Joint changes in transplanted caudal vertebrae

Abstract

Both straight and bent segments of tails from 4-d-old and weaning Sprague-Dawley rats were used to study the changes which occur in symphyseal joints on transplantation to non-functional sites. In the joints from the younger donors ankylosis occurred almost invariably in the proximal end of the tail, while distally it was rarely seen unless the tail was curved, when ankylosis was visible on the inner side of the bend. The joints from the older donors showed a more varied response on transplantation. Some appeared unaltered, in others where growth continued, calcific changes were seen. In bent segments, unlike in younger ones, ankylosis occurred preferentially on the outer side of the bend. Histological examination revealed that ankylosis of the joint occurred through a process of chondroid metaplasia of the intervertebral connective tissue with subsequent replacement by bone. The metaplastic joint changes were primarily the results of pressure producing compression of the annulus fibrosus in tissues with a reduced vitality due to transplantation and lack of function.