Hip morphology plays a significant role in the incidence and progression of hip osteoarthritis (OA). We hypothesized that hip shape would also be associated with other key factors and tested this in a longitudinal community-based cohort combining radiographic, magnetic resonance imaging (MRI), dual-energy x-ray absorptiometry (DXA), and clinical data.
Baseline DXA images of the left hip of 831 subjects from the Tasmanian Older Adult Cohort were analyzed using an 85-point statistical shape model. Hip pain was assessed using the Western Ontario and McMaster Universities Osteoarthritis Index, and muscle strength was measured using a dynamometer. Hip structural changes were assessed using MRI and radiographic OA using plain radiographs.
Six shape modes accounted for 68% of shape variation. At baseline, modes 1, 2, 4, and 6 were associated with radiographic hip OA; modes 1, 3, 4, and 6 were correlated with hip cartilage volume; and all except mode 2 were correlated with muscle strength. Higher mode 1 and lower mode 3 and mode 6 scores at baseline predicted hip pain at followup and higher mode 1 and mode 2 scores were associated with hip effusion-synovitis. Higher scores for mode 2 (decreasing acetabular coverage) and lower scores for mode 4 (nonspherical femoral head) at baseline predicted 10-year total hip replacement (THR), while mode 4 alone was correlated with bone marrow lesions (BMLs), effusion-synovitis, and increased cartilage signal.
Hip shape is associated with radiographic OA, THR, hip pain, effusion-synovitis, BMLs, muscle strength, and hip structural changes. These data suggest that different shape modes reflect multiple facets of hip OA.