Obturator internus avulsion in adolescents: a rare pattern of pelvic avulsion injury.

Obturator internus (OI) avulsion at its pelvic origin is an exceptionally rare cause of acute hip and groin pain in adolescents and is often radiographically occult. We report two adolescent boys with acute, severe hip pain and inability to ambulate after distinct mechanisms; one during a basketball jump without direct trauma and the other following a direct fall onto the hip. In both cases, pelvic and hip radiographs were normal. Magnetic resonance imaging established the diagnosis and revealed a strikingly similar constellation of findings in both patients: medial displacement and bowing of the OI away from the pelvic side wall with extensive muscle edema along its course extending through the sciatic notch, interposed fluid at the pelvic attachment, associated ipsilateral gluteus minimus edema, and a small-to-moderate hip effusion. Critically, a focal area of T1 hyperintensity deep to the displaced OI consistent with hemorrhage supported traumatic avulsion and helped distinguish this entity from infectious or inflammatory processes. Both patients were treated nonoperatively with protected weightbearing, activity modification, and physical therapy, with return to high activity at 1 year and 2.5 years. This report highlights a rare injury with a distinct and reproducible MR pattern that should alert radiologists and treating clinicians, enabling timely diagnosis and avoiding unnecessary investigations.