Median Nerve Laceration at the Wrist: Lost Function
Opposition of the thumb will no longer be possible following laceration of the median nerve immediately lateral to the flexor digitorum superficialis tendon at the wrist. 1
Anatomical Basis
The median nerve at the wrist level innervates the thenar muscles (abductor pollicis brevis, opponens pollicis, and superficial head of flexor pollicis brevis), which are essential for thumb opposition. 1 Opposition involves three coordinated movements: abduction, flexion, and pronation of the thumb—all of which require intact thenar muscle function. 1
Why Other Options Are Incorrect
Abduction of the second digit (index finger): This is controlled by the first dorsal interosseous muscle, which receives innervation from the ulnar nerve, not the median nerve. 2
Adduction of the second digit: This is also performed by interosseous muscles innervated by the ulnar nerve. 2
Flexion at the interphalangeal joint of the thumb: This action is performed by the flexor pollicis longus, which is innervated by the anterior interosseous nerve (a branch of the median nerve) that originates proximal to the wrist in the forearm. 2 A laceration at the wrist level would not affect this muscle's function since its nerve supply branches off well above the injury site. 2
Clinical Significance
Thumb opposition loss represents the most functionally devastating consequence of median nerve injury at the wrist level. 1 While patients with high median nerve injuries (above the elbow) demonstrate preserved thumb function scoring above 5 on the Kapandji scale due to compensatory mechanisms, distal median nerve injuries at the wrist directly compromise thenar muscle function without such compensation. 2
Grasp and pinch strength are significantly reduced following median nerve injury, averaging 43% and 36% of normal limb strength respectively, primarily due to loss of thenar muscle function. 2 This functional deficit warrants surgical reconstruction in most cases. 2
Management Considerations
Wrist splinting in neutral position minimizes pressure in the carpal tunnel and can help prevent further compression during the healing phase. 3 For complete nerve lacerations, microsurgical repair should be performed soon after injury to optimize functional outcomes. 4 Despite advances in microsurgical techniques, many patients do not achieve ideal outcomes and may require subsequent tendon transfer procedures to restore opposition if nerve regeneration is inadequate. 1, 4