WBR0489

Author	[[PageAuthor::William J Gibson, (Reviewed by Alison Leibowitz)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Anatomy
Sub Category	SubCategory::Musculoskeletal/Rheumatology, SubCategory::General Principles
Prompt	[[Prompt::An 8-year-old male is brought to the emergency room 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 of his right arm and is unable to extend his wrist. His right hand in clenched, in a “claw hand” configuration similar to the image displayed below. Upon physical examination, the child has significant swelling on the left side of his body and scratches from the fall, but no evidence of skeletal fractures. Which of the following nerves is most likely damaged in this patient? ]]
Answer A	AnswerA::Median Nerve
Answer A Explanation	[[AnswerAExp::The median nerve is not typically damaged in Klumpke’s palsy. However, patients with Klumpke's palsy will frequently exhibit weakness of the thenar eminence, 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’s palsy. The radial nerve can be injured in Erb’s palsy, a condition in which the superior trunk of the brachial plexus is injured. Erb’s palsy causes a “waiter’s tip” appearance of the arm and hand.]]
Answer C	AnswerC::Ulnar Nerve
Answer C Explanation	[[AnswerCExp::While the injured C8-T1 nerve roots give rise to the ulnar nerve, the ulnar nerve itself is not damaged in Klumpke’s 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
Answer D Explanation	AnswerDExp::These are the nerve roots injured in Erb’s palsy.
Answer E	AnswerE::C8-T1
Answer E Explanation	AnswerEExp::Klumpke’s palsy results from the injury of the C8-T1 nerve roots.
Right Answer	RightAnswer::E
Explanation	[[Explanation::The patient in this vignette has Klumpke’s palsy, a condition caused by damage to the inferior trunk of the brachial plexus (nerve roots C8-T1). Klumpke’s 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 the characteristic “Klumpke’s (total) claw” hand appearance due to loss of lumbrical function. 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. Educational Objective: The inferior trunk of the brachial plexus is injured in Klumpke’s palsy. References: First Aid 2012 page 408, 410]]
Approved	Approved::Yes
Keyword	WBRKeyword::Klumpke Palsy, WBRKeyword::Arm, WBRKeyword::Nerve, WBRKeyword::Paralysis, WBRKeyword::Muscle, WBRKeyword::Hand, WBRKeyword::nervous system, WBRKeyword::neurology, WBRKeyword::nerve roots
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Order in Linked Questions	LinkedOrder::