Tissue reactions to particles of bone-substitute materials in intraosseousand heterotopic sites in rats: discrimination of osteoinduction, osteocompatibility, and inflammation

Two rat models were used to characterize tissue-specific reactions to parti cles of bone-substitute materials: one for osteocompatibility in a healing tibial wound and the other in a heterotopic. subcutaneous Site. Small. unic ortical tibial wounds in rats healed spontaneously. beginning with the rapi d proliferation of intramedullary woven bone. That temporary bone was resor bed by osteoclasts and finally. the cortical wound was healed with lamellar bone and the medullary space was repopulated with marrow. When various par ticulate materials were implanted into fresh wounds. three types of reactio ns were observed. (1) Demineralized bone powder(DBP) and non-resorbable cal cium phosphate (nrCP) were incorporated into the reactive medullary and cor tical bone. (2) Polymethylmethacrylate (PMMA) particles were surrounded wit h a fibrous laver, but did not impair bone healing. (3) Polyethylene (PE) s hards and resorbable calcium phosphates (rCPs) were inflammatory and inhibi ted osseous repair. Subcutaneous sites showed osteoinductive, fibrotic. or inflammatory respons es to these materials. Only DBP induced endochondral osteogenesis subcutane ously. The nrCP evoked a fibrous reaction. In contrast. rCPs, PMMA. and PE shards generated inflammatory reactions with each particle being surrounded by fibrous tissue and large multinucleated giant cells. In conclusion. only DBP showed osteoinductive as well as osteocompatible pr operties. The nrCP was osteocompatible. The rCPs Stimulated various degrees of inflammatory responses. PMMA was osteocompatible and did not interfere with the bone healing process. PE was not osteocompatible and generated for eign body reactions in both sites. Use of the two sites distinguishes osteo inductive. osteocompatible. and inflammatory properties of particles of bon e-substitute materials. (C) 2001 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved.