Transverse carpal ligament (TCL)

The transverse carpal ligament (TCL), also known as the flexor retinaculum of the hand, is a thick band of connective tissue that forms the volar roof of the carpal tunnel, spanning from the scaphoid and trapezium radially to the pisiform and hamate ulnarly. It provides structural stability to the carpal arch, constrains the median nerve and nine flexor tendons within the fibro-osseous tunnel, and serves as a partial origin for thenar muscles including the abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis, enabling thumb movements like abduction, flexion, and opposition. The TCL's fibers are predominantly transverse, with varying thickness (mean 2.1 mm, thickest distally ulnarly and proximally radially), and it contributes to pulley-like motion for flexor tendons while preventing bowstringing. In carpal tunnel syndrome (CTS), TCL thickening or pathologic changes compress the median nerve, leading to neuropathy symptoms. Surgical release of the TCL remains the primary treatment for CTS, expanding tunnel volume but risking reduced carpal stability, altered tendon excursion, diminished grip strength, and long-term thenar muscle weakening. Detailed anatomical knowledge of its insertion sites and fiber orientation guides safer endoscopic or limited-incision releases and informs potential non-surgical approaches.

Other names

Flexor retinaculum (of the hand)Flexor carpi retinaculum