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.
The recurrent motor branch has three anatomical variants: extraligamentous (55%, exits distal to the ligament, safest), subligamentous (31%, exits through the ligament and curves back), and transligamentous (14%, pierces through the ligament itself, highest risk). During carpal tunnel release, an incision made too radially risks this branch regardless of variant. The branch is the nerve most injured by penetrating trauma at the thenar eminence base. Denervation produces loss of thumb opposition (APB weakness) and thenar atrophy.
Division of the recurrent motor branch during carpal tunnel decompression, particularly in transligamentous variants or when incision extends too radially at the distal tunnel, produces permanent loss of thumb opposition from APB denervation, emphasising the importance of staying ulnar to the ring finger axis and identifying the nerve before dividing the retinaculum.
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