The morphology of the acetabulum in prearthrosis and early coxarthrosis by pelvic CT

A thorough understanding of the hip joint is necessary for prediction and prevention of hip osteoarthritis (OA). The hip joint is commonly evaluated using X rays, arthrograms, arthroscopic findings and magnetic resonance imaging. Two-dimensional pelvic computed tomography (CT) has also been used, but its clinical relevance has not been studied sufficiently. The aim of this investigation was to evaluate the effectiveness of pelvic CT, especially during prearthrosis and early coxarthrosis, for estimation of the progression in hip OA. Acetabular sector angles were measured in normal (n=29), prearthrosis (n=81), and early coxarthrosis (n=61). The findings suggest that the posterior regions of the acetabulum deteriorate more than the anterior regions as arthritis progresses, as shown by comparing the posterior acetabular sector angle (normal, mean±SD, 102.5 deg±9.3 deg; prearthrosis, 93.3 deg±7.0 deg; early coxarthrosis, 90.9 deg±9.6 deg) with the anterior acetabular sector angle (normal, 55.5 deg±9.4 deg; prearthrosis, 49.2 deg±8.1 deg; early coxarthrosis, 50.5 deg±11.9 deg). In addition, the horizontal actabular sector angle (HASA), which shows the general size of the acetabulum, was smaller in the more arthritic hips (normal, 158.0 deg±12.9 deg, prearthrosis, 142.5 deg±10.9 deg, early coxarthrosis, 141.4 deg±17.6 deg). This suggests that a small acetabulum, and especially posterior dysplasia, may be a risk factor in the progression from normal to prearthrosis and early coxarthrosis. We propose that the posterior acetabulum plays a relatively important role in the progression of hip osteoarthritis, and that its significance for the condition has previously been underestimated. (author)