Machine-learning derived acetabular dysplasia and cam morphology are features of severe hip osteoarthritis: findings from UK Biobank

The contribution of shape changes to hip osteoarthritis (HOA) remains unclear, as is the extent to which these vary according to HOA severity. In the present study, we used statistical shape modelling (SSM) to evaluate relationships between hip shape and HOA of different severities using UK Biobank DXA images. We performed a cross-sectional study in individuals with left hip DXA scans. Statistical shape modelling (SSM) was used to quantify hip shape. Radiographic HOA (rHOA) was classified using osteophyte size and number, and joint space narrowing. HOA outcomes ranged in severity from moderate (grade 2) or severe (grade ≥3) rHOA, hospital diagnosed HOA, and subsequent total hip replacement (THR). Confounder-adjusted logistic regression between the top ten hip shape modes (HSMs) and OA outcomes was performed. Further models adjusted for alpha angle (AA) and lateral centre-edge angle (LCEA), reflecting acetabular dysplasia and cam morphology respectively. Composite HSM figures were produced combining HSMs associated with separate OA outcomes. A total of 40,311 individuals were included (mean 63.7 years, 47.8% male), of whom 5.7% had grade 2 rHOA, 1.7% grade ≥3 rHOA, 1.3% hospital diagnosed HOA, and 0.6% underwent THR. Composite HSM figures for grade 2 rHOA revealed femoral neck widening, increased acetabular coverage, and enlarged lesser and greater trochanters. In contrast, grade ≥3 rHOA, hospital diagnosed HOA and THR were suggestive of cam morphology and reduced acetabular coverage. Associations between HSMs depicting cam morphology and reduced acetabular coverage and more severe HOA were attenuated by AA and LCEA adjustment, respectively. Relationships between hip shape and HOA differed according to severity. Notably, cam morphology and acetabular dysplasia were features of severe HOA, but unrelated to moderate disease, suggesting possible prognostic utility.