THE EFFECT OF A COMPOSITE OF POLYORTHOESTER AND DEMINERALIZED BONE ON THE HEALING OF LARGE SEGMENTAL DEFECTS OF THE RADIUS IN RATS

The effect of a composite of demineralized bone mixed with polyorthoester on the healing of large segmental defects in the rat radius was studied. Sixty male Wistar rats were divided into four groups, A through D, and an osteoperiosteal diaphyseal defect of 50 per cent of the length of the bone was made in the right radius of each rat. In Group A, the defect was filled with polyorthoester and demineralized bone; in Group B, demineralized bone; and in Group C, polyorthoester. No material was implanted in the defects in the Group-D rats. The rats were killed fifty days postoperatively. The formation of bone in the defects was quantified with computer-assisted measurements of the area on radiographs. The host-tissue response was evaluated with light microscopy. Defects that had been filled with the composite of polyorthoester and demineralized bone or with demineralized bone alone showed regeneration of bone corresponding to 93.6 and 77.6 per cent or the area of the defect, respectively. Defects that had no implant or that had been filled with polyorthoester alone showed significantly less formation of bone. No inflammation was seen with light microscopy, and only traces of the polyorthoester could be detected in the defects that had been filled with the composite or with polyorthoester alone. CLINICAL RELEVANCE: A biodegradable carrier is desirable for demineralized bone chips or powder, which otherwise are technically difficult to use because of lack of adhesion of demineralized bone particles to each other and to the surrounding tissue. In addition, as purified bone inductors and growth factors become available, a biodegradable carrier will be needed to provide sustained release of such factors. In the current study, the demineralized bone mixed rapidly with blood, forming a grainy mixture that tended to be displaced, whereas the composite implant was moldable and easy to place in the defect, and the tendency for displacement was less. The polyorthoester also provided local hemostasis when used either alone or in a composite with demineralized bone. Because the polyorthoester may provide controlled, sustained release of the incorporated active substance, it seems promising as a carrier of purified inductors and growth factors.