A patient has a complete ulnar nerve transection at the level of the mid humerus. Compared with an ulnar nerve lesion at the wrist, the clawing of the ring and little fingers is noticeably less severe. What is the reason?

• A The ulnar paradox results from loss of the lumbricals alone
• B The intrinsic muscles are spared in high lesions
• C The flexor digitorum profundus to these fingers is denervated, removing the deforming force ✓
• D Median nerve crossover reinnervates the interossei in high lesions

Explanation

Clawing results from unopposed long flexor action on denervated interossei and lumbricals. In a high ulnar lesion the flexor digitorum profundus to the ring and little fingers is also paralysed, so there is no flexion force at the distal interphalangeal joint to accentuate the deformity. This apparent lesser deformity with worse overall deficit is called the ulnar paradox. Intrinsic muscles are denervated in both lesions.

Reference: Miller's Review of Orthopaedics, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.