The patho-aetiology of hip osteoarthritis

Osteoarthritis of the hip frequently occurs in the absence of osteoarthritis in other large joints, suggesting that local factors are important in its pathogenesis. Hip morphology has been recognised as a potential local biomechanical risk factor for the development of hip osteoarthritis. There are no adequate studies examining osteoarthritis development in the hip. Historical cohorts are either limited by a short follow up or by small numbers. This thesis explores the natural history of hip osteoarthritis in a large population cohort with particular attention to hip morphology as a predictor of osteoarthritis development. Software was developed which allows objective measurements of hip morphology in a reproducible manner. Hip morphology was then measured in a 1000 subject cohort. A detailed description of hip morphology is presented in this thesis, with interesting observations of wide variation and a bimodal distribution for alpha angle (a measure of cam-type femoroacetabular impingement). This is suggestive of a discrete pathological entity, which was associated with osteoarthritis in the cross-sectional analysis. No significant changes exist in terms of morphology during the course of the study and no significant relationship exists between age and hip morphology. Longitudinal analysis of hip morphology with radiographic osteoarthritis and total hip replacement revealed a significant association between cam-type femoroacetabular impingement and acetabular dysplasia with both outcome measures. Measurements of hip morphology were independently predictive of outcome when controlling for baseline age, BMI and joint space width, and significantly increased our ability to predict osteoarthritis and total hip replacement. Similar associations were seen when considering hip pain and symptomatic osteoarthritis as the outcome measures of interest. Pincer-type femoroacetabular impingement was not significantly associated with any of the outcome measures of interest and pain remains relatively poorly explained by both hip morphology and/or radiographic change. The understanding of hip morphology and its role in the natural history of osteoarthritis is significantly improved by this research. Further research is now required to determine whether these morphological abnormalities represent modifiable risk factors for osteoarthritis progression.