Gender differences in the distal femur dimensions and variation patterns in relation to TKA component sizing

Matching femoral components with distal femurs in female patients can be difficult. The purpose of this study was to determine the validity of the following hypotheses: (1) Anteroposterior (AP) dimensions do not increase proportionately to medial-lateral (ML) dimensions in men and women. (2) The AP/ML ratio is different in men and women. (3) The AP/ML ratios of femoral implants and the variations in ratios are more in line with data from men than women. Magnetic resonance imaging of the knees of 50 consecutive male patients and 50 consecutive female patients were studied. Both groups had similar age distribution. Anteroposterior and ML dimensions were measured, and AP/ML ratios were obtained and plotted. Inside AP and ML dimensions of 8 popular total knee arthroplasty (TKA) systems produced by 6 manufacturers were obtained. The AP/ML ratio for women was 0.80 (SD=.05), whereas that for men was 0.76 (SD=.03). This study demonstrated a significant difference in distal femur proportions between men and women. Dimensions propagation of femoral components for TKA followed significantly closer to men's distal femur dimensions variation than to that of women.