WBR0496
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| Author | [[PageAuthor::William J Gibson (Reviewed by Serge Korjian and Yazan Daaboul, M.D.)]] |
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| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Anatomy |
| Sub Category | SubCategory::Musculoskeletal/Rheumatology, SubCategory::General Principles |
| Prompt | [[Prompt::A 30-year-old man is brought to the emergency department for right arm trauma following an injury during a lacrosse game. The patient reports 9/10 pain for which he took ibuprofen en route to the hospital. An X-ray of the right arm is shown below. Which of the following is most likely to be impaired in this patient?
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| Answer A | AnswerA::Thumb adduction |
| Answer A Explanation | AnswerAExp::The ulnar nerve is responsible for adduction of the thumb. |
| Answer B | AnswerB::Forearm pronation |
| Answer B Explanation | AnswerBExp::The radial nerve is responsible for innervating the supinators of the forearm. |
| Answer C | AnswerC::Arm abduction beyond 15 degrees |
| Answer C Explanation | AnswerCExp::The deltoid muscle is responsible for arm abduction beyond 15 degrees. The deltoid is innervated by the axillary nerve, which is typically affected by fractures at the surgical neck of the humerus. |
| Answer D | AnswerD::Wrist extension |
| Answer D Explanation | AnswerDExp::The radial nerve is responsible for innervating the extensors of the wrist. The radial nerve is damaged by midshaft humeral fractures, such as the one pictured above. |
| Answer E | AnswerE::Wrist flexion |
| Answer E Explanation | AnswerEExp::The median and ulnar nerves are responsible for wrist flexion. |
| Right Answer | RightAnswer::D |
| Explanation | [[Explanation::Midshaft humeral fractures usually result from a direct blow injury to the humerus. They are usually induced by high velocity trauma among young adults and low velocity trauma most likely from falls among older women. Classical risk factors associated with midshaft humeral fractures include advanced age, trauma, and osteoporosis. Signs and symptoms include pain accompanied by edema and possibly subcutaneous bleeding. Pain may be either localized to the mid-arm region or referred (proximally towards the shoulder or distally towards the elbow). The above image demonstrates a classical midshaft fracture of the humerus. Physical examination is often remarkable for tenderness and crepitus at the site of the fracture. Neurovascular examination following fractures is very significant to ensure adequate blood supply and nerve innervation to all surrounding tissues. Patients with midshaft humeral fractures often present with radial nerve injury. The radial nerve is responsible for the innervation of the extensors of the wrist. Educational Objective: The radial nerve is responsible for innervating the extensors of the wrist. The radial nerve is damaged by midshaft fractures of the humerus such as the one pictured above. |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Arm, WBRKeyword::Humerus, WBRKeyword::Fracture, WBRKeyword::Nerve, WBRKeyword::Radial Nerve, WBRKeyword::Brachial, WBRKeyword::Brachial plexus, WBRKeyword::Midshaft |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |
