Why does a proximal ulnar nerve lesion at the elbow produce less obvious clawing than a distal lesion at the wrist?

• A Denervation of FDP removes the deforming force on the IP joints ✓
• B Proximal lesions spare FDP to the ring and little fingers
• C Proximal lesions allow earlier reinnervation of the interossei
• D The lumbricals are spared because they have a dual innervation

Explanation

This is the ulnar paradox. The claw deformity requires two components: intrinsic muscle paralysis allowing MCP hyperextension, and continued flexor digitorum profundus pull flexing the IP joints. In a high ulnar lesion, FDP to the ring and little fingers is paralysed along with the intrinsics, so the unopposed deforming flexion force is absent and the claw appears flatter. Option D is false because the ulnar two lumbricals are purely ulnar innervated.

Reference: Campbell's Operative Orthopaedics, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.