The effects of processing and low dose irradiation on cortical bone grafts

The authors studied the effects of standard processing and preprocessing low dose gamma irradiation (1.5 Mrad) on the strength and incorporation of syngeneic and allogeneic cortical bone grafts. Bilateral femoral middiaphyseal 8-mm segmental defects in 120 male Fisher rats were stabilized with internal fixation. Each defect received one of six types of grafts: fresh syngeneic, processed syngeneic, irradiated processed syngeneic, fresh allogeneic, processed allogeneic, and irradiated processed allogeneic grafts. Graft processing included soaking in 70% ethanol and deep freezing for preservation. Irradiation was performed by 60Co source immediately before processing. Grafts were evaluated by histologic analysis, histomorphometric analysis, and biomechanical testing at 4 and 6 months after surgery. Graft treatment, either processing or irradiation processing, did not affect consistently or significantly the incorporation of syngeneic or allogeneic grafts. Graft allogenicity was the major determinant of the revascularization and the histologic pattern of graft incorporation. Processed and irradiated processed allogeneic grafts gained compressive strength with time and were as strong as syngeneic grafts at 6 months. Biomechanical and histologic data from this study suggest that standard processing and preprocessing low dose irradiation do not compromise the natural course of allogeneic cortical bone graft incorporation.