A shallow hip socket predicts osteoarthritis of the hip

Long-term study suggests moderate acetabular dysplasia, a developmental condition of hip instability, as an independent risk factor for the disease.

Osteoarthritis (OA) of the hip is one of the leading causes of disability among elderly men and women. This progressive joint disease involves multiple factors, including genes, age, gender, hormones, as well as body mass index, mechanical stress. In addition, a developmental condition known as acetabular dysplasia can contribute to disease risk. Often present at birth, acetabular dysplasia is marked by a shallow hip socket, making the hip unstable and, in extreme cases, prone to dislocation. Severe acetabular dysplasia has been linked to premature hip OA. The influence of moderate acetabular dysplasia on the development of hip OA is less clear. To assess the role of moderate acetabular dysplasia in the onset of hip OA, a research team in the Netherlands conducted a long-term study on 835 women and men ages 55 years and older. Their results, published in the March 2005 issue of Arthritis & Rheumatism, indicate acetabular dysplasia, even when assessed at a mild degree, as a strong independent risk factor for OA of the hip, even in an elderly population.

Led by Dr. M Reijman and supported by the Dutch Arthritis Association, the research team drew its subjects from The Rotterdam Study, a comprehensive investigation of the incidence of, and risk factors for, chronic disabling diseases. At baseline, the participants had no signs of radiographic OA of the hip. Women comprised 57 percent of the sample, whose mean age was 65 years. At baseline, all participants underwent radiographs in order to detect the presence and assess the depth and degree, using the center- edge angle, of acetabular dysplasia. Participants were also evaluated for current BMI and history of heavy, physically demanding work.

Over a follow-up period averaging six years, participants were examined, through radiographs, for definite signs – osteophytes and joint space narrowing – of hip OA. Calculating odds ratios, subjects with acetabular dysplasia, from moderate to mild, had a 4.3 times increased risk for radiographic OA of the hip. Among subjects with acetabular dysplasia, the incidence and severity of hip OA was greater among women, as well as associated with a high- stress mechanical workload and a low BMI. Based on this study's findings, Dr. Reijman concludes that acetabular dysplasia, at any measurable depth or degree, is a strong, independent indicator for the development of OA of the hip. "Furthermore," he notes, "the associations between acetabular dysplasia and incident radiographic OA of the hip may even be underestimated because of the relatively high mean age of the study population. In other words, we assume that in a younger population the association between acetabular dysplasia and OA may be even higher."