WBR0503

Author	[[PageAuthor::Ayokunle Olubaniyi, M.B,B.S [1] (Reviewed by Alison Leibowitz) (Reviewed by Serge Korjian)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Anatomy
Sub Category	SubCategory::Musculoskeletal/Rheumatology, SubCategory::General Principles
Prompt	[[Prompt::A 14-year-old girl is brought to the emergency department (ED) by her school nurse. The nurse explains that the girl tripped during a soccer game, breaking her fall with her left elbow. On physical examination, the physician notices weakness in wrist flexion as well as loss of sensation over the hypothenar eminence. The physician orders an X-ray for further evaluation (shown below). Which of the following nerves is most likely to be involved? ]]
Answer A	AnswerA::Ulnar nerve
Answer A Explanation	[[AnswerAExp::Damage to the ulnar nerve following medial epicondylar fracture can result in the loss of wrist flexion as well as loss of sensation over the hypothenar eminence.]]
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 with 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 descends posteromedially to the humerus in the arm, then passes behind the medial epicondyle of the humerus where it may be exposed to traumatic injuries. The patient in this scenario is presenting with a fracture of the medial epicondyle with clinically evident injury to her ulnar nerve. The ulnar nerve innervates muscles in the forearm and hand, and also provides cutaneous branches to the fourth and fifth digits. Motor functions associated with the ulnar nerve include wrist flexion (flexor carpi ulnaris and part of the flexor digitorum profundus), abduction and adduction of fingers (dorsal and palmar interossei), adduction of the thumb (adductor pollicis), and extension of the fourth and fifth fingers (third and fourth lumbrical muscles). Signs of ulnar nerve damage include radial deviation of wrist on flexion and inability to straighten the medial fingers (partial claw hand). Educational Objective: Damage to the ulnar nerve following medial epicondylar fracture can result in the loss of wrist flexion and loss of sensation over the hypothenar eminence. References: Image courtesy of Dr. Henry Knipe. Radiopaedia (original file here). Creative Commons BY-SA-NC First Aid 2014 page 415]]
Approved	Approved::Yes
Keyword	WBRKeyword::Ulnar nerve, WBRKeyword::Brachial plexus, WBRKeyword::Medial epicondyle fracture, WBRKeyword::Medial epicondyle
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::