Bilateral absence of fibularis tertius: clinical implications and phylogeny

Fibularis tertius (FT) muscle is found in the anterior compartment of the leg. It assists in dorsiflexion and eversion of foot. The FT muscle originates from the distal third of the medial surface of fibula, the adjoining interosseous membrane and the anterior intermuscular septum. It is inserted on the dorsal surface of the base of the fifth metatarsal. During routine dissection of an adult female cadaver, a bilateral absence of FT was observed. Cases of absence of FT may be asymptomatic; it may be accidentally detected during dissection or autopsies. FT when present, may act in swing phase of gait. Its tendon may be used in transplantation and treatment of ankle laxity. Stress fracture of the fifth metatarsal may be produced by the pull of FT. Surgeons planning tendon transplants might be perplexed by absence of FT. The clinical implications and phylogeny of the bilateral absence of FT are discussed.