A 22-year-old motorcyclist has a fracture of the shaft of the humerus at the junction of the middle and lower thirds. Which nerve is most commonly injured at this site and what functional deficit would be expected?
- A Ulnar nerve; loss of ring and little finger flexion
- B Median nerve; inability to oppose thumb
- C Radial nerve; wrist drop and loss of thumb extension ✓
- D Musculocutaneous nerve; loss of elbow flexion
Correct answer: C. Radial nerve; wrist drop and loss of thumb extension
Explanation
The radial nerve winds around the posterior aspect of the humerus in the spiral groove and is tethered as it pierces the lateral intermuscular septum at the junction of the middle and lower thirds of the humerus, making it highly vulnerable at this site. Injury causes wrist drop (loss of wrist and finger extension) due to paralysis of extensor carpi radialis, extensor digitorum, and extensor pollicis. Sensation is lost over the dorsum of the first web space.
Reference: Maheshwari Essential Orthopaedics, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.