Bioresorbable bone graft substitutes of different osteoconductivities: a histologic evaluation of osteointegration of poly(propylene glycol-co-fumaric acid)-based cement implants in rats

Bioresorbable bone graft substitutes may significantly reduce the disadvant ages associated with autografts, allografts and other synthetic materials c urrently used in bone graft procedures. We investigated the biocompatibilit y and osteointegration of a bioresorbable bone graft substitute made from t he unsaturated polyester poly(propylene-glycol-co-fumaric acid), or simply poly(propylene fumarate), PPF, which is crosslinked in the presence of solu ble and insoluble calcium filler salts. Four sets of animals each having th ree groups of 8 were evaluated by grouting bone graft substitutes of varyin g compositions into 3-mm holes that were made into the anteromedial tibial metaphysis of rats. Four different formulations varying as to the type of s oluble salt filler employed were used: set 1-calcium acetate, set 2-calcium gluconate, set 3-calcium propionate, and set 4-control with hydroxapatite, HA, only. Animals of each of the three sets were sacrificed in groups of 8 at postoperative week 1, 3, and 7. Histologic analysis revealed that in vi vo biocompatibility and osteointegration of bone graft substitutes was opti mal when calcium acetate was employed as a soluble salt filler. Other formu lations demonstrated implant surface erosion and disintegration which was u ltimately accompanied by an inflammatory response. This study suggested tha t PPF-based bone graft substitutes can be designed to provide an osteocondu ctive pathway by which bone will grow in faster because of its capacity to develop controlled porosities in vivo. Immediate applicability of this bone graft substitute, the porosity of which can be tailored for the reconstruc tion of defects of varying size and quality of the recipient bed, is to def ects caused by surgical debridement of infections, previous surgery, tumor removal, trauma, implant revisions and joint fusion. Clinical implications of the relation between developing porosity, resulting osteoconduction, and bone repair in vivo are discussed. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.