Independent muscle of extensor hallucis capsularis: a cadaveric case report

Extensor hallucis capsularis (EHC) is an accessory tendon located medially to extensor halluces longus (EHL) tendon. Most EHC is known to originate as a tendinous slip of the EHL tendon, although it may be splitted from the tibialis anterior (TA) tendon or the extensor halluces brevis (EHB) tendon. During routine dissection of a 49-year-old male cadaver, independent muscle bellies of EHC were discovered bilaterally. The EHL muscle arose from the middle anteromedial aspect of fibula, lateral to the origin of TA muscle and medial to extensor digitorum longus (EDL) muscle. An additional muscle bellies were separated from EHL muscle at the point of 6 cm away from EHL origin in the right leg, and 3 cm away in the left. They coursed downward as EHC to reach the first metatarsophalangeal joint capsule. This muscle, unlike the variations identified to date, is considered to extend to EHC, and the name "extensor hallucis capsularis muscle" is offered. This kind of variation may be important for investigating the development of deformity at the first metatarsophalangeal joint, such as hallux valgus.