The flexor retinaculum (transverse carpal ligament, or anterior annular ligament) is a strong, fibrous band of the hand that arches over the carpal bones. By covering the carpal bones if forms the carpal tunnel, through which the median nerve and tendons of muscles which flex the hand pass.
On the ulnar side, the flexor retinaculum attaches to the pisiform bone and the hook of the hamate bone. On the radial side, it attaches to the tubercle of the scaphoid bone, and to the medial part of the palmar surface and the ridge of the trapezium bone.
The flexor retinaculum is continuous with the palmar carpal ligament, and deeper with the palmar aponeurosis. The ulnar artery and ulnar nerve, and the cutaneous branches of the median and ulnar nerves, pass on top of the flexor retinaculum.
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 palmar surface the tendons of the palmaris longus and flexor carpi ulnaris are partly attached; below, the short muscles of the thumb and little finger originate from the flexor retinaculum.
Ten fresh-frozen cadaver wrists were used to digitize three-dimensionally. The attachments of each ligament were represented in a model combining CT surfaces overlaid by a digitized 3-D surface, and were also visually depicted with a different color for each on 3-D images of the bones.
The flexor retinaculum was found to be composed of two or three discrete ligaments. Both the trapezium-hook of hamate ligament and the trapezium-pisiform ligament were identified in all ten specimens. The scaphoid-pisiform ligament was found in only two of the ten specimens. The average areas of the attachments of the TCL were 42.7 mm(2) on the trapezium, 30.0 mm(2) on the hook of hamate, 21.6 mm(2) on the pisiform, and 12.7 mm(2) on the scaphoid.
The anatomic 3-D attachment sites of the TCL were visually shown qualitatively, and their areas quantified. This 3-D information offers further knowledge and understanding of the anatomy and biomechanics of the TCL. It could also help in the accurate assessment of radiographic images and treatment of various wrist injuries and diseases when performing such procedures as carpal tunnel release, Guyon's canal release, trapeziectomy, hook of hamate excision, or arthroscopy 1).