Tarsal sinus

The tarsal sinus (sinus tarsi) is a cone-shaped anatomical space located on the lateral aspect of the foot, between the talus and calcaneus, at the junction of the midfoot and hindfoot. It is bounded superiorly by the talus, inferiorly by the calcaneus, and laterally opens to the skin, while medially it communicates with the tarsal canal. The sinus tarsi contains fat, blood vessels, nerves, and several key ligamentous structures that contribute to subtalar joint stability and proprioception.

Within the tarsal sinus, the principal ligamentous structures are the cervical ligament (Anterior talocalcaneal ligament), which lies anteriorly and obliquely at approximately a 45-degree angle to the calcaneus, and the interosseous talocalcaneal ligament, which is located more medially and deep within the tarsal canal. The inferior extensor retinaculum (IER) inserts into the sinus tarsi via three roots (lateral, intermediate, and medial), with the medial root forming a V-shaped complex with the ITCL. The anterior capsular ligament and the tarsal canal ligament (TCL) may also be present in some specimens.

The sinus tarsi is richly innervated, containing free nerve endings and mechanoreceptors (Pacinian, Golgi, and Ruffini corpuscles), and is supplied by an arterial network formed by anastomoses of the lateral tarsal and posterior tibial arteries. A venous plexus drains the region, particularly the talus and joint capsule.