Why does a low ulnar nerve lesion at the wrist produce more obvious clawing than a high lesion at the elbow?

• A The flexor digitorum profundus to ring and little fingers is paralysed in a low lesion
• B The lumbricals are hypertrophied in a high lesion
• C The flexor digitorum profundus to ring and little fingers remains active in a low lesion, adding to the deformity ✓
• D The extensor digitorum is denervated in a low lesion

Explanation

This is the ulnar paradox. In a low lesion, the ulnar half of flexor digitorum profundus remains innervated, so its unopposed action flexes the interphalangeal joints and exaggerates the claw caused by lost interossei and lumbricals. In a high lesion, that same profundus is paralysed, removing the IP joint flexion component and making the claw less apparent despite a more proximal injury. Extensor digitorum is radial nerve supplied and unaffected in either lesion.

Reference: Bailey and Love's Short Practice of Surgery, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.