The tarsal sinus (or sinus tarsi) is a cylindrical cavity located between the talus and calcaneus on the lateral aspect of the foot. MRI is the investigation of choice for evaluating the tarsal sinus structures.
The tarsal sinus is situated on the lateral side of the foot; distal and slightly anterior to the lateral malleolus. It is a space bordered by the neck of the talus and anterosuperior aspect of the calcaneus. The tarsal sinus opens medially, posterior to the sustentaculum tali of the calcaneus, as a funnel-shaped tarsal canal. The sinus tarsi separates the anterior subtalar joint and posterior subtalar joint .
The tarsal sinus contains blood vessels, nerves, fat and a ligamentous complex, which is comprised of :
- medial, intermediate and lateral roots of the inferior extensor retinaculum
- lateral cervical ligament
- medial talocalcaneal interosseous ligament (ligament of the sinus tarsi)
By some authors , the ligaments are seen as one single structure and referred to as the fundiform ligament with one lateral and one medial band.
Fibers of the lateral inferior extensor retinaculum also traverse the tarsal sinus and canal, where they are anchored to the talus and calcaneus. The interosseous talocalcaneal ligament and the medial component of the extensor retinaculum root form a V-shape in the tarsal sinus and canal.
The talocalcaneal interosseous ligament controls the talus in the movements of eversion and inversion by maintaining apposition of the talus and calcaneus. The function of the cervical ligament is to limit inversion of the hindfoot. The inferior extensor retinaculum assists the cervical ligament in limiting inversion of the subtalar joint. With dorsal extension of the toes, the ligamentous complex forms a control mechanism for the longitudinal arch of the foot in the moving phase.