The superior peroneal retinaculum is one of two fibrous bands that bind the peroneus longus and peroneus brevis muscle tendons that run over the ankle's lateral side. While these muscles stabilize the lateral ankle and evert (bend outward) the foot, the superior peroneal retinaculum creates a fibro-osseous (composed of both fibers and bone) tunnel from the retromalleolar groove, working to prevent peroneal subluxation, a condition in which the peroneal tendons snap out of place.
The superior peroneal retinaculum is also known as the external annular ligament. Its fibers are connected to the lateral malleolus (the bony projections at the outside of each ankle) and the calcaneus's (heel bone) lateral surface.
Superior peroneal retinaculum injuries, as well as diseases such as tenosynovitis, can cause pain and instability in the lateral ankle. Fortunately, such conditions can be corrected by reconstructive surgery, which directly repairs the ankle's superior peroneal retinaculum; however, this is difficult in patients with insufficient structural remnants.