A 45-year-old man falls from a height and sustains a fracture of the shaft of the humerus at the junction of the middle and lower thirds. He is unable to extend the wrist and fingers and has numbness in the dorsal web space between the thumb and index finger. Which nerve is damaged, and at what site does it bear this vulnerability?

• A Radial nerve in the spiral groove of the humerus ✓
• B Posterior interosseous nerve at the arcade of Frohse
• C Ulnar nerve in the cubital tunnel
• D Median nerve at the pronator teres

Explanation

The radial nerve is closely related to the humerus as it winds through the spiral (radial) groove on the posterior surface at the junction of middle and lower thirds. Fractures here classically injure the radial nerve, producing wrist drop (loss of wrist and finger extension) and sensory loss over the dorsal first web space. The posterior interosseous nerve is a deeper branch and its injury spares wrist extension (ECRL is spared).

Reference: Maheshwari Essential Orthopaedics, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.