Point A is the center of the femoral head and the line drawn from A to B is the long axis line connecting the centers between the femur head and neck. The line drawn from A to C is the line extending from the center of the femoral head to the point the femoral head extrudes a circle drawn around the femoral head. The angle formed between these two lines is defined as alpha. The alpha angle is described as the angle formed by the femoral neck axial line and the line from the center of the femoral head to a point where the femoral head extends outside the circle around the femoral head.