Abstract
[Objective]
The objectives of this study are to measure the morphometric parameters of pre-operative distal femur in Japanese patients who received TKA, to investigate the differences in distal femoral anatomy between the genders, and to compare the measurements with the dimensions of femoral implants current used in Japan.
[Methods]
One-hundred seventy-nine Japanese patients who underwent TKA in Osaka Koseinenkin Hospital from April, 2009 to December, 2011 were included in this study. The genders and diagnoses were 25/ 154 patients (male/ female) and 143/ 36 patients [osteoarthritis (OA)/ rheumatoid arthritis (RA)], respectively. The mean age, height and body weight were 73.2 years, 152.2 cm and 56.7 kg, respectively. We measured the AP length, ML width, aspect ratio angle of distal femur. The measurement points on the medial condyle was 10 mm and on the lateral condyle was 8 mm from the lowest points of the medial and lateral posterior condyle to stimulate the optimal cutting thickness. We evaluated the relationship between AP length and ML width, or aspect ratio and ML width in diagnosis, alignment and gender. We also compared the measurements with the dimensions of femoral implants current used in Japan.
Continuous variables were assessed using the Mann-Whitney's U test. Relationship between AP length and ML width, or aspect ratio and ML width were assessed using simple regression analysis. Regression lines were assessed using analysis of covariance. For all tests, probability values (p values) of < 0.05 were considered to indicate statistical significance.
[Results]
The mean AP length, ML width, aspect ratio, SEA/PCA angle and Whiteside/SEA angle were 58.8 mm, 64.7 mm, 0.91, 3.5 degrees of external rotation and 1.6 degrees of external rotation, respectively. The both relationship between AP length and ML width, and aspect ratio and ML width were significant (p < 0.001). As the ML width was getting longer, AP length was getting shorter and aspect ratio was getting lower. Although analysis of covariance between OA and RA in the relationship between aspect ratio and ML width was not significant (p = 0.955), that of valgus alignment [femorotibial angle (FTA) < 170 degrees] and varus alignment (FTA > 176 degrees) were significant (p = 0.003). The AP length, ML width in male (63.6 mm, 72.7 mm) were longer than those in female (58.1 mm, 63.4 mm), and aspect ratio in male (0.88) were lower than that in female (0.92) significantly (all p < 0.001). Although analysis of covariance between male and female in the relationship between AP length and ML width, and aspect ratio and ML width were not significant (p = 0.985 and 0.555).
[Conclusion]
The aspect ratio showed a higher ratio for smaller knees and a proportionally lower ratio for lager knees in Japanese. The tendency of aspect ratio change with ML width was different between valgus and varus alignment. As the tendency of aspect ratio change with ML width was not different between male and female, the gender difference of aspect ratio was related to the difference of skeleton size (ML width) between male and female.
