Figure 2: Schematic drawing of the measurement of the NSA (a) and mNSA (b). The NSA requires the definition of the centre of rotation and the waist of the femoral neck to define the femoral neck axis (FNA). Two circles in the femur are drawn to define the long femoral axis (FLA). The NSA is the angle between the FLA and FNA (a). The mNSA requires no FNA. A perpendicular to the FLA is drawn, cutting the apex of the minor trochanter. The cutting point of both axes is connected to the centre of rotation; the angle between this axis and the FLA is the mNSA.