Fig. 2

Direct magnetic resonance arthrography of a 30-year-old woman with right developmental dysplasia of the hip. The image shows the measurement and calculation of the femoral neck anteversion (FNA) angle. The cross section of the knee joint and the cross section of the femoral neck are sequentially measured. The axial femoral plane angle is added or subtracted with the intersection angle of the hypocondyle angle and the horizontal line of the knee joint. Angle’s addition is for knee internal flip and angle’s subtraction is for the knee external flip. a cross section image of the hip; b cross section image of the knee