Acetabular changes in an experimental model of developmental dysplasia of the hip (DDH).

We wished to correlate the morphological acetabular changes in developmental dysplasia of the hip (DDH) with changes at the tissue level. A secondary aim was to develop a way of measuring the dysplastic acetabulum. We studied the changes in rabbit acetabula after maintaining knee extension, measuring the major diameter from the acetabular notch to the farthest opposite point on the acetabular margin. The minor diameter was at right angles to this. The dysplastic acetabula showed elongation along the major diameter compared to control hips. Microscopic sections were made along major and minor diameters. The posterosuperior lip of the dysplastic acetabulum showed an early eversion of the acetabular cartilage. Growth of the articular cartilage in this new direction accounted for the acetabular elongation. As well as providing insight into the manner of acetabular shape change, the findings suggest the nature of remodeling required before normal acetabular growth can resume during treatment.