Figure 1.

Frog-leg lateral radiograph of a patient with a cam lesion. The alpha angle is measured by drawing a perfect circle around the femoral head and identifying the point where the contour of the femoral head leaves this circle. A line is drawn down the center of the femoral neck and through the center of the perfect circle. A second line is drawn through the center of the circle and through the point where the femoral head leaves the perfect circle. The angle between these 2 lines represents the alpha angle. An angle greater than 55° was considered radiographic evidence of a cam lesion.