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The absence of peroneus tertius muscle on the dorsum of the foot.

Authors:Sharadkumar Pralhad Sawant, Shaguphta T. Shaikh, Rakhi Milind More
Int J Biol Med Res. 2012; 3(4): 2633-2635  |  PDF File


Peroneus tertius (fibularis tertius) is a uniquely human muscle. It often appears to be part of extensor digitorum longus, and might be described as its ‘fifth tendon’. The muscle fibres operating on this tendon arise from the distal third or more of the medial surface of the fibula, the adjoining anterior surface of the interosseous membrane, and the anterior crural intermuscular septum. The tendon passes behind the superior extensor retinaculum and within the loop of the inferior extensor retinaculum it shares with extensor digitorum longus. Peroneus tertius lies lateral to extensor digitorum longus. It is inserted into the medial part of the dorsal surface of the base of the fifth metatarsal bone, and a thin expansion usually extends forwards along the medial border of the shaft of the bone.During routine dissection for the first MBBS students, we observed that the peroneus tertius was absent on the dorsum of the left lower limb of a 70 years old, donated embalmed male cadaver in the Department of Anatomy, K.J.Somaiya Medical College,Sion,Mumbai,India. The photographs of the dorsum of the foot were taken for proper documentation and for ready reference. The absence of the peroneus tertius is very rare and not found in literature. Usually, the peroneus tertius is involved in dorsiflexion and eversion of the foot. The existence of peroneus tertius may help in the swing phase of bipedal walking. The peroneus tertius may be used for tendon graft surgeries. The pull of the peroneus tertius may be responsible for causing stress on the fifth metatarsal bone and account for all stress fractures in any individual. The absent peroneus tertius may misguide foot surgeons performing graft operations and transplant. The absent peroneus tertius is an interesting finding, which could be clinically important for Anatomists, Anthropologists, Surgeons and Orthopedic surgeons.