[Experimental hip dysplasia in the rabbit]

Neglected cases of congenital dislocation of the hip (CDH) always present with profoundly interesting X rays and pathoanatomical changes. Because of progressive dysplastic change, it is difficult to determine clinically at what stage a patient can not have reconstructive surgery. We used an animal model to induce hip dysplasia in order to understand the mechanism of dislocation and to demonstrate the dysplastic changes at various ages of dislocation. We used a plastic tube to immobilize the left knee of one week old New Zealand white rabbits in the extension position. Fifty-five rabbits in a natural history group were examined physically, radiographically and pathologically every month, until five months old. Ten rabbits were also studied by computed tomography before sacrifice. Forty-two rabbits which had been immobilized for more than 2 months were selected to determine the changes in their left hips. Tenotomy of the hamstrings of the left knee was performed in another 20 rabbits, which were then immobilized in the same way until 2 months old. The changes in their left hips were also determined and compared with the changes of former group. In our study, immobilization of the left knee of rabbits can induce dislocation, subluxation or no change. Tenotomy of the hamstrings can decrease the incidence of dislocation and subluxation, but cannot avoid their occurrence. In long-term observation of rabbits with dislocation and subluxation, we found that there are more dysplastic and degenerative changes in older rabbits. Computed tomography proved to be an effective evaluation tool of the size of dysplastic acetabulum and femoral head.