Geometric morphometric analysis reveals ethnic group related differences in the distal femur

Abstract

A better grasp of knee morphology and its variations can improve the design of TKA implants. The same kind of implants is not suitable for different populations. The design of total knee arthroplasty implants is based on the anatomy of a Caucasian population. The purpose of this study is to show that differences in distal femur shape related to ethnic group could be identified, visualized, and quantified using three-dimensional (3D) geometric morphometric analysis. Geometric morphometric analysis was carried out on CT scans of the distal femur of 482 subjects living in the south of, France (240) and in the south of China (242). Ten landmarks were defined on 3D reconstructions of the distal femur. Both traditional metric (BCB Bicondylar breath) and geometric morphometric analyses were carried out on these bone reconstructions. The descriptive analysis consisted of calculating the mean, median and standard deviation values for each subgroup. A comparative analysis was performed with all the variables based on ethnic group and sex. The landmark coordinates were analyzed using principal component analysis (PCA) and canonical variate analysis (CVA) to identify shape trends in the various subgroups. These analyses were used to identify trends in bone shape in various subgroups: Asian, European, Asian female, Asian male, European female and European male. The osteometric analysis revealed no significant differences between the four subgroups of subjects. Ethnic-related differences in shape were statistically significant. PCA identified a difference in distal femur shape between Asians and Europeans; PC1 and PC2 accounted for 62% of the variance measured. Moreover, PCA identified a difference in distal femur shape between Asian females, Asian males, European females and European males; PC1 and PC2 accounted for 62% of the variance measured. The CVA revealed that the correct ethnic group was assigned in 82,5% of cases and the cross-validation revealed a 72,5% rate of correct sex estimation. This reliable, accurate method could be used to perform diachronic and interethnic comparisons. Moreover, this study provides updated morphometric data for a modern population in the south of France and a modern population in the south of China. The large number of subjects studied made it possible to modernize the references for certain bone measurements and should be taken into account by orthopedic implant manufacturers. This study has shown that geometric morphometric analysis of the distal femur is feasible. Ethnic-related differences are present in this bone segment.