Figure 1 Patella height measured onlateral radiograph of the weight-bearing flexed knee. A shows ISI=a/b；B shows Caton de Champs index=c/d；C shows BPI=e/f

Figure 2 The method for measuring the patellar position on the axial radiograph of the knee joint. A is lateral patellofemoral joint angle; B is lateral displacement of the patella (the distance between the vertical lines of lateral pole of the patella and the lateral apex of the femoral pulley to the line connecting posterior condyles of the femur.); C is lateral patellar inclination angle (using the line connecting the projection points of the posterior condyles on the axial radiograph as reference line); D is patellar inclination angle (using the line connecting the projection points of posterior condyles on the axial radiograph as reference line)

Figure 3 Heat map of the relative position of the average model of the patellar surface and the trochlear plane Note: This heat map was calculated and analyzed under the bi-plane orthogonal fluoroscopy imaging system at the same stance during the stair-climbing motion cycle of 14 patients before surgery and six months after surgery. (the direction in which the patellar surface is closer to the trochlear surface is positive, unit: mm)