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 the 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 innervation to muscles in the forearm and hand, and sensory innervation to the lateral aspect of the palm. Injury to the median nerve may present with loss of abduction, opposition, and flexion of the thumb.]]
Answer D	AnswerD::Axillary nerve
Answer D Explanation	[[AnswerDExp::The axillary nerve arises from the posterior cord of the brachial plexus (C5-C6) and innervates the deltoids and teres minor. Injury causes impaired sensation of the deltoid and lateral arm and loss of arm abduction at shoulder.]]
Answer E	AnswerE::Musculocutaneous nerve
Answer E Explanation	[[AnswerEExp::The musculocutaneous nerve arises from the lateral cord of the brachial plexus (C5-C7). The musculocutaneous nerve innervates the coracobrachialis, biceps brachii, brachialis muscles, and the lateral aspect 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::Yes
Keyword	WBRKeyword::Ulnar nerve, WBRKeyword::Brachial plexus
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::