As for the number of patients who requires total knee arthroplasty (TKA), Asian-Pacific countries will be the most important market. However, due to the paucity of anthropometric data on the proximal tibia in this population, many prostheses designed for Caucasian knees have been introduced without specific modification.The aim of the current study was to analyze the geometry of the proximal tibia to design the optimum component for the Japanese population.

Anthropometric data on the proximal tibia of 100 knees in 80 patients undergoing TKA was obtained. Briefly, anterior-posterior (AP) and medial-lateral (ML) lengths were measured with a combination of two different methods, namely on the computed tomography (CT) images obtained preoperatively and intraoperative direct measurement on tibial resection surface. Reproducible measurement was possible only when the intraoperative measurement was combined with the corresponding CT images while the direction of measurements being aligned to the epicondylar axis of the femur.

It was shown that smaller components with an ML of around 60 mm were rarely required. Tibial component size variation should focus on an ML length of 65 to 75 mm because 76 of 100 knees (76 %) fell into this size range. When the subjects were confined to women, 70 of 77 knees (91%) were included in this size range. The intraoperative AP to ML ratio had a negative correlation with the ML length (r = −0.412, P < 0.0001) indicating that bigger knees were shallower in the AP direction. The size variation of currently popular pros-theses were not in accordance with the geometry of the tibial resection surface shown in this study.

The results of this study applied to a cross-section of the Japanese population can be used by manufacturers to create a prosthesis suitable for most of the Asian-Pacific population.

The purpose of this study was to investigate the bone anatomy in determining the rotational alignment in total knee arthroplasty (TKA) using CT scan. Axial CT images of eighty-four varus osteoarthritic knees undergoing TKA were analysed. On the images of the distal femur and the proximal tibia, base line for anterior-posterior axis of each component was drawn based on the epicondylar axis for the femur and medial one-third of the tibial tuberosity for the tibia. Angle between these two lines was analysed as the rotational mismatch between the components when they were determined based on the anatomical landmark of each bone. Thirty-eight knees (45%) showed more than 5-degree mismatch and seven knees (8.3%) showed the mismatch more than 10-degree. There was a tendency to put the tibial component in external rotation relative to the femoral component when they were aligned to medial one-third of the tibial tuberosity. The results have indicated that the landmark of each bone was the intrinsic cause of the rotational mismatch between the components. The surgeons performing TKA surgery should aware of this fact and should align the tibial component in a compromised position, if necessary, to have overall satisfactory clinical outcome.