Significance of variations in the interconnection between flexor digitorum longus and flexor hallucis longus of the lower limb

Introduction Flexor digitorum longus, flexor hallucis longus and tibialis posterior are the three deep muscles of the posterior compartment of the leg. Flexor digitorum longus arises from the posterior surface of tibia below the soleal line medial to tibialis posterior, and by a broad tendon from the fibula, then courses deep to the flexor retinaculum in the tarsal tunnel to enter the sole of foot. In the sole, the flexor digitorum longus muscle passes superficial to flexor hallucis longus tendon, crosses it from medial to lateral side, and divides into four tendons which insert into the plantar surface of the base of distal phalanx of the lateral four toes [1]. The tendon of flexor digitorum longus receives a strong slip from the tendon of flexor hallucis longus (and may also send a slip to it, so called knot of Henry) [2]. Flexor hallucis longus is a powerful plantar flexor of the foot, and arises from the inferior two thirds of the posterior surface of fibula and inferior part of interosseous membrane, and inserts into the base of distal phalanx of great toe. Flexor hallucis longus, as it crosses the flexor digitorum longus in the sole of foot at the knot of henry, gives strong slips to its medial two tendons (for the second and third toes). The connecting slip to flexor digitorum longus varies in size: it usually continues into the tendons for the second and third toes but sometimes restricted to the second (present case) and occasionally extends to the fourth [2]. Multiple accessory, supernumerary and variant muscles have been described in the anatomical, radiological and surgical literature. Present case reports a connecting slip from flexor digitorum longus tendon to flexor hallucis longus tendon on the left side and from flexor hallucis longus tendon to flexor digitorum longus tendon on the right side.