EFFECT OF POLY DL-LACTIDE-CO-GLYCOLIDE IMPLANTS AND XENOGENEIC BONE MATRIX-DERIVED GROWTH-FACTORS ON CALVARIAL BONE REPAIR IN THE RABBIT

Polymer implant discs composed of 50:50 poly DL-lactide-co-glycolide ( molecular weight about 9000) were used to repair 5 mm calvarial defect s in 2 kg rabbits and osseous repair compared to spontaneous healing ( control). After 4 weeks the implants had undergone substantial degrada tion with little evidence of residual polymer. The extent to which the defects had been replaced by bone showed individual variation. In som e animals a layer of bone with normal cancellous architecture had brid ged the defect, but at no time was bone observed in intimate contact w ith the polymer matrix, suggesting that the material had acted as a ti ssue spacer rather than an osteoconductive substrate. Non-osseous tiss ue consisted of a highly vascular fibrous connective tissue containing variable numbers of inflammatory cells. In some sites numerous macrop hages and multinucleate giant cells were observed, the majority of whi ch were shown by immunocytochemistry to be MHC class Ii-positive. Hist omorphometric analysis demonstrated no statistically significant diffe rence in osseous repair between control and polymer implant groups aft er 1, 2 or 3 months. Incorporation of bone matrix proteins extracted f rom bovine cortical bone into the discs, however, provoked a cellular and humoral immune response which had a significant inhibitory effect on osseous repair. These data suggest, first, that while synthetic pol ymers have potential as bone graft substitutes, improvements in their performance in vivo are needed and, second, it is advisable to use all ogeneic proteins in rabbit models of bone regeneration.