THE EFFECTS OF THERAPEUTIC DOSES OF IRRADIATION ON EXPERIMENTAL BONE-GRAFT INCORPORATION OVER A POROUS-COATED SEGMENTAL DEFECT ENDOPROSTHESIS

The incorporation of autogeneic bone graft into a porous coated segmen tal endoprosthesis after high-dose irradiation was studied in dogs. A mid-diaphyseal defect was surgically created and then reconstructed wi th a porous-coated segmental endoprosthesis in 16 dogs. Autogeneic bon e grafts were placed over the porous-coated regions of the endoprosthe sis and at the endoprosthesis-bone junctions to achieve extracortical fixation. In eight dogs, the reconstructed femora were treated with a time-equivalent dose of 5500 cGy, delivered over a five-week period, b eginning three weeks after surgery. In eight dogs, which served as the control group, the reconstructed femora were not irradiated. Dogs wer e killed 12 weeks after surgery, and the reconstructed femora were eva luated clinically, roentgenographically, mechanically, and histologica lly. Extracortical bone formation and bone ingrowth into the porous-co ated segmental endoprosthesis were significantly inhibited by high-dos e irradiation. Nonirradiated reconstructed femora had higher maximum t orque at the implant-bone junction than irradiated femora. Nonirradiat ed femora had significantly greater bone ingrowth within the porous sp ace than irradiated femora. Intracortically, irradiated femora had gre ater unlabeled bone and less porosity as well as more new bone than no nirradiated femora at 12 weeks postsurgery. Extracortically, irradiate d femora had greater original cortical bone and less porosity as well as more new bone than nonirradiated femora at 12 weeks postsurgery. Mi neral apposition was less in the irradiated femora from the initiation of radiotherapy to the time of killing five weeks after cessation of irradiation.