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Example of alpha angle measurement. A best-fit circle was first drawn around the femoral head and the centre was defined. A line was then drawn parallel to the femoral neck axis from the head centre. A second line was drawn from the head centre to the point at which the femoral head/neck fell outside of the best-fit circle. The alpha angle was measured between these two lines. (A) Shows an alpha angle>55° (70.6°) and (B) shows an alpha angle<55° (52.2°).
