WBR0489
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| Author | [[PageAuthor::William J Gibson (Reviewed by Yazan Daaboul, M.D. and Alison Leibowitz [1])]] |
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| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Anatomy |
| Sub Category | SubCategory::Musculoskeletal/Rheumatology, SubCategory::General Principles |
| Prompt | [[Prompt::An 24-year-old man is brought to the emergency department after falling from a tree. He was able to break his fall by grabbing onto a branch with his right hand during his descent. He reports severe pain in his right arm and is unable to extend his right wrist (shown below). On physical examination, the patient has several scratches from the fall but no evidence of skeletal fractures. Which of the following nerves is most likely injured in this patient?
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| Answer A | AnswerA::Median nerve |
| Answer A Explanation | [[AnswerAExp::The median nerve is not typically damaged in Klumpke palsy. However, patients with Klumpke palsy will frequently exhibit weakness of the thenar eminence, which is innervated by the median nerve. These muscles are innervated by the nerves passing through the median nerve from the C8-T1 nerve roots.]] |
| Answer B | AnswerB::Radial nerve |
| Answer B Explanation | AnswerBExp::The radial nerve is not typically damaged in Klumpke palsy. The radial nerve can be injured in Erb palsy, where the superior trunk of the brachial plexus is injured. Erb palsy causes a “waiter’s tip” appearance of the arm and hand. |
| Answer C | AnswerC::Ulnar nerve |
| Answer C Explanation | [[AnswerCExp::While the ulnar nerve originates from the C8-T1 nerve roots, the ulnar nerve itself is not damaged in Klumpke palsy. A lesion of the ulnar nerve can be caused by a fracture of the medial epicondyle of the humerus, giving rise to the “ulnar claw”. In this condition, the fourth and fifth digits flex when attempting to open the hand.]] |
| Answer D | AnswerD::C5-C6 nerve roots |
| Answer D Explanation | AnswerDExp::C5 and C6 nerve roots (and occasionally C7 nerve root) are damaged in Erb palsy, which is characterized by failure to abduct, laterally rotate, supinate, and flex the arm. |
| Answer E | AnswerE::C8-T1 |
| Answer E Explanation | AnswerEExp::Klumpke palsy results from an injury of the C8-T1 nerve roots. |
| Right Answer | RightAnswer::E |
| Explanation | [[Explanation::Klumpke palsy is caused by damage to the inferior trunk of the brachial plexus (nerve roots C8-T1). Klumpke palsy is often caused by forceful, excessive abduction of the arm. This can occur during an attempt to catch oneself during a fall or when an infant’s arm is abducted during a vaginal birth. Individuals will often present with a characteristic Klumpke (total) "claw hand" appearance due to loss of lumbrical function, as displayed in the vignette. The ulnar nerve supplies the third and fourth lumbricals (the most ulnar two digits) as well as the flexors of the wrist. The C8-T1 fibers of the median nerve supply the first and second lumbricals.
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| Approved | Approved::Yes |
| Keyword | WBRKeyword::Klumpke palsy, WBRKeyword::Nerve, WBRKeyword::Paralysis, WBRKeyword::Nerve roots, WBRKeyword::Trauma, WBRKeyword::Fall, WBRKeyword::Claw hand, WBRKeyword::Brachial plexus |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |
