Abstract
Background
Recent anthropometric studies have suggested that current design of total knee arthroplasty (TKA) does not cater to racial anthropometric differences. The purpose of this study was to investigate the exact sizing and rotational landmarks of the distal femur collected and its gender differences from a large group of healthy Southern Chinese using 3D-CT measurements, and then compare these measurements to the five total knee prostheses conventionally used in China.
Methods
This study evaluated distal femoral geometry in 85 healthy Southern Chinese, included 39 females (78 knees) and 46 males (92 knees) with a mean age of 33.9 years，a mean height of 164.7 cm and a mean weight of 59.9 kg. The width of the articular surface as projected onto the transepicondylar line(ML), anteroposterior dimension (AP), the dimensions from medial/lateral epicondyle to posterior condylar (MEP/LEP) were measured. A characterization of the aspect ratio (ML/AP) was made for distal femur. The angles between the tangent line of the posterior condylar surfaces, the Whiteside line, the transepicondylar line, and the trochlear line were measured. The sulcus angle and hip center-femoral shaft angle were also measured [Fig. 1]. The data were compared with the five total knee prostheses conventionally used in China. In analyzing the data, best-fit lines were calculated with use of least-squares regression. The dimensions are summarized as the mean and standard deviation. Comparisons of dimensions between males and females were made with use of the two-sample t test. A p value of <0.05 indicated a significant effect.
Results
Within the population, males had larger ML, AP values and aspect ratio than females (ML: 70.44±3.04 vs. 61.40±2.62 mm, P<0.001; AP: 62.26±2.93 vs. 56.49±2.88 mm, P<0.001; 1.06±0.05 vs. 1.11±0.03, P<0.001). In addition, we found a gradual decrease in the aspect ratio corresponding to an increase in AP dimension, as seen in other studies. The transepicondylar axis was a reliable landmark to properly rotate the femoral component, so we used the MEP and LEP evaluate posterior condylar offset, the values were respectively 28.90±3.00 mm and 22.73±2.67 mm. However, most angles were almost the same between males and females. To evaluate the suitability shape of the femoral components currently used in China, we drawed and calculated best-fit lines for the AP, ML dimensions and aspect ratios of the femur and the five prostheses. For females, there was a significant association between the prostheses size and the amount of overhang, the femoral prostheses for females tended to be too large for a given AP dimension, with larger sizes having more overhang, especially in ML dimensions. In males, the morphologic data tended to be bigger than the prosthetic designs in the ML dimension for a given AP dimension, the femoral aspect ratio was higher for smaller knees and proportionally lower for larger knees[Fig. 2, 3].
Conclusion
Because dimensions of the distal femur and the aspect ratio tend to be smaller in Southern Chinese populations, whereas sulcus angles tend to be larger, designs for knee implants should be modified to improve the outcome of surgical treatment in this population.
