The extensor hallucis capsularis tendon--a prospective study of its occurrence and function.

Abstract

There is inhomogeneous data about the hallucal extensor apparatus and the occurrence of accessory tendon slips and their function. We performed this study to clarify its anatomical features and make conclusions about its function. Investigations were performed prospectively during operative correction of severe hallux valgus and interphalangeus in 60 consecutive cases. The occurrence, topographic location and size of accessory extensor tendons as well as the insertion patterns were recorded. After dissection traction of the accessory tendon was carried out to gain information about its function. In contradiction to previous studies reporting numerous variations in the distal attachments of the hallucal extensor apparatus with different accessory tendons described, our investigations showed constant anatomical features. In all but one case (98.3%) there was an accessory medial extensor hallucis longus tendon adjacent to the main tendon, always inserting on the dorsomedial aspect of the metatarsophalangeal joint capsule. We therefore chose the terminology extensor hallucis capsularis (EHC) used in previous studies. The intraoperative testing of the tendon showed it to exert a pretension of the metatarsophalangeal (MTP) joint capsule. Our study showed consistent anatomical features with an occurrence of the EHC tendon in 98.3%. We determined that its function is to pretension the MTP joint capsule, therefore avoiding capsular impingement during hallucal extension. The high incidence of the EHC tendon in our study may also postulate a correlation with MTP joint deformities and further cadaveric studies will be necessary to evaluate a possible predisposition for hallux valgus genesis.