A man who walks with axillary crutches develops weakness of elbow, wrist and finger extension together with an absent triceps reflex. Where is the radial nerve compressed?

• A Spiral groove of the humerus
• B Arcade of Frohse at the proximal forearm
• C Axilla, against the shaft of the humerus ✓
• D Cubital fossa, between brachialis and brachioradialis

Explanation

Crutch palsy compresses the radial nerve high in the axilla before it gives off its branches to the long and medial heads of triceps. Involvement of all three heads with an absent triceps jerk localises the lesion proximal to the spiral groove. In a spiral groove lesion, as after a midshaft humeral fracture, triceps function and the triceps reflex are typically preserved because those branches leave the nerve before the groove, which excludes option A.

Reference: Snell's Clinical Anatomy by Regions, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.