Flexor Hallucis Longus

Description

Running along the posterior aspect of the fibula, the flexor hallucis longus muscle belly occupies the deep posterior compartment of the left leg and tapers distally into a stout tendon. That tendon courses inferiorly, passing posterior to the talus and then deep to the flexor retinaculum within the tarsal tunnel, where it lies lateral to the flexor digitorum longus tendon and posterior tibial vessels but medial to the calcaneal tuberosity. Adjacent bony landmarks would logically include the tibia medially, the fibula laterally, and the medial malleolus forming the roofline of the tunnel. Proximally, the relationship to the distal femur at the knee is only partial and serves as orientation. Deep posterior compartment anatomy is easiest to misunderstand at the ankle, and this route explains common exam findings. Flexor hallucis longus tenosynovitis can cause posteromedial ankle pain and pain with resisted hallux flexion, and the tendon is vulnerable where it changes direction behind the talus and under the sustentaculum tali. Tarsal tunnel syndrome is classically neurogenic, but local tendon sheath thickening and space-occupying synovitis can contribute to crowding beneath the flexor retinaculum, a point that matters when correlating symptoms with operative release. Use this artwork when you need to teach the layered contents of the tarsal tunnel, tendon gliding mechanics, or the distal course of the flexor hallucis longus from leg to foot in gross anatomy, podiatry, sports medicine, or orthopaedic texts. It also supports surgical and ultrasound teaching on posteromedial ankle approaches and tendon pathology mapping. Anatomical accuracy verified by SciePro's Medical Advisory Board.