What we know about the inferior extensor retinaculum (IER} of the foot:
- Aponeurotic Y- or X-shaped structure located at the anterolateral aspect of the ankle and tarsal bones that is continuous with the sural fascia.
- Runs from the tip of the lateral malleolus to the lateral calcaneus and sinus tarsi (ST}; blends with the inferior fibular retinaculum and may improve evertor muscle function.
- The root of the IER, aka frondiform ligament, has lateral, intermediate, and medial parts. It forms a sling around the extensor digitorum longus and peroneus tertius tendons, securing them against the talus and calcaneus (and preventing the bowstringing effect) (Figures 1 and 2).
