Anterior interosseous syndrome involves injury to which nerve branch and affects which movement?

Anterior interosseous syndrome involves injury to which nerve branch and affects which movement?

• A. Median nerve proper; affects pinch between thumb and index finger
• B. Ulnar nerve; affects finger abduction
• C. Radial nerve; affects wrist extension
• D. Anterior interosseous branch of the median nerve; affects pinch between thumb and index finger

Answer: (D)

An anterior interosseous syndrome is a palsy of a pure motor branch of the median nerve that supplies the deep forearm flexors. Specifically, this branch innervates flexor pollicis longus and the lateral part of flexor digitorum profundus (to the index finger), along with pronator quadratus. When this nerve branch is impaired, the patient can’t adequately flex the distal joints needed for a precise tip-to-tip pinch—thumb IP flexion and index finger DIP flexion—so they lose the ability to pinch exactly between the thumb and index finger and instead use a broader, pad-to-pad pinch. Sensation remains intact because this is a motor-only distribution. The other nerves involve different functions: the ulnar nerve affects finger abduction/adduction, the radial nerve affects wrist extension, and the median nerve proper would produce broader motor and possibly sensory deficits rather than this isolated loss of tip-to-tip pinch.

An anterior interosseous syndrome is a palsy of a pure motor branch of the median nerve that supplies the deep forearm flexors. Specifically, this branch innervates flexor pollicis longus and the lateral part of flexor digitorum profundus (to the index finger), along with pronator quadratus. When this nerve branch is impaired, the patient can’t adequately flex the distal joints needed for a precise tip-to-tip pinch—thumb IP flexion and index finger DIP flexion—so they lose the ability to pinch exactly between the thumb and index finger and instead use a broader, pad-to-pad pinch. Sensation remains intact because this is a motor-only distribution.

The other nerves involve different functions: the ulnar nerve affects finger abduction/adduction, the radial nerve affects wrist extension, and the median nerve proper would produce broader motor and possibly sensory deficits rather than this isolated loss of tip-to-tip pinch.