Flexor retinaculum of foot

The flexor retinaculum of foot (laciniate ligament, internal annular ligament) is a strong fibrous band, extending from the bony ankle prominence (malleolus) above, to the margin of the heelbone (calcaneus) below, converting a series of bony grooves in this situation into canals for the passage of the tendons of the flexor muscles and the posterior tibial vessels and tibial nerve into the sole of the foot.

It is continuous by its upper border with the deep fascia of the leg, and by its lower border with the plantar aponeurosis and the fibers of origin of the abductor hallucis muscle.

Enumerated from the medial side, the four canals which it forms transmit the tendons of the tibialis posterior and flexor digitorum longus muscles; the posterior tibial vessels and tibial nerve, which run through a broad space beneath the ligament; and lastly, in a canal formed partly by the talus, the tendon of the flexor hallucis longus.

The entrapment of the tibial nerve beneath the laciniate ligament causes tarsal tunnel syndrome, characterized by pain, numbness and tingling of the medial plantar surface of the foot. The situation is aggravated by standing and walking, and often worse at night.