Freeze-dried segmental fibular allografts in azathioprine-treated dogs.

The successful use of a bone allograft may be negated by the host's immune response. This investigation assessed the efficacy of combining freeze-dried cortical allografts in three to six weeks azathioprine-immunosuppressed dogs. Forty-eight of 94 adult mongrel dogs were initiated for this study, and 46 of 94 were previously published and recompiled. The dogs were divided into five groups and followed for six months: Group I consisted of bilateral fresh autografts as an external control; Group II assessed the effect of freeze-drying on autogenous bone; Group III compared fresh autografts with fresh allografts; Group IV assessed the effect of freeze-drying on allografts; and Group V assessed the combined effect of placing freeze-dried allografts in immunosuppressed hosts. Biweekly roentgenograms were made to evaluate the time to union and the incidence of graft fatigue failure. Mechanical graft strength was assessed by rapid torsional loading to failure at the time of sacrifice. Biologic repair was assessed with the use of tetracycline and microradiographic techniques. The incorporation and repair of a fresh cortical autograft is better than that of a freeze-dried autograft because of fractures, nonunion, or delayed union of graft-host junctions; freeze-dried autografts have increased peripheral and internal resorption, yet an increased peripheral bony callus maintains normal graft strength; freeze-dried and fresh allografts are similar in roentgenographic characteristics, mechanical strength, and in the mechanism of graft incorporation; the use of three or six weeks azathioprine therapy did not improve the fate of freeze-dried allografts.