RESORBABLE CALCIUM-PHOSPHATE BONE SUBSTITUTE

The in vitro and in vivo properties of a novel, fully resorbable, apat itic calcium phosphate bone substitute (ABS) are described. The ABS wa s prepared from calcium phosphate precursors that were hydrated to for m an injectable paste that hardens endothermically at 37 degrees C to form a poorly crystalline apatitic calcium phosphate (PCA). The PCA re action product is stable in vivo as determined by FTIR and XRD analysi s of rabbit intramuscular implants of ABS retrieved 4, 7, and 14 days postimplantation. Bone formation and resorption characteristics of the ABS material were characterized in a canine femoral slot defect model . Femoral slot defects in dogs were filled with either autologous bone implants or the ABS material. Sections of femoral bone defect site fr om animals sacrificed at 3, 4, 12, 26. and 52 weeks demonstrated that new bone formation proceeded similarly in both autograft and ABS filed slots. Defects receiving either material were filled with trabecular bone in the first 3 to 4 weeks after implantation; lamellar or cortica l bone formation was well established by week 12. New bone formation i n ABS filled defects followed a time course comparable to autologous b one graft filled defects. Histomorphometric evaluation of ABS resorpti on and new bone formation indicated that the ABS material was greater than 99% resorbed within 26 weeks; residual ABS occupied 0.36 +/- 0.36 % (SEM, n = 4) of the original defect area at 26 weeks. Quantitatively and qualitatively, the autograft and ABS were associated with similar new bone growth and defect filling characteristics. (C) 1998 John Wil ey & Sons, Inc.