Flexor Digitorum Longus, Plantar View

Description

Plantar anatomy of the male right foot is centered on the flexor digitorum longus as it courses from the deep posterior compartment of the leg into the sole. Proximally, the muscle belly arises from the posterior surface of the tibia, then its tendon passes posterior to the medial malleolus within the tarsal tunnel, deep to the flexor retinaculum and alongside the tibialis posterior and flexor hallucis longus tendons. Distal to the calcaneus, the tendon enters the plantar midfoot, crosses the flexor hallucis longus at the chiasma plantare (knot of Henry), then divides into four slips that run anteriorly to digits two through five and insert on the bases of the distal phalanges. The medial longitudinal arch sits superficial to this track. Teaching the plantar course of flexor digitorum longus matters because its tendon is a frequent landmark in medial ankle and hindfoot surgery and a common source of referred plantar pain when tenosynovitis develops in the tarsal tunnel. Compression of the tibial nerve beneath the flexor retinaculum (tarsal tunnel syndrome) is often discussed in relation to these tendons and their synovial sheaths, and surgeons routinely harvest or transfer the flexor digitorum longus to augment the posterior tibial tendon in adult acquired flatfoot deformity. Small details, like the crossing with flexor hallucis longus, explain why pathology can couple hallux and lesser toe flexion. A tight space. Use this illustration in lower limb anatomy courses when contrasting dorsal extensors with plantar flexors, in podiatry and orthopaedic teaching files covering the tarsal tunnel and medial ankle approach, or in surgical texts describing flexor digitorum longus tendon transfer and knot of Henry dissection in the plantar midfoot. Anatomical accuracy verified by SciePro's Medical Advisory Board.