Anterior inferior iliac spine avulsion

This is a case of a 14 year old girl who runs for her high school cross country team presenting with a 1 month history of hip pain. A radiograph of the pelvis demonstrates periarticular mineralization adjacent to the right hip. Specifically, the calcification is at the level of the anterior inferior iliac spine. Findings are most consistent with a subacute avulsion fracture of the anterior inferior iliac spine (AIIS). The AIIS is the site of origin for the rectus femoris muscle, one of the muscles in the quadriceps muscle group. Forceful flexion, especially in skeletally immature patients such as adolescents, can result in avulsion as well as either a partial or full thickness tendon tear. Patients often describe a sudden pop or snap at the time of initial injury followed by the onset of pain.