Impact of freezing on immunology and incorporation of bone allograft.

With an increasing clinical use of deep frozen allograft for bone reconstruction, it is important to understand the immunological and biological events of allograft incorporation. In this study, we have investigated the impact of deep freezing on immunology and biopotency for incorporation of bone allografts. Deep frozen bone grafts matched or mismatched for major histoscompatibilty complex (MHC) were implanted in an 8-mm segmental defect in the tibia in rats. The construct was stabilized with intramedullary nailing. The immune response was evaluated by determination of serum antibody against the grafts MHC molecules at day 1 and after 2 and 4 months. Incorporation of the graft was compared with fresh syngeneic grafts and assessed with the use of conventional radiography, biomechanical testing and measurement of bone mineral content and density after 4 months. The analyses revealed no antibody responses in the rats that received grafts from donors differing at histocompatibility loci, and at 4 months the frozen grafts showed an overall reconstruction that was not significantly different from the fresh grafts. This study indicates that in the long run there are no significant consequences; either immunological or biomechanical, of the use of deep frozen allogenous bone as compared to fresh autogenous bone grafts in this animal model.