WBR0448

Author	[[PageAuthor::Rim Halaby, M.D. [1] (Reviewed by Alison Leibowitz)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Anatomy
Sub Category	SubCategory::Musculoskeletal/Rheumatology
Prompt	[[Prompt::A 35-year-old male, who sustained a recent trauma, presents to the physician’s office with flattening of the shoulder muscle. Upon physical examination, the patient is unable to abduct his shoulder. Which of the following traumatic injuries is most likely responsible for the patient’s symptoms?]]
Answer A	AnswerA::Fracture at the surgical neck of the humerus
Answer A Explanation	AnswerAExp::See explanation.
Answer B	AnswerB::Fracture at the midshaft of the humerus
Answer B Explanation	[[AnswerBExp::A fracture at the midshaft of the humerus most likely injures the radial nerve (C5-C8) which innervates the extensors of the hand and provides sensory innervations to the posterior arm, dorsal hand, and thumb.]]
Answer C	AnswerC::Compression of the axilla by crutches
Answer C Explanation	[[AnswerCExp::Compression of the axilla by crutches also most likely injures the radial nerve.]]
Answer D	AnswerD::Fracture of the supracondylar humerus
Answer D Explanation	[[AnswerDExp::A fracture of the supracondylar humerus most likely injures the median nerve (C5-C8 and T1). A median nerve injury manifests with the inability to oppose the thumb, causing an “ape hand” appearance, and the loss of sensation over the dorsal and palmar aspects of the thenar eminence and the lateral 3 and ½ fingers.]]
Answer E	AnswerE::Fracture of medial epicondyle of the humerus
Answer E Explanation	[[AnswerEExp::A fracture of the medial epicondyle of the humerus most likely injures the ulnar nerve (C8 and T1). In ulnar nerve injuries, patients frequently will be unable to flex their medial fingers and wrists and lose sensation over the hypothenar eminence and the median 1 ½ fingers.]]
Right Answer	RightAnswer::A
Explanation	[[Explanation::A fractured surgical neck of the humerus is most likely to injure the axillary nerve (C5-C6) that innervates the deltoid muscle. The deltoid muscle is responsible for shoulder abduction, which is injured in this patient. The axillary nerve is also called the circumflex nerve, because it is grouped with the posterior circumflex humeral artery and vein, in the quadrangular space in the arm. Educational Objective: A fractured surgical neck of the humerus is most likely to injure the axillary nerve (C5-C6) that innervates the deltoid muscle. References: First Aid 2014 page 411]]
Approved	Approved::Yes
Keyword	WBRKeyword::Deltoid, WBRKeyword::axillary nerve, WBRKeyword::fracture, WBRKeyword::abduct, WBRKeyword::nervous system, WBRKeyword::abduction, WBRKeyword::innervation
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