Fig. 2

Legnth measurement and Second calibration. a Measurement of femur length, tibia length, leg length after first calibration. The leg length was measured from the highest point of the femoral head to the center of the distal tibia. The femur length was measured from the highest point of the femoral head to the middle of the femoral intercondylar fossa. The tibia length was measured from the middle of tibial plateau to the middle of articular surface of the distal tibia. b Second calibration: An example of underestimation of leg length due to splicing error. Line AB denotes the preoperative femur length. Line AC denotes the preoperative tibia length. Line BC denotes the preoperative leg length. Line DE denotes the post-operation femur length. Theoretically, line DE should be equal in length to line AB, but in actuality, line DE was shorter than line AB. We extended line DE to point F so that line DF is the same as line AB. Line EF denotes the longitudinal splicing error of the femoral end, and line JF was the "contribution value" of the change of leg length. The diagram applies to the tibial side as well. The real postoperative leg length (line FH) is line EG plus the lost length (lines FJ and IH) due to longitudinal splicing error