Prospective bone density changes after periacetabular osteotomy: a methodological study.

We used computed tomography (CT) and 3D design-based sampling principles (stereology) to estimate changes in acetabular bone density after periacetabular osteotomy. We included six consecutive patients with hip dysplasia in the study. Baseline density was measured within the first 7 days following periacetabular osteotomy and compared with bone density 2 years later. Double measurements were performed on three patients, and the coefficient of error of the mean was estimated to 0.05. Bone density in zone 1 increased significantly in the anteromedial quadrant as well as in the posteromedial quadrant of the acetabulum. In the anterolateral and the posterolateral quadrant, bone density was unchanged. In zone 2 and 3, bone density was unchanged 2 years postoperatively. We suggest that the observed increase in bone density medially represents a remodelling response to an altered load distribution after osteotomy. The method used is a precise tool to estimate changes in acetabular bone density.