Recently, gender-specific designs of total knee replacement have been developed to accommodate anatomical differences between males and females. We examined a group of male and female distal femora matched for age and height, to determine if there was a difference in the aspect ratio (mediolateral distance versus anteroposterior distance) and the height of the anterior flange between the genders. The Hamann-Todd Collection provided 1207 skeletally mature cadaver femora. The femoral length, the anteroposterior height, height of the lateral and medial flanges and the mediolateral width were measured in all the specimens. The mechanical axis of the femur, the cut articular width and the aspect ratio were assessed. Statistical analysis of the effect of gender upon the aspect ratio and the lateral and medial flanges was undertaken, controlling for age, height and race. The mean aspect ratio of male femora was 1.21 (SD 0.07) and of female femora it was 1.16 (SD 0.06) (p < 0.001). There was no significant difference between male and female specimens in the mean size of the lateral flange (6.57 mm (SD 2.57) and 7.02 mm (SD 2.36), respectively; p = 0.099) or of the medial flange (3.03 mm (SD 2.47) and 3.56 mm (SD 2.32), respectively; p = 0.67). Future work in the design of knee prostheses should take into account the overall variability of the anatomy of the distal femur.

Therapeutic study, Level IV-1 (case series). See the Guidelines for Authors for a complete description of levels of evidence.

Polyethylene wear and associated osteolysis are major limitations to the long-term success of total hip arthroplasty. In vitro laboratory studies suggest polyethylene wear in THA may be substantially reduced with ceramic femoral heads. We evaluated the potential value of zirconia ceramic on conventional polyethylene as an "alternative bearing" for total hip arthroplasty in a prospective, randomized clinical trial in comparison with femoral heads made of Co-Cr-Mo. Patients were evaluated with standardized clinical outcome instruments, and measurement of head penetration was performed with computerized wear measurement software. Study enrollment was halted because of a recall of the zirconia heads. At that time, 30 total hip arthroplasties with Co-Cr-Mo heads and 30 total hip arthroplasties with zirconia heads had been performed. Mean followup was similar for both groups (Co-Cr- Mo = 51.7 months; zirconia = 51.2 months). The mean annual head penetration rate was low and similar for both groups (Co-Cr-Mo = 0.060 mm/year; and zirconia = 0.055 mm/year). In view of the recently reported potential for zirconia ceramics to undergo monoclinic phase transformation in vivo, with resultant increased fracture risk and degradation of wear properties, we do not recommend use of zirconia femoral heads as an "alternative bearing" for total hip arthroplasty.