Flexor retinaculum of the hand

The flexor retinaculum (transverse carpal ligament, or anterior annular ligament) is a strong, fibrous band, which arches over the carpus, converting the deep groove on the front of the carpal bones into a tunnel, the carpal tunnel, through which the Flexor tendons of the digits and the median nerve pass.

It is attached, medially, to the pisiform and the hamulus of the hamate bone; laterally, to the tubercle of the scaphoid, and to the medial part of the volar surface and the ridge of the trapezium.

It is continuous, above, with the volar carpal ligament; and below, with the palmar aponeurosis. It is crossed by the ulnar vessels and nerve, and the cutaneous branches of the median and ulnar nerves.

At its lateral end is the tendon of the Flexor carpi radialis, which lies in the groove on the greater multangular between the attachments of the ligament to the bone.

On its volar surface the tendons of the Palmaris longus and Flexor carpi ulnaris are partly inserted; below, it gives origin to the short muscles of the thumb and little finger.