A retinaculum refers to any region on the body where tendon groups from different muscles pass under one connective tissue band. The inferior extensor retinaculum is located at the front of the ankle joint and is Y-shaped. The stem of this Y-shaped band is attached in a lateral (sideways) direction to the calcaneus bone’s upper surface. (The calcaneus is the medical term for the heel bone.) This band is also located in front of the interosseous talocalcaneal ligament, which is what forms the union bond between the calcaneus and the talus, or ankle bone.
The inferior extensor retinaculum is considered a double layer due to one lamina (thin sheet) passing behind and the other passing in front of the tendons of the extensor digitorum longus and the peroneus tertius. The extensor digitorum longus muscle is located on the lateral (side) portion of the front part of the leg. The peroneus tertius muscle is also located in the lower limb. The two layers of the inferior extensor retinaculum come together to form a compartment that encloses these tendons.
Near the band’s middle, the Y’s two limbs split — one going upward, toward the ankle, and the other toward the middle of the foot — and both pass over the tendon of the extensor hallucis longus. The upper portion attaches to the tibial malleolus (the inner-bottom of the shinbone) and the other attaches to the plantar aponeurosis, a thick band of tissue in the arch of the foot.