Claw hand and injury in Guyon's canal involve which nerve?

• A. Ulnar nerve
• B. Median nerve
• C. Radial nerve
• D. Musculocutaneous nerve

Answer: (A)

Claw hand from a wrist-level ulnar nerve problem arises because the intrinsic hand muscles lose their motor input. Guyon's canal is the ulnar nerve tunnel at the wrist, where the nerve splits into a superficial sensory branch and a deep motor branch. When the motor fibers that go to the intrinsic hand muscles—interossei, the medial two lumbricals, and the adductor pollicis—are affected, the delicate balance that allows flexion at the MCP joints and extension at the IP joints is lost. Interossei normally flex the metacarpophalangeal joints and extend the finger IP joints; without them, the extensor digitorum can overly extend the MCPs while the flexors pull the IP joints into flexion, producing a claw-like posture, especially in the ring and little fingers. Loss of adductor pollicis also reduces thumb adduction, further compromising grip and precision. Sensation may be reduced in the ulnar-nerve distribution on the palmar and dorsal aspects of the ulnar one-and-a-half digits. This combination of motor and sensory changes points to injury of the ulnar nerve at Guyon's canal.