Two patients have complete ulnar nerve palsies, one at the level of the elbow and one at the wrist. On comparing their hands, the patient with the ELBOW lesion shows LESS obvious clawing of the ring and little fingers than the patient with the wrist lesion. What explains this observation?
- A At the elbow, denervation of flexor digitorum profundus removes the deforming force that hyperextends the MCP joints ✓
- B At the elbow, the interossei are spared because they take a proximal branch before the cubital tunnel
- C At the wrist, the lumbricals are denervated whereas at the elbow only hypothenar muscles are affected
- D Clawing requires an intact median nerve, which is more often co-injured at the elbow
Correct answer: A. At the elbow, denervation of flexor digitorum profundus removes the deforming force that hyperextends the MCP joints
Explanation
This is the ulnar paradox. Clawing results from intrinsic paralysis combined with an intact long flexor tone: flexor digitorum profundus flexes the IP joints while the unopposed extensors hyperextend the MCP joints. B high lesion at the elbow denervates the ulnar half of flexor digitorum profundus, removing this flexion deformity and reducing visible clawing despite a more proximal and extensive lesion.
Reference: Moore's Clinically Oriented Anatomy, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.