DFT-18/09/2025-ANATOMY D4

A 34-year-old carpenter presents with a three-week history of weakness in his dominant right hand. He struggles to pick up nails and cannot make an "OK" sign, noting his thumb and index finger form a "pinch" grip instead of a circle. There are no sensory deficits. Electromyography confirms an isolated neuropathy of the anterior interosseous nerve. Besides the flexor pollicis longus and the lateral half of the flexor digitorum profundus, which muscle, identified in the deep distal forearm, is also denervated?

• Pronator Quadratus

• Pronator Teres

• Flexor Carpi Ulnaris

  
  

•  Brachioradialis

Answer explanation

The anterior interosseous nerve (AIN) is a pure motor branch of the median nerve that innervates the pronator quadratus, flexor pollicis longus, and the radial part of the flexor digitorum profundus, matching the patient's clinical presentation.

A 52-year-old avid tennis player presents with insidious-onset pain over the medial aspect of his left elbow, worsened by his forehand stroke. Examination reveals marked tenderness just distal to the medial epicondyle. The pain is exacerbated on resisted wrist flexion and forearm pronation. This presentation is classic for medial epicondylitis, which involves inflammation of the common flexor tendon. Which of the following muscles originates from the lateral supracondylar ridge and forms the lateral boundary of the cubital fossa, making it anatomically distinct from the group of muscles implicated in this pathology?

•  Brachioradialis

  
  

•  Pronator Teres

• Flexor Carpi Radialis

• Palmaris Longus

  
  

Answer explanation

Brachioradialis originates from the lateral supracondylar ridge of the humerus and forms the lateral border of the cubital fossa. It is not part of the common flexor origin involved in medial epicondylitis ("golfer's elbow").

A 45-year-old carpenter presents with acute, deep pain in his proximal forearm after a day of extensively using a manual screwdriver. He reports a sudden inability to make a perfect "O" sign with his thumb and index finger. Examination reveals weakness in flexion of the distal interphalangeal (DIP) joint of the index finger and the interphalangeal (IP) joint of the thumb. Sensation over the entire hand is normal. Which of the following is the most likely diagnosis explaining this specific motor deficit?

• Anterior interosseous nerve (AIN) syndrome

  
  

• Pronator teres syndrome

• Ulnar nerve entrapment at the cubital tunnel

• C8 radiculopathy

Answer explanation

The anterior interosseous nerve, a pure motor branch of the median nerve, innervates the flexor pollicis longus (FPL) and the lateral half of the flexor digitorum profundus (FDP). Its compression leads to the characteristic "pinch sign" deficit.

A 30-year-old patient sustains a deep laceration to the volar wrist, positioned anatomically between the palmaris longus and flexor carpi ulnaris tendons. Neurological assessment reveals an inability to abduct or adduct the fingers and sensory loss over the medial one-and-a-half digits.

Based on the most probable nerve injury, which muscle's function would be completely spared?

•  First lumbrical

  
  

• Third palmar interosseous

• Abductor digiti minimi

• Adductor pollicis

Answer explanation

The injury described is classic for a transection of the ulnar nerve at the wrist. The first lumbrical is innervated by the median nerve, which would be spared, thus its function would remain completely intact.

From a purely anatomical and functional standpoint, which statement most accurately describes the intrinsic interosseous muscles of the hand?

• The four bipennate dorsal interossei are primarily responsible for finger abduction (DAB), while the three unipennate palmar interossei execute adduction (PAD).

• The four unipennate dorsal interossei abduct the digits, whereas the three bipennate palmar interossei adduct them.

•  All seven interossei are bipennate, innervated by the median nerve, and primarily function to extend the interphalangeal joints.

  
  

• There are three dorsal interossei and four palmar interossei, all of which are innervated by the radial nerve and function to flex the metacarpophalangeal joints.

  
  

Answer explanation

The mnemonic 'DAB' (Dorsal Abduct) and 'PAD' (Palmar Adduct) is key. There are four bipennate dorsal interossei and three unipennate palmar interossei, reflecting their respective functional demands for abduction and adduction.

During a radical mastectomy procedure for breast carcinoma, the surgeon must carefully preserve the arterial supply to the serratus anterior muscle to prevent its iatrogenic paralysis and subsequent "winging" of the scapula. Which vessel, originating from the second part of the axillary artery, is paramount to preserve for this purpose?

• Lateral thoracic artery

• Thoracoacromial artery

• Subscapular artery

• Dorsal scapular artery

Answer explanation

The lateral thoracic artery typically runs along the lateral border of the pectoralis minor, directly supplying the overlying serratus anterior muscle. Its ligation can lead to ischemic injury of the muscle.

A 22-year-old rugby player sustains a forceful abduction and external rotation injury to his right arm, resulting in an anterior glenohumeral dislocation. Post-reduction, he exhibits marked deltoid weakness and hypoesthesia over the "regimental badge" area. An urgent angiogram is performed due to an expanding axillary hematoma, which reveals a pseudoaneurysm. Which artery, arising from the third part of the axillary artery, is most likely compromised?

• Posterior circumflex humeral artery

• Subscapular artery

• Thoracoacromial artery

• Superior thoracic artery

Answer explanation

The posterior circumflex humeral artery and the axillary nerve pass together through the quadrangular space and are in intimate contact with the surgical neck of the humerus, making them highly vulnerable to injury in anterior dislocations.

A 24-year-old motorcyclist is brought to the emergency department after being thrown from his vehicle, landing forcefully on the point of his right shoulder. This mechanism caused extreme lateral flexion of his neck to the contralateral side. On examination, his right upper limb is held in adduction and internal rotation, with the elbow extended and forearm pronated. He also reports sensory loss over the "regimental badge" area. Which neurological structure is most likely compromised at its origin?

• Superior trunk

• Posterior cord

• Medial cord

  
  

• Radial nerve in the spiral groove

Answer explanation

The mechanism describes a traction injury to the C5-C6 nerve roots, which unite to form the superior trunk. This results in the classic Erb-Duchenne palsy, or "waiter's tip" posture, with paralysis of shoulder abductors/external rotators and elbow flexors.

A 35-year-old rock climber loses his grip and momentarily hangs by his right arm from a ledge before being rescued. In the following days, he develops weakness in his right hand, specifically with finger abduction and adduction. He also notes a loss of sensation along the medial border of his forearm and hand. On physical examination, a mild drooping of his right eyelid is observed. Which component of the brachial plexus is most likely injured?

• Inferior trunk (C8, T1)

  
  

• Lateral cord (C5, C6, C7)

•  Musculocutaneous nerve

•  Suprascapular nerve

Answer explanation

The hyperabduction injury mechanism causes traction on the C8 and T1 nerve roots, forming the inferior trunk. This results in Klumpke's palsy (intrinsic hand muscle paralysis) and associated Horner's syndrome due to sympathetic fiber disruption.

A 28-year-old male presents to the trauma center after a high-speed motorcycle collision where he was thrown from his vehicle, landing forcefully on the point of his right shoulder and neck. Physical examination reveals his right arm is held in adduction and internal rotation, with the elbow extended and the forearm pronated. He demonstrates a significant loss of shoulder abduction and elbow flexion. Sensation is diminished over the regimental badge area. Which single neurological structure is most likely injured?

• Superior trunk

• Posterior cord

•  Musculocutaneous nerve

  
  

• C8 and T1 nerve roots

Answer explanation

This classic "waiter's tip" posture results from an injury to the C5 and C6 nerve roots, which unite to form the superior trunk. This lesion affects the axillary, suprascapular, and musculocutaneous nerves, paralyzing key shoulder and arm muscles.