[Bone dynamics of the acetabulum in experimental subluxation of the hip joint and its repair process]

Subluxation of the hip and subsequent acetabular dysplasia were experimentally produced by fixing the knee of young rabbits in extension position. Changes of the acetabulum during the repair process after reduction were investigated radiologically, histologically and histomorphometrically. Radiologically, subluxation and acetabular dysplasia appeared two weeks after fixation and disappeared as the knee became flexible after removal of fixation. Histologically, abnormalities of growth cartilage and hypertrophy of trabeculae in the secondary spongiosa were prominent two weeks after fixation. Histomorphometrically, the bone area, osteoid surface and mineral appositional rate increased at this time. The above findings, however, were normalized as concentric reduction of the hip was achieved. Abnormal stress acting on the acetabulum caused hypertrophy of trabeculae, and this may result in the development of osteoarthritis. In order to prevent such a pathologic process, it is important to normalize the hip mechanically from the view point of bone dynamics.