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

Area of Science:

• Anatomy
• Orthopedics
• Biomechanics

Background:

• Inconsistent data exists regarding the hallucal extensor apparatus, accessory tendon slips, and their functions.
• Clarifying the anatomical features and functional roles of these structures is necessary.

Purpose of the Study:

• To investigate the anatomical characteristics of the hallucal extensor apparatus.
• To determine the function of accessory extensor tendons, specifically the extensor hallucis capsularis (EHC).

Main Methods:

• Prospective investigation during operative correction of hallux valgus and interphalangeus in 60 patients.
• Recording occurrence, location, size, and insertion patterns of accessory extensor tendons.
• Intraoperative dissection and traction to assess tendon function.

Main Results:

• Consistent anatomical findings revealed an accessory medial extensor hallucis longus tendon (EHC) in 98.3% of cases.
• The EHC consistently inserted on the dorsomedial aspect of the metatarsophalangeal joint capsule.
• Intraoperative testing demonstrated the EHC's role in pretensioning the metatarsophalangeal joint capsule.

Conclusions:

• The extensor hallucis capsularis (EHC) is a consistent anatomical feature, present in 98.3% of individuals studied.
• The EHC's primary function is to pretension the metatarsophalangeal joint capsule, preventing impingement during hallucal extension.
• The high incidence of EHC suggests a potential correlation with MTP joint deformities, warranting further cadaveric studies for hallux valgus predisposition.