Gender differences in the morphology of the trochlea and the distal femur.

PURPOSE: The objective of this study was to provide a morphologic description of the distal femur and to determine whether there are any gender differences in the shape that might have an important consequence for the design of a femoral component of a total knee prosthesis.

METHODS: Anthropometric data on the distal femur of 200 normal knees were obtained using two-dimensional MRI measurements. In all 18 parameters of the distal femur were measured including the anteroposterior (AP) dimension of femoral condyles, the mediolateral (ML) width of the distal femur at four levels, and the AP dimension and ML width of the trochlea. The aspect ratios between the AP and ML dimensions were calculated to determine whether there is a shape difference between genders.

RESULTS: The female distal femur is significantly smaller in all measured parameters. The mean AP/ML aspect ratio of the female distal femur is significantly larger (p<0.05) at all measured ML levels except that of the anterior edge of the anterior chamfer. The AP dimensions of both the medial and lateral trochlea were significantly greater in men (p<0.001), but AP/ML aspect ratio did not differ between genders.

CONCLUSIONS: We have found that although the female distal femur is relatively narrower (larger AP/ML aspect ratio) than the male in three of the four measured levels, there is no significant difference between genders at the level of the anterior edge of the anterior chamfer. It is at this level that it has been suggested that impingement between soft tissues and an overhanging prosthesis is most likely to be painful. Equally, there were no gender-related differences in the shape of the trochlea. These data therefore do not support the provision of narrow femoral components for TKA for women.