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?
Q2
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?
Q3
A 13-year-old girl presents to an orthopedic surgeon for evaluation of a spinal curvature that was discovered during a school screening. She has otherwise been healthy and does not take any medications. On presentation, she is found to have significant asymmetry of her back and is sent for a spine radiograph. The radiograph reveals a unilateral rib attached to the left transverse process of the C7 vertebrae. Abnormal expression of which of the following genes is most likely responsible for this finding?
Q4
A 78-year-old woman is brought to the emergency department after she fell while gardening and experienced severe pain in her right arm. She has a history of well controlled hypertension and has been found to have osteoporosis. On presentation she is found to have a closed midshaft humerus fracture. No other major findings are discovered on a trauma survey. She is placed in a coaptation splint. The complication that is most associated with this injury has which of the following presentations?
Q5
A 56-year-old man presents to the emergency room after being in a motor vehicle accident. He was driving on an icy road when his car swerved off the road and ran head on into a tree. He complains of severe pain in his right lower extremity. He denies loss of consciousness during the accident. His past medical history is notable for poorly controlled hypertension, hyperlipidemia, and major depressive disorder. He takes enalapril, atorvastatin, and sertraline. His temperature is 99.1°F (37.3°C), blood pressure is 155/85 mmHg, pulse is 110/min, and respirations are 20/min. On exam, he is alert and fully oriented. He is unable to move his right leg due to pain. Sensation is intact to light touch in the sural, saphenous, tibial, deep peroneal, and superficial peroneal distributions. His leg appears adducted, flexed, and internally rotated. An anteroposterior radiograph of his pelvis would most likely demonstrate which of the following findings?
Q6
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?
Q7
A 25-year-old woman is brought to the emergency department after being involved in a rear-end collision, in which she was the restrained driver of the back car. On arrival, she is alert and active. She reports pain in both knees and severe pain over the right groin. Temperature is 37°C (98.6°F), pulse is 116/min, respirations are 19/min, and blood pressure is 132/79 mm Hg. Physical examination shows tenderness over both knee caps. The right groin is tender to palpation. The right leg is slightly shortened, flexed, adducted, and internally rotated. The remainder of the examination shows no abnormalities. Which of the following is the most likely diagnosis?
Q8
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?
Q9
A 30-year-old male presents with pain and limited movement in his shoulder following a fall. X-ray reveals an anterior dislocation of the glenohumeral joint. Which of the following structures is most likely to be damaged in this injury?
Q10
A 61-year-old man is brought to the emergency department because of increasing weakness of his right arm and leg that began when he woke up that morning. He did not notice any weakness when he went to bed the night before. He has hypertension and hypercholesterolemia. Current medications include hydrochlorothiazide and atorvastatin. He is alert and oriented to person, time, place. His temperature is 36.7°C (98°F), pulse is 91/min, and blood pressure is 132/84 mm Hg. Examination shows drooping of the right side of the face. Muscle strength is decreased in the right upper and lower extremities. Deep tendon reflexes are 4+ on the right side. Sensation is intact. His speech is normal in rate and rhythm. The remainder of the examination shows no abnormalities. An infarction of which of the following sites is the most likely cause of this patient's symptoms?
Comparison of upper and lower limb structures US Medical PG Practice Questions and MCQs
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
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.
Question 2: 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 3: A 13-year-old girl presents to an orthopedic surgeon for evaluation of a spinal curvature that was discovered during a school screening. She has otherwise been healthy and does not take any medications. On presentation, she is found to have significant asymmetry of her back and is sent for a spine radiograph. The radiograph reveals a unilateral rib attached to the left transverse process of the C7 vertebrae. Abnormal expression of which of the following genes is most likely responsible for this finding?
A. WNT7
B. FGF
C. Homeobox (Correct Answer)
D. PAX
E. Sonic hedgehog
Explanation: ***Homeobox***
- **Homeobox genes (HOX genes)** play a crucial role in specifying the identity of vertebral segments along the **craniocaudal axis** during embryonic development.
- An abnormal expression of these genes can lead to **skeletal malformations**, such as the formation of a **cervical rib**, by altering the segmental identity of the C7 vertebra.
*WNT7*
- **WNT7 genes** are involved in limb patterning and have a role in the formation of the **dorsoventral axis** of the limb and kidney development.
- They are not primarily associated with vertebral segmentation or the formation of cervical ribs.
*FGF*
- **Fibroblast growth factor (FGF) genes** are essential for various processes, including limb development, neurogenesis, and angiogenesis.
- While they are involved in numerous developmental pathways, they are not the primary genes responsible for specifying vertebral identity and thus cervical rib formation.
*PAX*
- **PAX genes** are a family of transcription factors critical for organ development, especially of the eye, brain, and kidney.
- While important for development, they are not directly implicated in the specification of vertebral segments or the pathogenesis of cervical ribs.
*Sonic hedgehog*
- **Sonic hedgehog (SHH)** signaling is a key pathway in embryonic development, particularly for pattern formation in the neural tube, limbs, and facial structures.
- While crucial for body axis development and segmentation, **HOX genes** have a more direct role in determining the specific identity of vertebral segments and causing cervical ribs.
Question 4: A 78-year-old woman is brought to the emergency department after she fell while gardening and experienced severe pain in her right arm. She has a history of well controlled hypertension and has been found to have osteoporosis. On presentation she is found to have a closed midshaft humerus fracture. No other major findings are discovered on a trauma survey. She is placed in a coaptation splint. The complication that is most associated with this injury has which of the following presentations?
A. Hand of benediction
B. Hypothenar atrophy
C. Flattened deltoid
D. Elbow flexion deficits
E. Wrist drop (Correct Answer)
Explanation: ***Wrist drop***
- A **midshaft humerus fracture** is classically associated with injury to the **radial nerve**, which wraps around the humerus at this level.
- **Radial nerve injury** causes paralysis of the extensors of the wrist and fingers, leading to a characteristic **wrist drop** presentation.
*Hand of benediction*
- This presentation, where the **index and middle fingers remain extended** while the ring and little fingers flex, is characteristic of a **proximal median nerve injury**.
- A midshaft humerus fracture is less likely to cause a proximal median nerve injury given the anatomical course of the nerve.
*Hypothenar atrophy*
- **Hypothenar atrophy** is indicative of **ulnar nerve damage**, usually at the cubital tunnel or Guyon's canal.
- While the ulnar nerve courses near the humerus, it is less commonly injured in midshaft fractures compared to the radial nerve.
*Flattened deltoid*
- A **flattened deltoid** is a sign of **axillary nerve injury** or shoulder dislocation, leading to paralysis of the deltoid muscle.
- The axillary nerve is more commonly injured in **proximal humerus fractures** or shoulder trauma, not typically midshaft fractures.
*Elbow flexion deficits*
- **Elbow flexion deficits** are primarily associated with injury to the **musculocutaneous nerve** or the C5/C6 nerve roots.
- While a severe humeral fracture could potentially affect these structures, it is not the most direct or common neurological complication of a midshaft fracture, which targets the radial nerve.
Question 5: A 56-year-old man presents to the emergency room after being in a motor vehicle accident. He was driving on an icy road when his car swerved off the road and ran head on into a tree. He complains of severe pain in his right lower extremity. He denies loss of consciousness during the accident. His past medical history is notable for poorly controlled hypertension, hyperlipidemia, and major depressive disorder. He takes enalapril, atorvastatin, and sertraline. His temperature is 99.1°F (37.3°C), blood pressure is 155/85 mmHg, pulse is 110/min, and respirations are 20/min. On exam, he is alert and fully oriented. He is unable to move his right leg due to pain. Sensation is intact to light touch in the sural, saphenous, tibial, deep peroneal, and superficial peroneal distributions. His leg appears adducted, flexed, and internally rotated. An anteroposterior radiograph of his pelvis would most likely demonstrate which of the following findings?
A. Fracture line extending between the greater and lesser trochanters
B. Femoral head larger than contralateral side and inferior to acetabulum
C. Fracture line extending through the femoral neck
D. Fracture line extending through the subtrochanteric region of the femur
E. Femoral head smaller than contralateral side and posterior to acetabulum (Correct Answer)
Explanation: ***Femoral head smaller than contralateral side and posterior to acetabulum***
- This presentation is consistent with a **posterior hip dislocation**, which typically occurs with an **axial load** on a flexed hip, common in head-on collisions.
- On radiographs, the femoral head appears **smaller** due to magnification differences and is displaced **posteriorly** relative to the acetabulum. The affected leg is classically **shortened, adducted, and internally rotated**.
*Fracture line extending between the greater and lesser trochanters*
- This describes an **intertrochanteric hip fracture**, which typically presents with the leg **externally rotated** and **abducted**, not internally rotated and adducted.
- While caused by trauma, the clinical presentation does not align with the patient's physical exam findings.
*Femoral head larger than contralateral side and inferior to acetabulum*
- This describes an **anterior hip dislocation**, which is far less common and would present with the leg typically held in **abduction** and **external rotation**. The femoral head would also appear **larger** due to magnification from being anteriorly displaced.
- The patient's presentation of adduction and internal rotation is inconsistent with an anterior dislocation.
*Fracture line extending through the femoral neck*
- A **femoral neck fracture** usually presents with the leg in **external rotation** and **shortening**, and often involves older patients with osteoporosis after falls.
- While a severe impact could cause this, the characteristic adduction and internal rotation point more strongly to a dislocation.
*Fracture line extending through the subtrochanteric region of the femur*
- A **subtrochanteric fracture** involves the shaft of the femur just below the trochanters and commonly presents with significant pain and inability to bear weight.
- This type of fracture does not typically result in the specific adducted and internally rotated leg position seen with hip dislocations.
Question 6: 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 7: A 25-year-old woman is brought to the emergency department after being involved in a rear-end collision, in which she was the restrained driver of the back car. On arrival, she is alert and active. She reports pain in both knees and severe pain over the right groin. Temperature is 37°C (98.6°F), pulse is 116/min, respirations are 19/min, and blood pressure is 132/79 mm Hg. Physical examination shows tenderness over both knee caps. The right groin is tender to palpation. The right leg is slightly shortened, flexed, adducted, and internally rotated. The remainder of the examination shows no abnormalities. Which of the following is the most likely diagnosis?
A. Anterior hip dislocation
B. Posterior hip dislocation (Correct Answer)
C. Femoral neck fracture
D. Pelvic fracture
E. Femoral shaft fracture
Explanation: ***Posterior hip dislocation***
- The classic presentation of **posterior hip dislocation** involves the affected leg being **shortened, flexed, adducted, and internally rotated**, as described in the patient.
- This type of injury commonly occurs in **motor vehicle collisions** where the knee strikes the dashboard (dashboard injury), transmitting force up the femur to the hip joint, often causing the femoral head to dislocate posteriorly.
*Anterior hip dislocation*
- This typically presents with the affected leg in a position of **hip flexion, abduction, and external rotation**, which is contrary to the findings in this patient.
- Anterior dislocations are less common than posterior dislocations and usually result from a traumatic force applied to the hip while it is in **abduction and external rotation**.
*Femoral neck fracture*
- While a **femoral neck fracture** can cause pain and shortening of the leg, the typical presentation is usually one of **external rotation**, not internal rotation.
- The distinct **flexion, adduction, and internal rotation** triad is highly suggestive of hip dislocation, not a fracture of the femoral neck.
*Pelvic fracture*
- A **pelvic fracture** would likely present with more diffuse pelvic pain, potentially instability upon palpation of the pelvis, and possibly lower extremity neurological deficits or genitourinary symptoms depending on the fracture type.
- The specific limb positioning observed (shortened, flexed, adducted, internally rotated) is not a hallmark of an isolated pelvic fracture.
*Femoral shaft fracture*
- A **femoral shaft fracture** would cause severe pain along the shaft of the femur, significant swelling, and obvious deformity of the thigh.
- While the leg might be shortened, the specific combination of **flexion, adduction, and internal rotation** primarily points towards a hip joint issue rather than a mid-shaft fracture.
Question 8: 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 9: A 30-year-old male presents with pain and limited movement in his shoulder following a fall. X-ray reveals an anterior dislocation of the glenohumeral joint. Which of the following structures is most likely to be damaged in this injury?
A. Long head of biceps tendon
B. Acromioclavicular ligament
C. Supraspinatus tendon
D. Anterior inferior glenohumeral ligament (Correct Answer)
E. Coracoclavicular ligament
Explanation: ***Anterior inferior glenohumeral ligament***
- This ligament is a primary static stabilizer against **anterior dislocation** of the shoulder; thus, it is frequently stretched or torn during such an event.
- Damage to this ligament is often associated with a **Bankart lesion**, which is an injury to the anterior inferior labrum that can lead to recurrent dislocations.
*Long head of biceps tendon*
- While the **long head of the biceps tendon** can be injured in shoulder trauma, it is more commonly associated with chronic overuse or superior labral tears (**SLAP lesions**), rather than primary anterior dislocation.
- Injuries to this tendon might occur as a secondary complication but are not the most likely primary soft tissue damage in an acute anterior dislocation.
*Acromioclavicular ligament*
- The **acromioclavicular ligament** stabilizes the **acromioclavicular (AC) joint**, which is distinct from the glenohumeral joint.
- Injuries to this ligament typically result from direct trauma to the top of the shoulder, causing AC joint separation, not glenohumeral dislocation.
*Supraspinatus tendon*
- The **supraspinatus tendon** is part of the rotator cuff and is most commonly injured in impingement syndrome or rotator cuff tears, which can result from falls but are not the primary structure damaged in an **anterior glenohumeral dislocation**.
- Its role is mainly in abduction of the arm, and while it can be involved in large tears associated with advanced age, it is not the initial or most common structure to fail in this specific injury.
*Coracoclavicular ligament*
- The **coracoclavicular ligament** is composed of the conoid and trapezoid ligaments, which are crucial for the stability of the **acromioclavicular (AC) joint**.
- Injury to this ligament is indicative of a more severe AC joint separation (usually **type III or higher**) and is not the primary structure damaged in a glenohumeral dislocation.
Question 10: A 61-year-old man is brought to the emergency department because of increasing weakness of his right arm and leg that began when he woke up that morning. He did not notice any weakness when he went to bed the night before. He has hypertension and hypercholesterolemia. Current medications include hydrochlorothiazide and atorvastatin. He is alert and oriented to person, time, place. His temperature is 36.7°C (98°F), pulse is 91/min, and blood pressure is 132/84 mm Hg. Examination shows drooping of the right side of the face. Muscle strength is decreased in the right upper and lower extremities. Deep tendon reflexes are 4+ on the right side. Sensation is intact. His speech is normal in rate and rhythm. The remainder of the examination shows no abnormalities. An infarction of which of the following sites is the most likely cause of this patient's symptoms?
A. Base of the left pons
B. Left cerebellar vermis
C. Left posterolateral thalamus
D. Posterior limb of the left internal capsule (Correct Answer)
E. Left lateral medulla
Explanation: ***Posterior limb of the left internal capsule***
- The patient presents with sudden onset of **right-sided weakness**, including the face, arm, and leg (hemiparesis), consistent with a **pure motor stroke**.
- The **posterior limb of the internal capsule** contains UMN fibers of the **corticospinal and corticobulbar tracts**, which project to the contralateral side of the body, thus lesions here cause contralateral pure motor deficits.
*Base of the left pons*
- A lesion here would typically cause **contralateral hemiparesis or hemiplegia** (right side in this case).
- However, pontine lesions also often include **cranial nerve palsies** (e.g., abducens or facial nerve) or **ataxia**, which are not described.
*Left cerebellar vermis*
- Damage to the cerebellar vermis primarily results in **truncal ataxia** and disorders of gait and balance.
- It would not cause contralateral hemiparesis or facial droop, as seen in this patient.
*Left posterolateral thalamus*
- An infarct in this area would primarily cause **contralateral sensory deficits**, such as hemianesthesia or dysesthesia.
- While motor deficits can occur, they are typically less prominent than sensory issues and would not be the isolated pure motor syndrome described.
*Left lateral medulla*
- A lesion in the lateral medulla (e.g., Wallenberg syndrome) typically presents with **contralateral pain and temperature loss**, ipsilateral Horner's syndrome, ataxia, and dysphagia.
- It would not manifest as an isolated pure motor hemiparesis.
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