Total knee replacement has proven to be a very successful procedure. However, problems have been encountered in fitting standard femoral implants to distal femurs using various popular total knee replacement systems.

Authors observed that difficulties matching femoral components with distal femurs most frequently occurred in female patients. In practice, as far as femoral sizing is concerned, women are just treated as small men.

Despite an extensive English literature search, only a limited number of studies addressing the gender differences in distal femurs proportions were identified.

In view of our experiences, we hypothesize that 1) Anterior-posterior (AP) dimensions do not increase in the same proportion to medial-lateral (ML) dimensions in men and women. 2) The AP/ML ratio is different in males and females. 3) Femoral implants AP/ ML ratios are more inline with men ratios then with women

Materials and Methods: In order to test the hypothesis, 50 male and 50 female patients consecutive knee MRI scans of the knee were studied. The patients were referred to UMC MRI Center with a variety of diagnoses. The knees involved with conditions distorting bony anatomy were excluded. The age distribution of the patients ranged from 17 to 77 years for the males and 17 to 85 years for the females.

Evaluation was focused on axial views of the distal femur. A cut with the maximum medial lateral dimensions of a studied femur was selected. The ML measurement was made along the epicondylar axis. The maximum AP dimension was obtained perpendicular to the epicondylar axis on the same cut. The ratios were then obtained. AP data for males and females was plotted against ML data. The data was found to approximate linear relation, permitting linear regression.

Inside AP and ML dimensions of eight popular TKR systems produced by six manufactures were obtained. The AP vs. ML plots were made as well as ratios were calculated for each system. The implants data were compared with male and female data.

A t-test was performed to demonstrate whether the AP/ML ratio was significantly different between males and females. In addition, ordinary least squares analyses were performed to establish whether the AP/ML ratios varied across different AP and ML sizes for both genders.

Conclusions: Our study demonstrated a significant difference in distal femur proportions between males and females. The variation in dimensions did not appear to be well covered by femoral implant sizes from studied seven commonly used TKA systems.

Dimensions propagation of femoral components for TKR fallowed significantly closer to males’ distal femur dimensions variation than to females’.