Superior fibular retinaculum

The superior fibular retinaculum (Superior peroneal retinaculum) is a distinct, fibrous band located on the lateral aspect of the ankle. It extends from the posterolateral margin of the lateral malleolus (fibula) to the lateral surface of the calcaneus, forming the roof of the superior peroneal tunnel through which the peroneal tendons (peroneus longus and brevis) pass. The retinaculum is composed of densely packed, parallel collagen fibers, with minimal loose connective tissue and no elastic fibers, and is intimately associated with the deep fascia of the leg.

The retinaculum attaches proximally to the periosteum of the fibula at the lateral aspect of the retromalleolar groove, and distally to the calcaneus. The floor of the tunnel beneath the retinaculum consists of both an osseous component (the retromalleolar groove of the fibula, which is consistently concave) and a non-osseous component (the lower part of the posterior intermuscular septum of the leg).

The retinaculum is typically about 1 mm thick and appears as a low-signal-intensity band on MRI and ultrasound.

Functionally, the superior fibular retinaculum stabilizes the peroneal tendons, preventing their subluxation or dislocation during ankle movement. It may also form an aponeurotic connection with the lateral septum of the calcaneal tendon and the superior part of the posterior fibulotalocalcaneal ligament complex.