Variations in the insertion of the extensor hallucis longus muscle.

Reports that describe abnormalities of the muscles and tendons of the leg and foot are important with regard to understanding the function of the lower limb and correlating these abnormalities with the clinical aspects. Variations in the insertion of the extensor hallucis longus muscle were studied in 60 adult human cadavers. Three different patterns of insertion were noticed. Pattern I (65%): the extensor hallucis longus muscle had a single tendinous insertion on the dorsal aspect of the base of the distal phalanx of the big toe. Pattern II (26.67%): the muscle terminated in two tendons. Pattern III (8.33%): the muscle terminated in three tendinous slips. Various sites of insertion of the extensor hallucis longus muscle were recorded other than the dorsal aspect of the base of the distal phalanx of the big toe. These were the dorsal aspect of the base of the proximal phalanx of the big toe and the capsule of the first metatarso-phalangeal joint or a connection with the tendon of the extensor hallucis brevis. The frequency of occurrence of lateral deviation of the big toe at the metatarso-phalangeal joint (hallux valgus) was recorded. It is suggested that the presence of these variations in the insertion of the extensor hallucis longus muscle may have a role in explaining its association with hallux valgus.