CERAMIC ANTERIOR SPINAL-FUSION - BIOLOGIC AND BIOMECHANICAL COMPARISON IN A CANINE MODEL

Study Design, Three types of porous ceramic bone graft substitutes wer e used for anterior interbody fusion in the canine thoracic spine. Obj ectives. To compare the biomechanical stiffness and histologic appeara nce of fused spinal segments using ceramic graft substitutes versus au togenous bone graft. Summary of Background Data. The relative success or failure of ceramic grafts is influenced by many variables including the composition of the ceramic, location in the spine, stability, and the animal model used. Methods. Four experimental groups were evaluat ed: autogenous tricortical iliac crest (n = 6); hydroxyapatite ceramic (Interpore-200; n = 6); biphasic (60:40) hydroxyapatite/tricalcium ph osphate ceramic (Zimmer; n = 4); and calcium carbonate ceramic (Inoteb ; n = 4). All dogs were killed 8 weeks after surgery. After postmortem removal of anterior spinal instrumentation, the spinal segments under went nondestructive biomechanical testing and light microscopic histol ogic evaluation. Results. Biomechanical testing showed that spines fro m the autogenous tricortical iliac crest group were statistically sign ificantly stiffer in flexion, extension, left and eight bending, and t orsion than all ceramic groups. No differences in stiffnesses were obs erved among the three ceramic groups. Histologically, the autogenous t ricortical iliac crest graft performed best, with osseous union at 10 of 12 interfaces. Of the ceramic grafts, hydroxyapatite/tricalcium pho sphate and calcium carbonate demonstrated more consistent junction hea ling than the hydroxyapatite group, where four of 12 interfaces result ed in a nonunion, In the ceramic groups, a variable amount of revascul arization and new bone was observed within the grafts. Conclusions. Au togenous iliac crest bone graft provides superior healing in this ante rior spine fusion model. Additional investigation is needed before cer amic grafts can be considered satisfactory alternatives to anterior au togenous bone grafts.