WBR0448
| Author | [[PageAuthor::Rim Halaby, M.D. [1]]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Anatomy |
| Sub Category | SubCategory::Musculoskeletal/Rheumatology |
| Prompt | [[Prompt::A 35 year old male patient who sustained a recent trauma presents to the physician’s office with flattening of the shoulder muscle. On physical examination, the patient is unable to abduct his shoulder. Which of the following traumatic injuries is most likely to be responsible for the patient’s findings?]] |
| Answer A | AnswerA::Fracture at the surgical neck of the humerus |
| Answer A Explanation | AnswerAExp::Fracture at the surgical neck of the humerus most likely injures the axillary nerve that innervates the deltoid muscle. |
| Answer B | AnswerB::Fracture at the midshaft of the humerus |
| Answer B Explanation | AnswerBExp::Fracture at the midshaft of the humerus most likely injures the radial nerve (C5-C8) that innervates the extensors of the hand and provides sensory innervations to the posterior arm and dorsal hand and thumb. |
| Answer C | AnswerC::Compression of the axilla by crutches |
| Answer C Explanation | AnswerCExp::Compression of the axilla by crutches also injures the radial nerve. |
| Answer D | AnswerD::Fracture of the supracondylar humerus |
| Answer D Explanation | [[AnswerDExp::Fracture of the supracondylar humerus injures the median nerve (C5-C8 and T1). The median nerve injury manifests as inability to oppose the thumb causing an “ape hand” appearance, and 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::Fracture of the medial epicondyle of the humerus most likely injures the ulnar nerve (C8 and T1). In ulnar nerve injury, the patient will not be able to flex his medial fingers or flex his wrist. The patient will also 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 passes with the posterior circumflex humeral artery and vein in the quadrangular space in the arm.
Educational Objective:
Fracture at the surgical neck of the humerus most likely injures the axillary nerve that innervates the deltoid muscle. |
| Approved | Approved::No |
| Keyword | WBRKeyword::Deltoid, WBRKeyword::axillary, WBRKeyword::nerve, WBRKeyword::fracture, WBRKeyword::abduct, WBRKeyword::shoulder |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |