From the question on page 536

Diagnosis

Femoroacetabular Impingement (FAI).

Findings

The plain radiograph shows a synovial herniation pit within the femoral neck (arrow, fig 1). The MR arthrogram found a tear of the anterior–superior labrum (arrow, fig 3). MRI also showed an osseous prominence or “bump” on the anterior femur at the femoral head–neck junction (fig 2, arrow), with associated subchondral cystic change, consistent with cam-type femoroacetabular impingement (FAI).

The alpha angle gives an estimate of the lack of sphericity to the femoral head–neck junction and is the angle between the axis of the femoral neck and the point where the femoral head–neck junction leaves the spherical contour of the femoral head. A good diagram of the alpha angle calculation is available elsewhere.1 Larger alpha angles are seen as the femoral head becomes less spherical at the level of the femoral head–neck junction. The patient had an abnormally increased alpha angle of 63 degrees.

The patient failed a nonoperative treatment course consisting of activity modification, nonsteroidal anti-inflammatory medication and physiotherapy. She was subsequently referred for surgery and underwent right hip arthroscopy, labral repair …