Why does a proximal ulnar nerve lesion at the elbow typically produce LESS clawing of the ring and little fingers than a distal lesion at the wrist?
- A At the elbow, denervation of the medial half of flexor digitorum profundus removes the deforming flexion force at the fingers ✓
- B At the elbow, the lumbricals are spared because they have a dual nerve supply
- C At the wrist, collateral reinnervation from the median nerve restores intrinsic muscle tone
- D At the elbow, the hypothenar muscles are spared, balancing the deformity
Correct answer: A. At the elbow, denervation of the medial half of flexor digitorum profundus removes the deforming flexion force at the fingers
Explanation
The claw results from unopposed long finger extensors acting on metacarpophalangeal joints combined with flexion at the interphalangeal joints driven by flexor digitorum profundus. With a proximal lesion, the ulnar half of flexor digitorum profundus is paralysed along with the interossei and medial lumbricals, so the interphalangeal flexion component is lost and the claw is attenuated. This inversion of expected severity is called the ulnar paradox.
Reference: Snell's Clinical Anatomy by Regions, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.