BONE INDUCTION USING DEMINERALIZED BONE IN THE RABBIT FEMUR - A LONG-TERM STUDY

While traditional bone grafting is the standard for replacement of seg mental bony defects, alternative options (avoiding morbidity of autolo gous grafts) are attractive and continue to be sought. This study atte mpted to determine whether demineralized bone powder could be used rel iably to replace a significant bony deficit at a weight-bearing site. The long-term functional characteristics of this induced bone were ana lyzed to determine whether it maintained its strength and shape and re acted normally to physiologic stress over an extended period of time ( 12 months). In 55 New Zealand White rabbits, a 1-cm length of femur wa s removed (approximately 20 percent of the total length of the rabbit femur). The femur was then reconstructed with a titanium mandibular pl ate, leaving the Sap intact. In 38 of the animals, this gap was filled with demineralized bone powder in an attempt to induce bone to form a cross the defect. In group 1 (n = 23), the mandibular plate remained i n place for the duration of the study (12 months). Tn group 2 (n = 15) , the plate was removed 8 weeks after placement of the demineralized b one powder, and the animals were followed for an additional 12 months. In group 3 (n = 10), nothing was placed within the bony gap. In group 4 (n = 7), the gap was repaired. With autologous bone graft. All the animals that received demineralized bone powder completely filled the osteotomy gap with new bone within 6 to 8 weeks after implantation. No ne of control group 3 formed bone across the gap (p < 0.001). Eighty-s ix percent of control group 4 tautologous bone graft) successfully for med bone across the osteotomy gap. In addition, 90 percent of control group 3 had hardware failure within 8 weeks after surgery compared wit h 0 percent (0 of 38) of the group that received demineralized bone po wder (P < 0.001). In group I, analysis after 12 months revealed that t he bone mo formed ultimately became thin and easily fractured, most li kely because of shielding from stress loading by the mandibular plate. In contrast, in group 2 (in which the plate was removed after 8 weeks ), the bone remodeled and hypertrophied in response to the physiologic stress of weight bearing and at the end of the 12-month period was es sentially identical to normal femur. In certain circumstances, reconst ruction of bony defects using bone-induction techniques may be as good as autologous bone grafting, with the advantage of limiting the donor -site morbidity for the patient.