The accessory extensor tendon of the first metatarsophalangeal joint.

The accessory extensor tendon of the first metatarsophalangeal joint (1st MTPJ) was evaluated in 32 cadaver feet. Eighty-one percent of feet possessed an accessory tendon to the 1st MTPJ. Of those feet possessing an accessory tendon to the 1st MTPJ, approximately 92% originated from the extensor hallucis longus muscle-tendon unit, while approximately 8% originated from the tibialis anterior muscle-tendon unit. All accessory tendons inserted onto the dorsal/dorsomedial capsule of the 1st MTPJ. Accessory tendons were found to be bilateral in the majority (87.5%) of specimens. Differences in sex distribution of the accessory tendon of the 1st MTPJ were not statistically significant. The difference in distribution of an accessory tendon to the 1st MTPJ in those feet that demonstrated clinical hallux valgus versus those that did not demonstrate hallux valgus was not statistically significant (p = 1.0000, respectively, Fisher's exact test). This tendon is unique to the human foot (lacking in primates) and is a fairly constant structure (80%). The data presented do not lend support for the accessory tendon of the 1st MTPJ to play a role in the development of hallux valgus. At the present time, the role of this accessory tendon on the biomechanics of the 1st MTPJ remains unknown.