Hip shape as a predictor of osteoarthritis progression in a prospective population cohort

OBJECTIVE: Hip morphology plays a significant role in the incidence and progression of hip osteoarthritis (OA). We hypothesized that hip shape would also associate with other key factors and tested this in a longitudinal community-based cohort combining radiographic, MRI, DXA, and clinical data.

METHODS: Baseline dual-energy X-ray absorptiometry (DXA) images of the left hip of 831 subjects from the Tasmanian Older Adult Cohort (TASOAC) were analyzed using an 85-point statistical shape model. Hip pain was assessed by WOMAC (Western Ontario and McMaster Universities Osteoarthritis Index) and muscle strength was measured by a dynamometer. Hip structural changes were assessed using MRI and Radiographic OA (ROA) using plain radiographs.

RESULTS: Six shape modes described 68% of shape variation. At baseline, modes 1, 2, 4 and 6 were associated with hip ROA, modes 1, 3, 4 and 6 correlated with hip cartilage volume and all except mode 2 with muscle strength. Higher mode 1, and lower mode 3 and 6 scores at baseline predicted hip pain at follow-up and higher mode 1 and mode 2 scores were associated with hip effusion-synovitis. Greater scores for mode 2 (decreasing acetabular coverage) and lower mode 4 (non-spherical femoral head) at baseline predicted 10-year total hip replacement (THR); while mode 4 alone correlated with bone marrow lesions (BMLs), effusion-synovitis, and increased cartilage signal.

CONCLUSIONS: Hip shape is associated with ROA, THR, hip pain, effusion-synovitis, BMLs, muscle strength and hip structural changes. These data suggest that different shape modes reflect multiple facets of hip osteoarthritis. This article is protected by copyright. All rights reserved.