Endoscopic excision for posterior ankle impingement secondary to chronic fragmented os trigonum fracture: a case report.

Chronic fragmented os trigonum fracture is an uncommon but clinically important cause of posterior ankle impingement that may be overlooked in active patients with persistent plantar-flexion-related posterior ankle pain. We report the case of a 31-year-old female physical education teacher with progressive right posterior ankle pain for over 1 year despite 3 months of conservative treatment. Radiographs and magnetic resonance imaging demonstrated a fragmented os trigonum with bone marrow edema and reactive inflammation. Posterior ankle endoscopy confirmed three osseous fragments, which were excised sequentially. Pain resolved within 3 weeks, light running resumed at 8 weeks, and full return to preinjury sports was achieved at 3 months. At 5-year follow-up, the patient remained asymptomatic with no recurrence and complete functional recovery. This case highlights the importance of considering this diagnosis in active patients with persistent posterior ankle pain and supports posterior ankle endoscopy as an effective treatment with durable results.