The recurrent (thenar) motor branch of the median nerve arises from the radial side of the median nerve just distal to the transverse carpal ligament and curves back (recurs) proximally and radially to enter and supply the thenar muscles: abductor pollicis brevis, opponens pollicis, and the superficial head of flexor pollicis brevis. It is a short branch, approximately 3-4 cm long, at risk during carpal tunnel surgery.
| Origin | Median nerve at or just distal to the distal border of the flexor retinaculum |
|---|---|
| Course | Arises from the radial side of the median nerve, curves proximally and radially, and enters the thenar muscles |
| Motor |
The recurrent motor branch has three main patterns: extraligamentous (about half of hands, branching distal to the transverse carpal ligament and curving back), subligamentous (branching within the carpal tunnel and running under the ligament before emerging), and transligamentous (branching within the tunnel and piercing the ligament, the highest-risk variant). In open carpal tunnel release the incision is kept in line with the ring finger axis, ulnar to the branch; the transligamentous variant is also at risk with blind or endoscopic division of the ligament. Penetrating wounds at the base of the thenar eminence often injure it. Denervation causes loss of thumb opposition, and visible thenar wasting is a sign of advanced median nerve compression.
Division of the recurrent motor branch, especially a transligamentous variant or with an incision placed too radially, causes permanent loss of thumb opposition from abductor pollicis brevis and opponens denervation.
Long-standing compression of the median nerve in the carpal tunnel affects the motor fibres to this branch, producing thenar wasting and weak abduction of the thumb, which indicates the need for prompt decompression.
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