WBR0503

Author	[[PageAuthor::Ayokunle Olubaniyi, M.B,B.S [1] (Reviewed by Alison Leibowitz)]]
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. While playing with her friends, the girl fell, breaking the fall with her outstretched left hand. Upon examination, you observe that there is a transient loss of wrist flexion as well as loss of sensation over the hypothenar eminence. An X-ray of the left hand revealed no fractures. Which of the following nerves is most likely damaged?]]
Answer A	AnswerA::Ulnar nerve
Answer A Explanation	[[AnswerAExp::Damage to the ulnar nerve can result in the loss of wrist flexion, adduction and abduction of the fingers, and extension of the thumb.]]
Answer B	AnswerB::Radial nerve
Answer B Explanation	[[AnswerBExp::The radial nerve arises from the posterior cord of the brachial plexus (C5-T1). 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 presents in wrist drop.]]
Answer C	AnswerC::Median nerve
Answer C Explanation	[[AnswerCExp::The median nerve arises from the medial and lateral cords of the brachial plexus (C5-T1). It provides motor innervations to muscles in the forearm and hand, and cutaneous innervations in the hand. Injury to the median nerve presents in abduction, opposition, and flexion of the thumb, but does not result in loss of sensation.]]
Answer D	AnswerD::Axillary nerve
Answer D Explanation	[[AnswerDExp::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::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 fingers. Motor functions associated with the ulnar nerve are 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 inability to straighten the fingers (claw hand). Educational Objective: References: ]]
Approved	Approved::No
Keyword	WBRKeyword::Ulnar nerve, WBRKeyword::Brachial plexus
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::