BACKGROUND: Os subfibulare (OS) is commonly found in patients with chronic lateral ankle instability (CLAI). When performing lateral ligament reconstruction for CLAI, excision of a large OS can cause substantial lateral ligament defects making anatomic repair challenging. This study analyzed clinical and radiologic outcomes among patients who underwent osteosynthesis of the OS for chronic lateral ankle instability and a large OS. METHODS: 28 ankles with CLAI and a large OS (≥10 mm) that underwent osteosynthesis of the OS between June 2007 and July 2021 were included in the study and followed for ≥24 months. Visual analog scale (VAS) for pain, Karlsson-Peterson ankle score, and Medical Outcomes Study Short Form Health Survey-36 physical component summary (SF-36 PCS), talar tilt angle, and anterior displacement of the talus were used to assess clinical and radiologic outcomes. All reoperations and complications were also evaluated. RESULTS: The mean OS size was 15.4 mm (range, 12.2-21.0 mm). The mean follow-up period was 78.9 months (range, 24.0-177.0 months). Mean VAS score, Karlsson-Peterson ankle score, SF-36 PCS, talar tilt angle, and anterior displacement of the talus all improved significantly, from preoperative values of 5.3 ± 1.8, 38.4 ± 10.6, 45.6 ± 10.8 points, 11.1 ± 5.7 degrees, and 7.3 ± 1.9 mm, to 0.9 ± 1.4, 88.7 ± 12.6, 80.2 ± 12.3 points, 3.9 ± 2.0 degrees, and 4.8 ± 1.3 mm, respectively, by the last follow-up. The overall complication rate was 10.7% (3 ankles)
the reoperation rate was 7.1% (2 ankles). CONCLUSION: Osteosynthesis of the OS produced satisfactory outcomes in patients with CLAI and a large OS. This method may be a viable surgical option for patients with this condition.