Median Nerve Injury: Loss of Thumb Opposition
The patient will lose the ability to oppose the thumb (answer D), as the nerve immediately lateral to the flexor digitorum superficialis tendon at the wrist is the median nerve, which innervates the thenar muscles responsible for thumb opposition.
Anatomical Basis
The median nerve runs immediately lateral to the flexor digitorum superficialis (FDS) tendon in the carpal tunnel at the wrist level. This anatomical relationship makes it vulnerable to laceration injuries in this region.
Key Functions Lost with Median Nerve Injury
Thumb opposition is the primary function lost because the median nerve innervates the thenar muscles (opponens pollicis, abductor pollicis brevis, and superficial head of flexor pollicis brevis), which are essential for this complex movement 1, 2
The inability to oppose the thumb results in severe functional impairment, as opposition is critical for pinch grip and most hand functions 3
Why Other Options Are Incorrect
Abduction of the Second Digit (Option A)
- The second digit (index finger) abduction is controlled by the first dorsal interosseous muscle, which is innervated by the ulnar nerve, not the median nerve
- This function would remain intact with isolated median nerve injury
Adduction of the Second Digit (Option B)
- Index finger adduction is performed by the palmar interossei and second palmar interosseous, which are also innervated by the ulnar nerve
- This function would be preserved
Flexion at the Interphalangeal Joint of the Thumb (Option C)
- Thumb IP joint flexion is performed by flexor pollicis longus, which receives its innervation from the anterior interosseous nerve (a branch of the median nerve) in the proximal forearm, well above the wrist
- Since the injury is at the wrist level, the motor branch to FPL (given off proximally) would remain intact, preserving this function
Clinical Management Considerations
Immediate surgical exploration is indicated for nerve lacerations with loss of function 4
MRI with dedicated neurography sequences can improve visualization of injured nerves in cases of suspected traumatic nerve injury, though clinical examination typically suffices for complete lacerations 4
Tendon transfer procedures (such as FDS opponensplasty) can restore thumb opposition if nerve repair fails or is not possible, with excellent results reported in 90% of cases 5, 2
The timing of nerve repair is critical for optimal outcomes, with early intervention (within days to weeks) associated with superior functional recovery 6