Background/Purpose:  African Americans have higher prevalence and greater severity of knee osteoarthritis (OA) on radiographs compared with Caucasians. Magnetic resonance imaging (MRI)-based quantification of 3-dimensional (3D) anatomical changes of the knees may offer superior insights into potential racial differences in joint morphology compared with radiographs. Therefore, we applied this method to examine anatomical differences between African Americans and Caucasians.

Methods:  We used data from the OAI, a longitudinal cohort study designed to investigate the natural history of and risk factors for knee OA. Active appearance modelling, which has excellent reliability, was used to automatically segment the knee MRI (MAGNETOM Trio, Siemens) sagittal 3D DESS-we sequence from each femur as principal components from a shape model. The OA bone shape vector is a line through the mean shape of a training set of OA and non-OA femurs, also expressed as principal components. Individual bone shapes are projected orthogonally onto the OA bone shape vector. Zero is defined as the mean non-OA shape, 1 unit is 1 SD of the non-OA shape distribution. Positive values indicate more of an OA shape. Separate vectors were prepared for males and females. We quantified the difference in 3D femur bone shape between African Americans and Caucasians, stratified by sex, using linear regression, adjusting for KL grade, age, and body mass index (BMI), using generalized estimating equations to account for the correlation between knees within the same subject.

Results:  We included 1534 African American and 7319 Caucasian knees that had 3D bone shape measured at baseline. Of African Americans, 481 male and 1053 female knees were assessed. Of Caucasians, 3165 male and 1053 female knees were included. In male and female knees, the crude mean 3D bone shape vectors for the distal femur were higher for African Americans compared with Caucasians, even at KL grade 0 (Table 1). Significant differences in 3D bone shape were found between in African Americans and Caucasians, stratified by sex, controlling for age and BMI (Table 2).

Conclusion:  African Americans had more overall anatomical changes of OA than Caucasians in MRI-based 3D femur bone shape, which were not due to differences in KL grade, age, or BMI. Further, African Americans had higher OA vector values, even at KL grade 0, than Caucasians, and this may explain the higher prevalence of OA in African Americans. Of note, age and BMI had only minimal effect on 3D femur bone shape change. This finding of racial differences in 3D bone shape warrants further investigation to understand the underlying mechanisms causing these differences to gain further insight into factors influencing the pathogenesis of OA.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/racial-differences-in-magnetic-resonance-image-based-three-dimensional-bone-shape-of-the-knee-data-from-the-osteoarthritis-initiative-oai/