Kaplan USMLE Step 1: Suicide attempt risks nerve damage to hand

If you’re preparing for the United States Medical Licensing Examination® (USMLE®) Step 1 exam, you might want to know which questions are most often missed by test-prep takers. Check out this example from Kaplan Medical, and read an expert explanation of the answer. Also check out all posts in this series.

A 15-year-old girl is brought to the emergency department because of attempted suicide following a fight with her parents. The girl is markedly distressed and has sustained severe blood loss. IV fluids are started to resuscitate the patient, and her blood pressure and heart rate respond appropriately. The patient is transferred to the in-patient psychiatric ward for close monitoring and a more comprehensive workup. Physical examination is notable for multiple deep cuts on the wrist and severed flexor carpi radialis and palmaris longus tendons. The nerve at greatest risk from this injury most likely arises from which of the following part(s) of the brachial plexus?

A. Lateral and medial cords 

B. Lateral and posterior cords 

C. Lateral cord only 

D. Posterior and medial cords 

E. Posterior cord only

The correct answer is A.

Kaplan Medical explains why

The lateral and medial cords of the brachial plexus give rise to the median nerve. This nerve is at risk from self-induced wrist cuts as this nerve travels between the palmaris longus and flexor carpi radialis tendons.

Why the other answers are wrong

Choice B. The lateral cord contributes to the median nerve, but the posterior cord does not. The posterior cord gives rise to the axillary and radial nerves.