ABSTRACT
Objective To explore the influence of abnormal mechanical stress on acetabular development, especially on the chondrocyte proliferation in acetabular growth plate, and to research the methods of the repair of acetabular dysplasia. Methods 60 Wistar rats of 3 weeks old were divided into three groups, and each group had twenty rats. The left side was experimental side, and the right side was control. In group A, the hip joint was dislocated by manipulation repeatedly within two weeks; in group B, the model of acetabular dysplasia was created by keeping the knee joint in extension through steel needle fixation. The needle was removed after two weeks of fixation; and in group C, the knee joint was fixed in continuous extension with steel needle. When at 5, 7, 9 and 12 weeks old, the rat acetabulum was observed through the soft X-ray photograph, histological method and electronic micrograph respectively. Results In group A, when the rat was 5 weeks old, the acetabular angle was larger roughly 5? than the control side. Malalignment of chondrocyte column in proliferative zone was observed. No difference was seen between the two sides at 7, 9 and 12 weeks old. In group B, when the rats was 5 weeks old, the acetabular angle increased compared to the control side. When the rat was 7 weeks old, malalignment of the chondrocyte column in proliferative and hypertrophic zone increased. When at 9 and 12 weeks old, histological changes became indistinct gradually. In group C, the acetabular angle kept increasing to the control side. The acetabular dysplasia became obvious and had no improving tendency. When the rat was 12 weeks old, the acetabular edge became adducting and flat. There was no obvious alignment of chondrocyte column. The nucleus of acetabular chondrocyte of the proliferative zone became smaller, endoplasmic reticulum and mitochondria decreased, and bubbles formed. Conclusion Acetabular dysplasia could recover when abnormal mechanical stress was released, and the congruence of the head and acetabulum were corrected in the highly growing period of acetabulum. The crucial reason to acetabular dysplasia is the metabolic changes of chondrocytes in proliferative zone of growth plate, which leads to tardy ossification of the acetabulum.