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 from a large group of healthy Southern Chinese using three dimensional computer tomographic measurements, and then compare these measurements to the known dimensions from Caucasian populations.
Methods
This study evaluated distal femoral geometry in 125 healthy Southern Chinese, included 58 women (106 knees) and 67 men (134 knees) with a mean age of 35.2±8.11 years, a mean height of 165.5±7.94 cm, and a mean weight of 61.7±9.56 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[Fig. 1]. 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. Known dimensions from Caucasian populations were compared with the morphologic data collected in this study[Fig. 2]. 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. The differences of rotational landmarks and sizing between the Southern Chinese and Caucasians were assessed with use of the Student t test. A p value of <0.05 indicated a significant effect.
Results
Within the Southern Chineses population, males had larger ML and AP values than females (ML: 70.38±3.09 vs. 62.09±2.52mm, P<0.001; AP: 63.68±2.82 vs. 57.83±2.91mm, P<0.001). The results also showed that Southern Chinese knees were generally smaller than Caucasian (ML: 67.27±4.95 vs. 76.8±7.2mm, P<0.001). The femoral aspect ratio of Southern Chinese was significantly smaller than Caucasian (1.09±0.04 vs. 1.28±0.06, P<0.001). In addition, we found a gradual decrease in the aspect ratio corresponding to an increase in anteroposterior dimension in the distal femur of Southern Chinese, as seen in most other studies. The transepicondylar axis was found to be a reliable landmark to properly rotate the femoral component, so we used the femoral condylar MEP and LEP evaluate posterior condylar offset, the values were respectively 28.62±2.18mm and 22.50±2.19mm. From this study, most of the angles were different from Caucasian. Anteroposterior line minus epicondylar line angle was 90.14±1.30° (Caucasian 90.33±2.44°, P>0.05), anteroposterior line minus posterior condylar line angle was 83.18±1.94° (Caucasian 86.82±2.71°, P<0.001), epicondylar line minus posterior condylar line angle was 7.00±1.70° (Caucasian 3.60±2.02°, P<0.001), trochleoepicondylar angle was 12.45±2.34°(Caucasian 4.95±2.15°, P<0.001), sulcus angle was 147.40±4.69° (Caucasian 139.6±6.96°, P<0.001). The angle between mechanical and anatomic axis of the femur was 5.92±0.47°(Caucasian 6.33±2.42°, P<0.001).
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. The Larger epicondylar line minus posterior condylar line angles, and the smaller angle between mechanical and anatomic axis seen in Southern Chinese populations also requires us to pay particular attention to surgical technique, in order to ensure patient safety.
