The patients' knees were taken on the X-ray examination after the total knee arthroplasty on the medial-lateral position. The flexion (positive degree) or extension (negative degree) angle of the femoral component according to the anterior femoral cortex was measured. The patients with the sagittal flexion angle of the femoral component less than 4° were categorized into this group.

The patients' knees were taken on the X-ray examination after the total knee arthroplasty on the medial-lateral position. The flexion (positive degree) or extension (negative degree) angle of the femoral component according to the anterior femoral cortex was measured. The patients with the sagittal flexion angle of the femoral component over 4° were categorized into this group.

The surgeries were performed under general anesthesia. The medial parepatellar incision was introduced during the TKA. The femoral component size was selected according to the intro-operative measurement. The osteotomy was done according to the intramedullary guide and the cutting guide. After the proximal tibial osteotomy was finished, the cruciate-retaining Total Knee System was used. The lateral rotation of the femoral component was determined by the gap-balancing technique.

The posterior femoral offset was defined as the maximal thickness of the posterior condyle projecting posteriorly to a straight line drawn as the extension of the posterior femoral shaft cortex on the medial-lateral position of the X-ray examination.

The posterior femoral offset ratio was defined as the maximal thickness of the posterior condyle projecting posteriorly to a straight line drawn as the extension of the posterior femoral shaft cortex, divided by the maximal thickness of the posterior condyle projecting posterior to a straight line drawn as the extension of the anterior femoral shaft contex on the medial-lateral position of the X-ray examination.