[Changes of the acetabular cartilage following experimental subluxation of the hip joint in rabbits].

Subluxation of hip joints and subsequent acetabular dysplasia was experimentally produced by fixation of young rabbits' knee joints at each extension position. The restoration of processes of acetabulum after the reduction of subluxation of one-week-fixed group (Group I) and of two-week-fixed one (Group II) were followed up. The difference in time course of the processes were discussed roentgenographically, histologically and autoradiographically using 35S. The results are as follows; Roentgenologically, acetabular angles of Group I were restored in two weeks after the removal of the wires. However, acetabular dysplasia of Group II persisted at four weeks and even six weeks after the removal of the wires. Histologically, a remarkable change of growth cartilage was observed in each hypertrophic zone of the two groups when the wires were removed. Normalization of histological changes required two weeks in case of Group I and four weeks in that of Group II. In autoradiograms using Na2 35SO4, acetabulum was normalized in four weeks after the reduction of subluxation in both groups. However, the two restoration processes showed a different pattern from each other. Judging from the above results, it is assumed that a restricted unusual stress on an acetabulum causes some morphological and functional lesion to growth cartilage more quickly than expected and that the lesion becomes more unrestorable the more the period of the stress is prolonged.