distal femur fracture
E. Fibular neck fracture (Correct Answer)

Explanation: ***Fibular neck fracture*** - A fracture of the **fibular neck** can damage the **common peroneal nerve**, which wraps around this region. - Injury to the common peroneal nerve typically causes **foot drop** (inability to dorsiflex the foot) and sensory loss on the dorsum of the foot, matching the patient's symptoms of 1/5 strength upon dorsiflexion. *Lisfranc fracture* - This is an injury to the **midfoot tarsometatarsal joints**, often causing severe pain, swelling, and inability to bear weight. - While it can occur in high-impact trauma, it primarily affects the **structural integrity of the foot** and does not directly cause isolated foot drop through nerve damage. *Calcaneal fracture* - A fracture of the **heel bone** typically results from axial loading injuries (e.g., falls from height), causing severe heel pain, swelling, and gait disturbance. - It does not directly affect the common peroneal nerve or lead to isolated **foot drop**. *Tibial plateau fracture* - A fracture of the **proximal tibia** involves the knee joint and often results from significant valgus or varus force, presenting with knee pain, swelling, and instability. - While it can be associated with soft tissue injuries, isolated **foot drop** via common peroneal nerve injury is less directly linked than with a fibular neck fracture. *Distal femur fracture* - A fracture of the **lower part of the thigh bone** typically presents with severe pain, swelling, and deformity of the thigh and knee, often due to significant trauma. - This type of fracture is not directly associated with damage to the common peroneal nerve or isolated **foot drop**.

Question 75: A 21-year-old man comes to the physician for a follow-up examination. Four days ago, he injured his right knee while playing soccer. Increased laxity of the right knee joint is noted when the knee is flexed to 30° and an abducting force is applied to the lower leg. The examination finding in this patient is most likely caused by damage to which of the following structures?

A. Medial collateral ligament (Correct Answer)
B. Anterior cruciate ligament
C. Posterior cruciate ligament
D. Lateral collateral ligament
E. Lateral meniscus

Explanation: ***Medial collateral ligament*** - An abducting force applied to the lower leg (a **valgus stress**) when the knee is flexed to 30° tests the integrity of the MCL. Increased laxity indicates damage to this ligament. - The MCL resists **valgus stress** and is commonly injured in contact sports, especially when a force is applied to the outside of the knee. *Anterior cruciate ligament* - The **anterior drawer test** and **Lachman test** (anterior translation of the tibia with the knee flexed) are used to assess ACL integrity. - ACL injuries usually result from hyperextension, sudden stopping, or pivoting movements, leading to **anterior instability**. *Posterior cruciate ligament* - The **posterior drawer test** (posterior translation of the tibia with the knee flexed) is used to assess PCL integrity. - PCL injuries typically occur from a direct blow to the tibia or an anterior force on the tibia, indicating **posterior instability**. *Lateral collateral ligament* - The LCL is assessed by applying an **adducting force** to the lower leg (a **varus stress**). - Increased laxity during **varus stress** would indicate damage to the LCL. *Lateral meniscus* - Meniscal injuries are usually associated with clicking, locking, or catching sensations within the joint, and pain during twisting motions. - Meniscal tears are primarily diagnosed using specific provocative tests like **McMurray's test** or **Apley's grind test**, not by assessing ligamentous laxity with abducting forces.

Question 76: A 34-year-old woman comes to the physician because of a 3-month history of pain in her right thumb and wrist that radiates to her elbow. It is worse when she holds her infant son and improves with the use of an ice pack. Six months ago, she slipped on a wet floor and fell on her right outstretched hand. Her mother takes methotrexate for chronic joint pain. The patient takes ibuprofen as needed for her current symptoms. Examination of the right hand shows tenderness over the radial styloid with swelling but no redness. There is no crepitus. Grasping her right thumb and exerting longitudinal traction toward the ulnar side elicits pain. Range of motion of the finger joints is normal. There is no swelling, redness, or tenderness of any other joints. Which of the following is the most likely diagnosis?

A. De Quervain tenosynovitis (Correct Answer)
B. Carpal tunnel syndrome
C. Swan neck deformity
D. Mallet finger
E. Stenosing tenosynovitis

Explanation: ***De Quervain tenosynovitis*** - The patient's symptoms of **radial-sided wrist pain** radiating to the elbow, worsened by activities involving thumb movement (like holding her infant), and tenderness over the **radial styloid** are classic for De Quervain tenosynovitis. - The pain elicited by grasping the thumb and exerting traction toward the ulnar side (ulnar deviation of the wrist while the thumb is grasped - **Finkelstein's test**) is a pathognomonic finding for this condition. *Carpal tunnel syndrome* - Typically causes **numbness and tingling** in the thumb, index, middle, and radial half of the ring finger, often worse at night. - Pain is usually in the **volar wrist** and does not primarily involve the radial styloid or produce a positive Finkelstein's test. *Swan neck deformity* - Characterized by **hyperextension of the PIP joint** and flexion of the DIP joint of the fingers, resulting in a characteristic S-shaped appearance. - This is a **deformity** rather than an acute or subacute pain syndrome like the patient's presentation. *Mallet finger* - An injury to the **extensor tendon** of the finger, resulting in an inability to fully extend the DIP joint. - There is no mention of a traumatic injury to the DIP joint or a persistent flexion deformity in this patient. *Stenosing tenosynovitis* - Also known as **trigger finger**, it involves **tendon sheath inflammation** that restricts the smooth gliding of tendons, typically causing catching or locking of a finger. - This condition affects the **flexor tendons** and does not present with pain over the radial styloid or positive Finkelstein's test.

Question 77: A 37-year-old man presents to his primary care provider complaining of bilateral arm numbness. He was involved in a motor vehicle accident 3 months ago. His past medical history is notable for obesity and psoriatic arthritis. He takes adalimumab. His temperature is 99.3°F (37.4°C), blood pressure is 130/85 mmHg, pulse is 90/min, and respirations are 18/min. On exam, superficial skin ulcerations are found on his fingers bilaterally. His strength is 5/5 bilaterally in shoulder abduction, arm flexion, arm extension, wrist extension, finger abduction, and thumb flexion. He demonstrates loss of light touch and pinprick response in the distal tips of his 2nd and 5th fingertips and over the first dorsal web space. Vibratory sense is intact in the bilateral upper and lower extremities. Which of the following nervous system structures is most likely affected in this patient?

A. Cuneate fasciculus
B. Ventral horns
C. Anterior corticospinal tract
D. Spinocerebellar tract
E. Ventral white commissure (Correct Answer)

Explanation: ***Ventral white commissure*** - The patient presents with **bilateral loss of pain (pinprick) and light touch sensation** in the upper extremity fingertips, while **vibratory sense is intact** and **motor strength is fully preserved (5/5)**. This dissociated sensory loss pattern is pathognomonic for a lesion affecting the **ventral white commissure**. - The ventral white commissure contains **decussating fibers of the spinothalamic tract**, which carry pain and temperature sensation from the contralateral body. A lesion here (classically seen in **syringomyelia** affecting the cervical spinal cord) causes **bilateral loss of pain and temperature sensation** in a characteristic distribution while **sparing the dorsal columns** (vibratory sense and proprioception remain intact) and motor pathways. - The **superficial skin ulcerations** on his fingers are explained by chronic loss of protective pain sensation, leading to unnoticed repetitive trauma. The motor vehicle accident 3 months ago may have precipitated or worsened an underlying syrinx. - This is the classic **"cape-like" or suspended sensory loss** pattern, though it can present with focal dermatomal involvement as in this case. *Cuneate fasciculus* - The cuneate fasciculus is part of the **dorsal column-medial lemniscal pathway** that carries **vibratory sense, proprioception, and fine discriminative touch** from the upper extremities. - A lesion here would cause **loss of vibratory sense** and proprioception, which are explicitly **intact** in this patient, making this option incorrect. *Ventral horns* - The ventral horns contain **lower motor neuron cell bodies** that innervate skeletal muscles. - Damage would cause **motor deficits** including weakness (reduced strength), muscle atrophy, and fasciculations, none of which are present in this patient who has normal 5/5 strength throughout. *Anterior corticospinal tract* - This tract mediates **voluntary motor control**, primarily of axial and proximal muscles. - Lesions would result in **motor weakness or spasticity**, not the isolated sensory deficits seen in this patient. *Spinocerebellar tract* - The spinocerebellar tracts carry **unconscious proprioceptive information** to the cerebellum for motor coordination. - Damage would manifest as **ataxia, dysmetria, and incoordination**, which are not described in this patient's presentation.

Question 78: A 60-year-old woman is rushed to the emergency room after falling on her right elbow while walking down the stairs. She cannot raise her right arm. Her vital signs are stable, and the physical examination reveals loss of sensation over the upper lateral aspect of the right arm and shoulder. A radiologic evaluation shows a fracture of the surgical neck of the right humerus. Which of the following muscles is supplied by the nerve that is most likely damaged?

A. Teres minor (Correct Answer)
B. Teres major
C. Subscapularis
D. Infraspinatus
E. Supraspinatus

Explanation: ***Teres minor*** - A fracture of the **surgical neck of the humerus** often damages the **axillary nerve**, which innervates the **teres minor**. - The axillary nerve also supplies the **deltoid muscle** and provides cutaneous sensation to the **upper lateral arm**, consistent with the patient's sensory loss. *Teres major* - This muscle is innervated by the **lower subscapular nerve**, which is less likely to be damaged in a surgical neck fracture. - Its primary action is **adduction** and **internal rotation** of the arm. *Subscapularis* - The **subscapularis** is innervated by the **upper and lower subscapular nerves**. - While it contributes to internal rotation, its nerve supply is typically protected in this type of fracture. *Infraspinatus* - The **infraspinatus** muscle is innervated by the **suprascapular nerve**. - This nerve is generally not affected by a fracture of the surgical neck of the humerus. *Supraspinatus* - Similar to the infraspinatus, the **supraspinatus** is also innervated by the **suprascapular nerve**. - Damage to this nerve due to a humeral surgical neck fracture is uncommon.

Question 79: A 28-year-old man comes to the physician because of a 1-week history of weakness in the fingers of his right hand. One week ago, he experienced sudden pain in his right forearm during weight training. He has no history of serious illness. Physical examination shows impaired flexion of the proximal interphalangeal joints, while flexion of the distal interphalangeal joints is intact. Which of the following muscles is most likely injured?

A. Flexor carpi radialis
B. Flexor digitorum superficialis (Correct Answer)
C. Palmaris longus
D. Flexor carpi ulnaris
E. Flexor digitorum profundus

Explanation: **Flexor digitorum superficialis** - Injury to the **flexor digitorum superficialis (FDS)** accounts for the impaired flexion of the **proximal interphalangeal (PIP) joints** as it is the primary flexor of these joints. - The **intact flexion of the distal interphalangeal (DIP) joints** indicates that the **flexor digitorum profundus (FDP)**, which flexes the DIP joints, is still functional. *Flexor carpi radialis* - The **flexor carpi radialis** primarily acts to **flex and abduct the wrist**, not the finger joints. - An injury would lead to weakness in wrist movements rather than isolated finger joint flexion issues. *Palmaris longus* - The **palmaris longus** is a weak flexor of the wrist and tenses the **palmar aponeurosis**. - It does not contribute to the flexion of the interphalangeal joints of the fingers. *Flexor carpi ulnaris* - The **flexor carpi ulnaris** primarily **flexes and adducts the wrist**. - Injury to this muscle would result in wrist movement deficits, not specific interphalangeal joint flexion dysfunction. *Flexor digitorum profundus* - The **flexor digitorum profundus (FDP)** is responsible for **flexion of the distal interphalangeal (DIP) joints** as well as assisting with PIP and metacarpophalangeal (MCP) joint flexion. - Since flexion of the **DIP joints is intact**, the FDP is likely not injured.

Question 80: A 17-year-old boy comes to the physician because of a 3-month history of pain in his right shoulder. He reports that he has stopped playing for his high school football team because of persistent difficulty lifting his right arm. Physical examination shows impaired active abduction of the right arm from 0 to 15 degrees. After passive abduction of the right arm to 15 degrees, the patient is able to raise his arm above his head. The dysfunctional muscle in this patient is most likely to be innervated by which of the following nerves?

A. Long thoracic nerve
B. Suprascapular nerve (Correct Answer)
C. Upper subscapular nerve
D. Accessory nerve
E. Axillary nerve

Explanation: ***Suprascapular nerve*** - The patient exhibits impaired active abduction from 0 to 15 degrees but normal abduction after passive assistance, indicating dysfunction of the **supraspinatus muscle**. - The **supraspinatus muscle** is responsible for **initiating shoulder abduction** from 0 to 15 degrees, after which the deltoid muscle takes over for continued abduction. - The **suprascapular nerve** innervates both the **supraspinatus** and **infraspinatus muscles**, with the supraspinatus being crucial for the initial phase of abduction. *Long thoracic nerve* - This nerve innervates the **serratus anterior muscle**, which is responsible for **scapular protraction** and upward rotation. - Damage to the long thoracic nerve would typically result in **winged scapula**, not difficulty in initiating abduction. *Upper subscapular nerve* - The upper subscapular nerve innervates the **subscapularis muscle**, part of the rotator cuff. - This muscle is primarily involved in **internal rotation** of the shoulder and contributes to adduction, not abduction. *Accessory nerve* - The accessory nerve (cranial nerve XI) innervates the **sternocleidomastoid** and **trapezius muscles**. - Damage to this nerve would most likely present with weakness in **shrugging the shoulders** or turning the head, not difficulty with shoulder abduction. *Axillary nerve* - This nerve innervates the **deltoid muscle** and the **teres minor muscle**, and provides sensory input from the shoulder joint and lateral arm. - The deltoid is responsible for **shoulder abduction** from 15 to 90 degrees; a deficit here would affect a different range of motion than what is described.

Question 81: A 28-year-old man comes to the physician because of a 3-month history of pain in his left shoulder. He is physically active and plays baseball twice a week. The pain is reproduced when the shoulder is externally rotated against resistance. Injury of which of the following tendons is most likely in this patient?

A. Infraspinatus (Correct Answer)
B. Subscapularis
C. Pectoralis major
D. Supraspinatus
E. Teres major

Explanation: ***Infraspinatus*** - Pain during **external rotation against resistance** is a classic sign of infraspinatus tendon injury, as it is a primary muscle for this action. - The patient's history of playing baseball and experiencing pain, especially with resistive external rotation, points to an injury of this **rotator cuff muscle**. *Subscapularis* - The subscapularis primarily causes **internal rotation** of the shoulder; injury would typically present with pain during resisted internal rotation, not external. - While it is a rotator cuff muscle, its function does not align with the specific maneuver causing pain described in the patient. *Pectoralis major* - The pectoralis major is a large chest muscle involved primarily in **adduction**, **internal rotation**, and **flexion of the humerus**, not external rotation. - Injury to this muscle would present with pain during these specific movements, not resisted external rotation. *Supraspinatus* - The supraspinatus is primarily involved in **initiation of abduction** and helps stabilize the shoulder joint, and pain would usually be elicited during these movements. - While a common site of rotator cuff injury, its function does not directly cause pain with resisted external rotation as described. *Teres major* - The teres major acts as an **adductor** and **internal rotator** of the humerus, similar to the latissimus dorsi. - Pain from a teres major injury would be associated with these actions, not with resisted external rotation.

Question 82: A 34-year-old man is brought to the emergency department 3 hours after being bitten by a rattlesnake. He was hiking in the Arizona desert when he accidentally stepped on the snake and it bit his right leg. His pulse is 135/min and blood pressure is 104/81 mm Hg. Examination shows right lower leg swelling, ecchymosis, and blistering. Right ankle dorsiflexion elicits severe pain. A manometer inserted in the lateral compartment of the lower leg shows an intracompartmental pressure of 67 mm Hg. In addition to administration of the antivenom, the patient undergoes fasciotomy. Two weeks later, he reports difficulty in walking. Neurologic examination shows a loss of sensation over the lower part of the lateral side of the right leg and the dorsum of the right foot. Right foot eversion is 1/5. There is no weakness in dorsiflexion. Which of the following nerves is most likely injured in this patient?

A. Sural nerve
B. Tibial nerve
C. Saphenous nerve
D. Superficial peroneal nerve (Correct Answer)
E. Deep peroneal nerve

Explanation: ***Superficial peroneal nerve*** - The **superficial peroneal nerve** (also known as the superficial fibular nerve) is responsible for **foot eversion** (peroneus longus and brevis muscles) and provides sensory innervation to the **dorsum of the foot**, except for the web space between the first and second toes. - The patient's inability to evert the foot and sensory loss on the dorsum of the foot, combined with a history of **compartment syndrome** and fasciotomy in the lateral compartment, strongly indicates injury to the superficial peroneal nerve. *Sural nerve* - The **sural nerve** provides sensory innervation to the **posterolateral aspect of the lower leg** and the lateral aspect of the foot. - It does not innervate muscles involved in foot eversion or dorsiflexion, so its injury would not lead to the motor deficits described. *Tibial nerve* - The **tibial nerve** innervates the muscles of the posterior compartment of the leg, responsible for **plantarflexion** and inversion of the foot, and provides sensation to the sole of the foot. - Its injury would lead to weakness in plantarflexion and sensory loss on the sole, not the symptoms described. *Saphenous nerve* - The **saphenous nerve** is a pure sensory nerve, supplying sensation to the **medial aspect of the lower leg and foot**. - Its injury would result in sensory loss in this distribution but no motor deficits affecting foot eversion or dorsiflexion. *Deep peroneal nerve* - The **deep peroneal nerve** (also known as the deep fibular nerve) innervates the muscles of the anterior compartment of the leg, primarily responsible for **foot dorsiflexion** and toe extension, and provides sensation to the web space between the first and second toes. - The patient has no weakness in dorsiflexion, ruling out significant injury to the deep peroneal nerve.

Question 83: A 51-year-old woman comes to the physician because of progressively worsening lower back pain. The pain radiates down the right leg to the lateral side of the foot. She has had no trauma, urinary incontinence, or fever. An MRI of the lumbar spine shows disc degeneration and herniation at the level of L5–S1. Which of the following is the most likely finding on physical examination?

A. Difficulty walking on heels
B. Exaggerated patellar tendon reflex
C. Diminished sensation of the anus and genitalia
D. Diminished sensation of the anterior lateral thigh
E. Weak Achilles tendon reflex (Correct Answer)

Explanation: ***Weak Achilles tendon reflex*** - A herniated disc at **L5-S1** typically compresses the **S1 nerve root**, which is responsible for the **Achilles tendon reflex**. - **S1 radiculopathy** presents with weakness in plantarflexion, diminished or absent Achilles reflex, and sensory loss in the **lateral foot** (matching the patient's symptoms). *Difficulty walking on heels* - Difficulty walking on heels (**dorsiflexion weakness**) is primarily associated with **L4-L5 disc herniation** compressing the **L5 nerve root**. - This symptom indicates **L5 radiculopathy**, which affects the tibialis anterior muscle, not S1. *Exaggerated patellar tendon reflex* - An exaggerated patellar tendon reflex (**hyperreflexia**) indicates an **upper motor neuron lesion** or spinal cord compression above the lumbar region. - A disc herniation at **L5-S1** causes a **lower motor neuron lesion** with diminished reflexes, not hyperreflexia. *Diminished sensation of the anus and genitalia* - This symptom, along with urinary incontinence and saddle anesthesia, is characteristic of **cauda equina syndrome**, a surgical emergency. - The patient lacks urinary incontinence and the specific unilateral pain pattern points to isolated **S1 radiculopathy**, not cauda equina syndrome. *Diminished sensation of the anterior lateral thigh* - Sensory loss in the **anterior lateral thigh** is associated with compression of the **lateral femoral cutaneous nerve** or **L2-L4 nerve roots**. - This pattern is not consistent with **L5-S1 disc herniation**, which causes sensory changes in the lateral foot and posterior leg.

Question 84: A 10-year-old boy is referred to a pediatric neurologist by his pediatrician for lower extremity weakness. The boy is healthy with no past medical history, but his parents began to notice that he was having difficulty at football practice the previous day. Over the course of the past 24 hours, the boy has become increasingly clumsy and has been “tripping over himself.” On further questioning, the boy had a viral illness the previous week and was out of school for 2 days. Today, the patient’s temperature is 99.3°F (37.4°C), blood pressure is 108/72 mmHg, pulse is 88/min, respirations are 12/min. On motor exam, the patient has 5/5 strength in hip flexion, 5/5 strength in knee extension and flexion, 3/5 strength in foot dorsiflexion, and 5/5 strength in foot plantarflexion. The findings are the same bilaterally. On gait exam, the patient exhibits foot drop in both feet. Which of the following areas would the patient most likely have diminished sensation?

A. First dorsal webspace of foot (Correct Answer)
B. Lateral plantar foot
C. Anteromedial thigh
D. Medial plantar foot
E. Lateral foot

Explanation: ***First dorsal webspace of foot*** - The patient exhibits weakness in **foot dorsiflexion** and **foot drop**, which points to a lesion affecting the **deep fibular nerve** or its nerve roots (L4-L5). - The **first dorsal webspace** of the foot is the specific cutaneous sensory innervation area for the **deep fibular nerve**. *Lateral plantar foot* - The **lateral plantar nerve**, a branch of the tibial nerve, innervates this area. - Sensation here would be unlikely to be diminished given the primary motor deficits are related to dorsiflexion, which is supplied by the fibular nerve and not the tibial nerve. *Anteromedial thigh* - This area is primarily innervated by the **femoral nerve** (cutaneous branches) and the **obturator nerve**. - The patient's symptoms are in the lower leg and foot, making this area less likely to have affected sensation. *Medial plantar foot* - The **medial plantar nerve**, a branch of the tibial nerve, innervates this area. - Similar to the lateral plantar foot, this area is not directly related to the sensory distribution of the deep fibular nerve, which is responsible for dorsiflexion. *Lateral foot* - The **superficial fibular nerve** supplies sensation to the dorsum of the foot, excluding the first webspace, and the lateral lower leg. - While related to the fibular nerve, the most specific sensory loss with foot drop and deep fibular nerve involvement is the first dorsal webspace.

Question 85: An 18-year-old man comes to the clinic with his mom for “pins and needles” of both of his arms. He denies any past medical history besides a recent anterior cruciate ligament (ACL) tear that was repaired 1 week ago. The patient reports that the paresthesias are mostly located along the posterior forearms, left more than the right. What physical examination finding would you expect from this patient?

A. Loss of finger abduction
B. Loss of forearm flexion and supination
C. Loss of arm abduction
D. Loss of thumb opposition
E. Loss of wrist extension (Correct Answer)

Explanation: ***Loss of wrist extension*** - The patient describes "pins and needles" predominantly along the **posterior forearms**, indicating **radial nerve involvement**. - The **radial nerve** provides sensory innervation to the posterior forearm via the **posterior cutaneous nerve of the forearm**. - Motor function: The radial nerve innervates the **extensor carpi radialis longus and brevis** and **extensor carpi ulnaris**, which are responsible for **wrist extension**. - The recent **ACL repair surgery** suggests a **positional compression injury** to the radial nerves from prolonged arm positioning during the procedure. - Expected finding: **Wrist drop** (inability to extend the wrist against gravity). *Loss of finger abduction* - **Finger abduction** is controlled by the **interossei muscles**, which are innervated by the **ulnar nerve**. - The ulnar nerve provides sensory innervation to the **medial forearm** (via medial cutaneous nerve of forearm) and **medial 1.5 digits**, NOT the posterior forearm. - Posterior forearm paresthesias do not indicate ulnar nerve involvement. *Loss of forearm flexion and supination* - **Forearm flexion** is primarily controlled by the **musculocutaneous nerve** (supplying the **biceps brachii** and **brachialis**). - The musculocutaneous nerve becomes the **lateral cutaneous nerve of the forearm**, supplying the **lateral forearm**, not the posterior forearm. - Supination involves the biceps (musculocutaneous) and supinator (radial nerve, posterior interosseous branch). *Loss of arm abduction* - **Arm abduction** is primarily controlled by the **deltoid** muscle (innervated by the **axillary nerve**) and **supraspinatus** (suprascapular nerve). - Axillary nerve injury causes sensory loss over the **lateral shoulder** (regimental badge area), not the forearm. *Loss of thumb opposition* - **Thumb opposition** is a function of the **opponens pollicis** and **flexor pollicis brevis** (superficial head), primarily innervated by the **median nerve**. - Median nerve compression typically causes paresthesias in the **lateral 3.5 digits** and **thenar eminence**, not the posterior forearm.

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