Fig. 2From: Magnetic Resonance Arthrography, a valuable pre-operative imaging modality in femoro-acetabular impingementMeasurement of the alpha angle is shown. A best-fit circle is drawn over the femoral head. The alpha angle is formed by the axis of the femoral neck (1) and a line (2) drawn from the femoral head center to the point where the head extends beyond the margin of the best fit circle (arrow)Back to article page