Three-dimensional Morphology of the Knee Reveals Ethnic Differences

BACKGROUND: Studies have demonstrated sex differences in femoral shape and quadriceps angle raising a question of whether implant design should be sex-specific. Much of this research has addressed shape differences within the Caucasian population and little is known about differences among ethnic groups. QUESTIONS/PURPOSES: We therefore asked: Do shape differences in the distal femur and proximal tibia exist among different ethnic groups and between the sexes in each ethnic population? And if ethnic differences exist, do they have a clinical impact on current TKA design? SUBJECTS AND METHODS: We analyzed 1000 normal adult knees (80 African American, 80 East Asian, and 860 Caucasian). Three-dimensional surface models were created for each bone and added to three-dimensional statistical bone atlases. Statistical shape analysis was conducted with a process combining principal components and multiple discriminate analyses. Eleven femoral and nine tibial measurements were calculated. RESULTS: We found differences in mean measurements between the sexes and ethnicities. Males had larger knees, with a mean 5-mm-larger anteroposterior dimension than females in all ethnicities. African American females had a 7.4-mm-deeper patellar groove, 2.3-mm-smaller tibial mediolateral dimension, and 2.5-mm-larger tibial anteroposterior dimension than Caucasian females. African American males had a 4.3-mm-larger femoral anteroposterior dimension, 10.1-mm-larger tibial mediolateral dimension, and 6-mm-larger tibial anteroposterior dimension than Asian males. CONCLUSIONS: We identified differences in three-dimensional knee morphology among Caucasian, African American, and East Asian populations. Clinical studies will be required to determine whether these differences are important for implant design.