Fig 2.

(A and B) Radiographic imaging of a left hip demonstrating the alpha angle measurement. In order to accurately measure the alpha angle, a line should be drawn from the center of the narrowest point of the femoral neck to the center of the femoral head using a best-fit circle. The alpha angle is between the line down the axis of the femoral neck and a line drawn to the location where the femoral head loses its sphericity. Alpha angles >55° are indicative of cam femoroacetabular impingement deformity, and normal alpha angles are typically considered to be <55°.