THE EFFECT OF OSTEOGENIN (A BONE MORPHOGENETIC PROTEIN) ON THE FORMATION OF BONE IN ORTHOTOPIC SEGMENTAL DEFECTS IN RATS

We studied the effects of partially purified, natural osteogenin, a bo ne morphogenetic protein, on the formation of bone in rats. An osteope riosteal segmental defect, eight millimeters wide, in the middle of th e femoral diaphysis was created bilaterally in thirty-six adult male F ischer rats and stabilized with a polyacetyl plate and threaded Kirsch ner wires. One defect was filled with a cylinder of 60 per cent hydrox yapatite and 40 per cent tricalcium phosphate ceramic (pore diameter, 250 to 400 micrometers) containing 100 micrograms of partially purifie d bovine osteogenin, and the contralateral defect was filled with a hy droxyapatite-tricalcium ceramic cylinder without osteogenin. Eighteen animals (six animals each at one, two, and four months after the opera tion) were studied histologically and histomorphometrically. The impla nts from eighteen additional animals (six animals each at one, two, an d four months after the operation) were subjected to biomechanical tes ting. Histomorphometry revealed that the total area of bone, the area of bone outside of the implant, and the amount of bone within the pore s of the implant were all significantly (p less than or equal to 0.05) greater in the femora that had an implant with osteogenin than in tho se that had an implant without osteogenin at most time-periods. The pr esence of osteogenin had no significant effect on the biomechanical pa rameters measured in this study. CLINICAL RELEVANCE: Bone loss due to trauma, excision of a tumor, or loosening and subsidence of a joint pr osthesis is a major clinical problem. Although bone has a remarkable p otential for regeneration, predictable augmentation of the natural rep air process would be useful in certain orthopaedic situations. Particu larly attractive would be the augmentation of bone repair without the need for a cancellous autogenous bone graft, which necessitates a seco nd operative procedure. In this study, an osteogenin-containing cerami c cylinder significantly (p less than or equal to 0.005) enhanced the formation of bone in and around a large segmental defect. This enhance d repair occurred without the addition of cancellous autogenous bone g raft or marrow cells and suggests that osteogenin may be useful in the repair of skeletal defects and that this ceramic configuration may be a useful carrier of osteogenin.