Retinaculum

A retinaculum is a band or thickening of deep fascia that acts as a restraining structure across a joint to hold tendons in their proper path as they cross the joint. By functioning like a pulley, retinacula prevent tendon bowstringing during motion and help distribute mechanical forces through the limb.

Retinacula are encountered around several joints. In the wrist, the flexor retinaculum, also known as the transverse carpal ligament, spans the carpal bones to form the roof of the carpal tunnel, connecting the scaphoid and trapezium laterally with the pisiform and hook of the hamate medially. The extensor retinaculum of the wrist holds the extensor tendons on the dorsal aspect with distinct superior and inferior portions. Around the knee, the medial and lateral patellar retinacula are expansions of fascia that stabilize the patella as it tracks within the trochlear groove. In the ankle and foot, extensor retinacula hold the tendons of the anterior compartment in place as they cross the ankle and the dorsum of the foot, with organized proximal and distal bands.

Clinical significance includes loss of normal tendon alignment when retinacular structures are injured or lax, which can lead to tendon bowstringing, impingement, or maltracking. The carpal tunnel is formed in part by the flexor retinaculum, and carpal tunnel syndrome results from compression within this space. Patellar retinacular dysfunction can contribute to patellofemoral pain or instability.

Etymology: retinaculum derives from Latin retinere, meaning to hold back.