Inferior fibular retinaculum

The inferior fibular retinaculum (Inferior peroneal retinaculum) is a distinct band of thickened deep fascia located on the lateral aspect of the ankle and foot, inferior to the lateral malleolus, extending from the lateral calcaneus (specifically, the peroneal tubercle) and blending proximally with the inferior extensor retinaculum and distally with the deep fascia of the foot. It is firmly attached to the lateral surface of the calcaneus and the fibular trochlea (peroneal tubercle), which serves as a key landmark for its distal attachment.

This retinaculum forms a fibrous tunnel that stabilizes the tendons of the fibularis (peroneus) longus and brevis muscles as they pass posterior to the lateral malleolus and then inferiorly along the lateral calcaneus. The structure is typically 0.8–1.0 mm thick and appears as a low-signal-intensity band on MRI, with a crisscross, lattice-like arrangement of collagen fibers, providing mechanical strength and preventing tendon subluxation or bowstringing during ankle movement.The inferior fibular retinaculum is continuous with the deep fascia and its function remains the stabilization of the peroneal tendons.