Motor testing of myotomes US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Motor testing of myotomes. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Motor testing of myotomes US Medical PG Question 1: A 16-year-old boy is brought to the emergency department after being tackled at a football game. Per his mom, he is the quarterback of his team and was head-butted in the left shoulder region by the opposing team. Shortly after, the mother noticed that his left arm was hanging by his torso and his hand was “bent backwards and facing the sky.” The patient denies head trauma, loss of consciousness, sensory changes, or gross bleeding. A physical examination demonstrates weakness in abduction, lateral rotation, flexion, and supination of the left arm and tenderness of the left shoulder region with moderate bruising. Radiograph of the left shoulder and arm is unremarkable. Which of the following is most likely damaged in this patient?
- A. C5-C6 nerve roots (Correct Answer)
- B. Ulnar nerve
- C. C8-T1 nerve roots
- D. Long thoracic nerve
Motor testing of myotomes Explanation: ***C5-C6 nerve roots***
- The "bent backwards and facing the sky" hand posture indicates **Waiter's tip position**, a classic sign of **Erb-Duchenne palsy**, caused by damage to the upper trunk of the brachial plexus (C5-C6 roots) [1].
- Weakness in **abduction** (deltoid, supraspinatus), **lateral rotation** (infraspinatus, teres minor), **flexion** (biceps, coracobrachialis), and **supination** (biceps, supinator) are all consistent with C5-C6 nerve root involvement.
*Ulnar nerve*
- Ulnar nerve damage would result in a **claw hand deformity** (hyperextension of MCP joints and flexion of DIP/PIP joints of 4th and 5th digits) and weakness in intrinsic hand muscles, not the observed upper arm weakness.
- Sensory loss involves the medial hand and little finger.
*C8-T1 nerve roots*
- Damage to the C8-T1 nerve roots (lower trunk) typically results in **Klumpke's palsy**, characterized by a more severe **claw hand** and paralysis of intrinsic hand muscles [1].
- This presentation does not match the observed functional deficits.
*Long thoracic nerve*
- Injury to the long thoracic nerve causes paralysis of the **serratus anterior muscle**, leading to **scapular winging**, especially when pushing against a wall.
- While possible in shoulder trauma, it does not explain the widespread weakness in abduction, rotation, flexion, and supination of the arm.
Motor testing of myotomes US Medical PG Question 2: 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)
Motor testing of myotomes 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.
Motor testing of myotomes US Medical PG Question 3: A 29-year-old woman presents to the primary care office for a recent history of falls. She has fallen 5 times over the last year. These falls are not associated with any preceding symptoms; she specifically denies dizziness, lightheadedness, or visual changes. However, she has started noticing that both of her legs feel weak. She's also noticed that her carpet feels strange beneath her bare feet. Her mother and grandmother have a history of similar problems. On physical exam, she has notable leg and foot muscular atrophy and 4/5 strength throughout her bilateral lower extremities. Sensation to light touch and pinprick is decreased up to the mid-calf. Ankle jerk reflex is absent bilaterally. Which of the following is the next best diagnostic test for this patient?
- A. MRI brain
- B. Ankle-brachial index
- C. Electromyography (including nerve conduction studies) (Correct Answer)
- D. Lumbar puncture
- E. Hemoglobin A1c
Motor testing of myotomes Explanation: ***Electromyography (including nerve conduction studies)***
- The patient's symptoms of **progressive weakness**, **sensory deficits** (carpet feels strange, decreased sensation up to mid-calf), **muscular atrophy**, and **absent ankle reflexes**, along with a **family history**, are highly suggestive of a **hereditary peripheral neuropathy** (e.g., Charcot-Marie-Tooth disease).
- **Electromyography (EMG)** and **nerve conduction studies (NCS)** are essential for confirming peripheral neuropathy, differentiating between demyelinating and axonal involvement, and localizing the lesion.
*MRI brain*
- An MRI brain would be indicated for central nervous system pathology, but the patient's symptoms (distal weakness, sensory loss with a "stocking-glove" distribution, absent reflexes) are highly suggestive of a **peripheral neuropathy**.
- There is no indication of upper motor neuron signs or other CNS involvement to warrant a brain MRI at this stage.
*Ankle-brachial index*
- Ankle-brachial index (ABI) is used to diagnose **peripheral artery disease (PAD)**, which typically presents with claudication (pain with exertion) and ischemic changes.
- The patient's symptoms of sensory changes and progressive weakness are not characteristic of PAD.
*Lumbar puncture*
- A lumbar puncture is primarily used to analyze **cerebrospinal fluid (CSF)** for inflammatory, infectious, or neoplastic conditions affecting the CNS or nerve roots (e.g., Guillain-Barré syndrome, which has acute onset).
- Given the chronic and progressive nature of her symptoms and a positive family history, it is less likely to be an acute inflammatory process of the nerve roots.
*Hemoglobin A1c*
- Hemoglobin A1c is used to screen for or monitor **diabetes mellitus**, which can cause a **diabetic neuropathy**.
- While diabetes can cause peripheral neuropathy, the patient's young age, lack of typical diabetic risk factors, and strong family history point more strongly towards a hereditary condition. Glycemic control does not fully explain her presentation.
Motor testing of myotomes US Medical PG Question 4: 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)
Motor testing of myotomes 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.
Motor testing of myotomes US Medical PG Question 5: An MRI of a patient with low back pain reveals compression of the L5 nerve root. Which of the following muscles would most likely show weakness during physical examination?
- A. Tibialis posterior
- B. Tibialis anterior (Correct Answer)
- C. Gastrocnemius
- D. Quadriceps femoris
Motor testing of myotomes Explanation: ***Tibialis anterior***
- The **L5 nerve root** primarily innervates muscles responsible for **dorsiflexion** of the foot, with the **tibialis anterior** being the primary dorsiflexor.
- Weakness of the tibialis anterior would manifest as difficulty lifting the front of the foot, potentially leading to a **foot drop** gait.
*Tibialis posterior*
- The **tibialis posterior** is primarily innervated by the **tibial nerve** (S1-S2) and is responsible for **plantarflexion** and **inversion** of the foot.
- Weakness in this muscle would not be the most likely presentation of L5 nerve root compression.
*Gastrocnemius*
- The **gastrocnemius** muscle is primarily innervated by the **tibial nerve** (S1-S2) and is a powerful **plantarflexor** of the foot.
- Weakness in this muscle would indicate an S1 or S2 nerve root issue, not typically L5.
*Quadriceps femoris*
- The **quadriceps femoris** is innervated by the **femoral nerve**, predominantly originating from the **L2, L3, and L4 nerve roots**.
- Weakness would manifest as difficulty extending the knee, which is not characteristic of L5 compression.
Motor testing of myotomes US Medical PG Question 6: A 59-year-old woman presents to the emergency room with severe low back pain. She reports pain radiating down her left leg into her left foot. She also reports intermittent severe lower back spasms. The pain started after lifting multiple heavy boxes at her work as a grocery store clerk. She denies bowel or bladder dysfunction. Her past medical history is notable for osteoporosis and endometrial cancer. She underwent a hysterectomy 20 years earlier. She takes alendronate. Her temperature is 99°F (37.2°C), blood pressure is 135/85 mmHg, pulse is 85/min, and respirations are 22/min. Her BMI is 21 kg/m^2. On exam, she is unable to bend over due to pain. Her movements are slowed to prevent exacerbating her muscle spasms. A straight leg raise elicits severe radiating pain into her left lower extremity. The patient reports that the pain is worst along the posterior thigh and posterolateral leg into the fourth and fifth toes. Palpation along the lumbar vertebral spines demonstrates mild tenderness. Patellar reflexes are 2+ bilaterally. The Achilles reflex is decreased on the left. Which nerve root is most likely affected in this patient?
- A. L5
- B. S2
- C. L3
- D. L4
- E. S1 (Correct Answer)
Motor testing of myotomes Explanation: ***S1***
- Pain radiating to the **posterior thigh**, **posterolateral leg**, and into the **fourth and fifth toes** is characteristic of **S1 dermatome involvement**.
- A **decreased Achilles reflex** (ankle jerk reflex) specifically points to compromise of the **S1 nerve root**.
*L5*
- **L5 radiculopathy** typically causes pain and sensory deficits in the **dorsum of the foot** and into the **first, second, and third toes**.
- Motor weakness often affects **foot dorsiflexion** and **toe extension**, not primarily the Achilles reflex.
*S2*
- **S2 radiculopathy** would primarily affect sensation along the **posterior thigh** and **calf**, with possible involvement of the **plantar aspect of the foot**.
- It does not typically cause a decrease in the **Achilles reflex**, which is predominantly S1.
*L3*
- **L3 radiculopathy** typically presents with pain and sensory changes along the **anterior thigh** and possibly the **medial knee**.
- It can affect the **patellar reflex**, which is intact in this patient, and does not cause pain in the posterior leg or foot.
*L4*
- **L4 radiculopathy** typically causes pain and sensory changes over the **anterior thigh**, **medial leg**, and potentially the **medial malleolus**.
- It often presents with weakness in **quadriceps muscle** and can cause a diminished **patellar reflex**, which is normal in this patient.
Motor testing of myotomes US Medical PG Question 7: 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
Motor testing of myotomes 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.
Motor testing of myotomes US Medical PG Question 8: 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
Motor testing of myotomes 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.
Motor testing of myotomes US Medical PG Question 9: 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)
Motor testing of myotomes 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.
Motor testing of myotomes US Medical PG Question 10: 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
Motor testing of myotomes 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.
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