Why does an ulnar nerve lesion at the wrist produce MORE severe clawing of the ring and little fingers than an ulnar nerve lesion at the elbow?

• A Flexor digitorum profundus remains functional in the distal lesion, preserving the deforming flexion force ✓
• B Lumbricals are denervated only in the distal lesion
• C The digital branches carry more sensory fibres when injured proximally
• D Extensor expansion dysfunction occurs only in the distal lesion

Explanation

This is the ulnar paradox. Clawing requires loss of interossei and lumbricals combined with a functioning long flexor. In a distal lesion, flexor digitorum profundus to the ring and little fingers is spared, so its flexion pull acts unopposed on the interphalangeal joints. In a proximal lesion, FDP is paralysed as well, so the fingers cannot be actively flexed into the claw position, making the deformity look less severe despite greater total weakness.

Reference: Moore's Clinically Oriented Anatomy, 9th ed.

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Written and medically reviewed by the StethoPrep medical team.