Fig. 1

Measurement of prosthesis angles, TFA and PCO. a shows the sagittal plane of the knee joint, AB is the anatomical axis of the distal femur, and CD is the longitudinal axis of the femoral prosthesis. The angle between the two is the FPFA. The angle between EF and GH is the tibial prosthesis slope. b shows the coronal plane of the knee. The angle between IJ and KL is the femoral prosthesis valgus angle. The angle between MN and OP is the tibial prosthesis valgus angle. The angle between IJ and OP is the TFA. c the red solid line is the surgical transepicondylar axis, and the dotted line is the posterior condylar line of the femoral prosthesis. The angle between the two is the femoral prosthesis rotation angle. The angle between the vertical line (ST) of the surgical transepicondylar axis and QR is the tibial prosthesis rotation angle. d the distance between the tangent line of the posterior femoral cortex (red solid line) and the tangent line of the posterior condyle apex (red dashed line) is the PCO