Primary End-to-End Repair of Subacute Extensor Hallucis Longus Tendon Rupture Supported by a Preserved Extensor Hallucis Capsularis: A Case Report.

Extensor hallucis longus (EHL) tendon rupture is an uncommon injury that usually results from trauma and often requires surgical intervention. In the subacute phase, primary tendon repair becomes challenging because of tendon retraction, and tendon transfer or graft reconstruction is often necessary. Anatomical variations of the EHL, particularly the extensor hallucis capsularis (EHC), may influence tendon retraction and reparability, although their clinical significance has rarely been reported. We present a rare case of subacute EHL rupture in which primary end-to-end repair was feasible owing to the presence of a preserved EHC. The purpose of this case report is to highlight the surgical and anatomical significance of the EHC, specifically the Olewnik Type IIb variant, in preserving tendon alignment and enabling delayed primary repair. A 26-year-old woman presented with loss of hallux extension 1 week after a sharp laceration. Magnetic resonance imaging revealed complete EHL rupture. During surgery performed 11 days postinjury, the EHC was identified as a medial accessory tendon inserting distal to the extensor hallucis brevis insertion, consistent with the Olewnik Type IIb classification. The EHC appeared to prevent proximal tendon migration, leaving a 5-mm tendon gap and enabling a six-strand Yoshizu Type I repair. Rehabilitation began at 2 weeks, and by 12 weeks the patient achieved full strength and motion without complications. This case demonstrates that preservation of the EHC can maintain partial extensor mechanism continuity and may expand the indications for primary repair in carefully selected subacute cases. Awareness of this anatomical variant may assist in preoperative planning and surgical decision-making.