The long-term fate of fresh and frozen orthotopic bone allografts in genetically defined rats.

Fresh and frozen orthotopic iliac crest bone grafts in rats were studied histologically for determination of the long-term effects of histocompatibility matching and the freezing process on orthotopic bone graft incorporation. Grafts exchanged between groups of inbred rats, syngeneic or differing with respect to major or minor histocompatibility loci, were studied histologically at 20, 30, 40, 50, and 150 days after bone transplantation. A numerical histologic scoring system was developed and used by three observers for evaluation of coded hematoxylin and eosin sections. All frozen graft groups had the same fate regardless of histocompatibility relations between donors and recipients, and all grafts were inferior to fresh syngeneic grafts. Both fresh allograft groups received similar scores and initially at 20 and 30 days had scores similar to those of the fresh syngeneic groups. In the later intervals, however, the fresh allografts were inferior to the fresh syngeneic grafts and similar to the frozen groups. This is consistent with an older model describing two distinct phases of osteogenesis. In the long term, frozen syngeneic and fresh and frozen allografts across major and minor histocompatibility barriers were comparable, but all were significantly inferior to fresh syngeneic bone grafts.