WBR0503
| Author | [[PageAuthor::Ayokunle Olubaniyi, M.B,B.S [1]]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Anatomy |
| Sub Category | |
| Prompt | [[Prompt::A 4-year-old girl is brought to the emergency department by her mother because of severe pain in her left hand. The girl was playing with her friends in her backyard and fell, breaking the fall with her outstretched hand. There was a transient loss of wrist flexion as well as loss of sensation over the hypothenar eminence. Physical examination revealed a young girl, in painful distress, and holding her left elbow. X-ray of the left hand revealed no fractures.
Which of the following nerves is implicated?]] |
| Answer A | AnswerA::Ulnar nerve |
| Answer A Explanation | [[AnswerAExp::Correct. Damage to the ulnar nerve causes to loss of wrist flexion, adduction and abduction of the fingers, and extension of the thumb.]] |
| Answer B | AnswerB::Radial nerve |
| Answer B Explanation | [[AnswerBExp::Incorrect. This arises from the posterior cord of the brachial plexus (C5-C8). It supplies brachioradialis, extensor muscles of the wrist and fingers, supinators, and triceps. It also sends cutaneous innervations to dorsal apect of the arm, hand and thumb. Damage to the radial nerve causes wrist drop]] |
| Answer C | AnswerC::Median nerve |
| Answer C Explanation | [[AnswerCExp::Incorrect. This arises from the medial and lateral cords of the brachial plexus (C5-C8, T1). It provides motor innervations to muscles in the forearm and hand, and cutaneous innervations in the hand. Injury to this nerve results into a combination of signs collectively known as the Ape Hand deformity.]] |
| Answer D | AnswerD::Axillary nerve |
| Answer D Explanation | [[AnswerDExp::Incorrect. It arise from the posterior cord of the brachial plexus. It supplies two muscles, deltoid (a muscle of the shoulder), and teres minor (one of the rotator cuff muscles). Injury causes loss of sensation over the deltoid muscle, and loss of shoulder abduction.]] |
| Answer E | AnswerE::Musculocutaneous nerve |
| Answer E Explanation | AnswerEExp::Incorrect. Arises from the lateral cord of the brachial plexus (C5-C7). It supplies motor innervations to coracobrachialis, biceps brachii, brachialis muscles, and cutaneous innervations to the lateral part of the forearm. |
| Right Answer | RightAnswer::A |
| Explanation | [[Explanation::The ulnar nerve arises from the medial cord of the brachial plexus (C8, T1). It runs from the shoulder to the hand, passing behind the medial epicondyle of the humerus, where it is exposed and subject to injuries. The ulnar nerve innervates muscles in the forearm and hand, and also provides cutaneous branches to the fourth and fifth digits of the hand. Motor functions include: wrist flexion, abduction and adduction of fingers, adduction of the thumb, and extension of the fourth and fifth fingers. Signs of ulnar nerve damage include radial deviation of wrist on flexion and claw hand (inability to straighten the fingers). Educational Objective: |
| Approved | Approved::No |
| Keyword | WBRKeyword::Ulnar nerve, WBRKeyword::Brachial plexus |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |