Histopathology of failed osteoarticular shell allografts

Fresh cadaveric osteochondral fragment allografts were used to replace damaged articular surfaces of knee joints. Of the original 100 patients, 22 experienced graft failure necessitating graft removal. From these patients, a total of 44 osteochondral allografts were extirpated between 12 and 84 months after insertion. These were examined radiologically, histologically, and ultrastructurally. The bone and bone marrow were necrotic and had undergone variable replacement by host bone, which appeared to be independent of the duration of the graft. The articular cartilage showed degenerative changes ranging from fibrillation to erosion. Viable donor cartilage was present as late as seven years, proving that fresh graft cartilage can survive transplantation. Host bone interfaced with the cartilage, but in 14 grafts there was focal invasion of the cartilage. In some grafts, pannus formation with resorption of cartilage was evident. There was no histologic evidence of transplant rejection. This study is encouraging because hyaline cartilage has been shown to survive for as long as seven years and because bone can be replaced in a homogeneous fashion if the correct biomechanical conditions are met.