Ceramic anterior spinal fusion - Biologic and biomechanical comparison in a canine model

Study Design, Three types of porous ceramic bone graft substitutes were used for anterior interbody fusion in the canine thoracic spine. Objectives. To compare the biomechanical stiffness and histologic appearance of fused spinal segments using ceramic graft substitutes versus autogenous 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 evaluated: autogenous tricortical iliac crest (n = 6); hydroxyapatite ceramic (Interpore-200; n = 6); biphasic (60:40) hydroxyapatite/tricalcium phosphate 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 underwent nondestructive biomechanical testing and light microscopic histologic evaluation. Results. Biomechanical testing showed that spines from the autogenous tricortical iliac crest group were statistically significantly stiffer in flexion, extension, left and eight bending, and torsion than all ceramic groups. No differences in stiffnesses were observed among the three ceramic groups. Histologically, the autogenous tricortical iliac crest graft performed best, with osseous union at 10 of 12 interfaces. Of the ceramic grafts, hydroxyapatite/tricalcium phosphate and calcium carbonate demonstrated more consistent junction healing than the hydroxyapatite group, where four of 12 interfaces resulted in a nonunion, In the ceramic groups, a variable amount of revascularization and new bone was observed within the grafts. Conclusions. Autogenous iliac crest bone graft provides superior healing in this anterior spine fusion model. Additional investigation is needed before ceramic grafts can be considered satisfactory alternatives to anterior autogenous bone grafts.