The transverse carpal ligament (TCL) is a thick, dense band of connective tissue spanning the width of the wrist. This structure creates a protective enclosure for important structures passing into the hand. The TCL is central to the condition known as Carpal Tunnel Syndrome, a common nerve compression disorder.
Location and Defining the Carpal Tunnel
The transverse carpal ligament is situated on the palm side of the wrist, acting as the roof of the narrow passageway called the carpal tunnel. The floor and sides of this tunnel are formed by the deep, arched arrangement of the eight carpal bones. The TCL converts this bony arch into a complete, enclosed tunnel.
Anatomists often refer to the TCL as the flexor retinaculum because it retains the flexor tendons. On the radial side, closer to the thumb, the ligament attaches to the tubercle of the scaphoid bone and the ridge of the trapezium. It extends across the wrist to the ulnar side, attaching to the pisiform bone and the hook of the hamate. This fibrous band is strong, with fibers oriented primarily in a transverse direction.
Mechanical Role: Protection and Containment
The primary function of the TCL is to contain and secure the nine long flexor tendons and the median nerve as they enter the hand from the forearm. Without this restraining band, the tendons would lift away from the wrist bones, a phenomenon called “bowstringing,” whenever the fingers or wrist are flexed. The ligament acts like a pulley system, ensuring the flexor tendons remain close to the bones.
This close proximity allows the forearm muscles to exert maximum force and efficiency when gripping or moving the fingers. The TCL also serves as an anchoring point for some of the small muscles in the hand, specifically those at the base of the thumb and little finger. By providing a fixed point for these muscles, the ligament contributes to hand strength and stability during movement.
The Transverse Carpal Ligament’s Role in Carpal Tunnel Syndrome
The strength and rigidity that make the transverse carpal ligament an effective containment structure also contribute to a common clinical problem. The carpal tunnel is a fixed-volume space, and the TCL’s inelastic nature prevents the tunnel from expanding outward. This lack of flexibility becomes problematic when swelling or inflammation occurs within the tunnel.
Any internal increase in volume, such as from inflamed tendon sheaths or fluid retention, causes pressure to build up against the unyielding TCL roof. This elevated pressure compresses the median nerve, which shares the confined space with the tendons. This nerve compression defines Carpal Tunnel Syndrome, leading to symptoms like numbness, tingling, and pain in the thumb, index, middle, and half of the ring finger.
To relieve this pressure, the surgical procedure known as carpal tunnel release is performed. This operation involves surgically cutting, or transecting, the transverse carpal ligament. Dividing the ligament immediately releases the restrictive roof of the tunnel, providing more room for the median nerve and the tendons.
The surgical division of the TCL allows the carpal arch to widen, increasing the cross-sectional area of the tunnel. While the ligament does not completely disappear, it eventually heals and grows back in a lengthened position, maintaining the enlarged space. This procedure addresses the root cause of the nerve compression by providing relief for the median nerve.