INFLUENCE OF LOCAL ENVIRONMENT ON INCORPORATION OF CERAMIC FOR LUMBARFUSION - COMPARISON OF LAMINAR AND INTERTRANSVERSE SITES IN A CANINE MODEL

Objectives. To evaluate bone growth into macroporous ceramic in a cani ne model in terms of the effect at the lumbar spine site (lamina versu s transverse process site) and the depth of the area within the cerami c block (peripheral or central areas). Summary of Background Data. Pre vious comparative studies have assessed that the efficacy of bone graf t substitutes for spine fusion depends on their physicochemical proper ties and on the mechanical environment but rarely on the grafting site at the lumbar spine level. Methods. Posterior and lateral arthrodesis using pedicular instrumentation was performed at L2, L3, and L4 with a parallelepipedic ceramic block in an experimental group of dogs. A s econd group of dogs was fused with only autogenous bone graft to compa re the fusion stiffness obtained with this material with the stiffness obtained with ceramic. Dogs were studied for 9 months. A biomechanica l test and histomorphometric analysis were conducted. Results. With th e biomechanical test, no significant differences were found between ce ramic and autogenous bone. The percentage of newly formed bone was hig her (P < 0.0001) at the lamina (26.52 +/- 6.45%) than at the transvers e process site (17.33 +/- 2.54%). For both locations, the highest amou nt of newly formed bone was observed in the area of close contact betw een ceramic and bone, and the lowest was observed in central areas (24 .6 +/- 5.9% for the laminar site, 14.79 +/- 1.75% for the transverse p rocess site). Conclusion. This animal study, which replicated the huma n procedure in posterolateral lumbar fusion, showed a significant diff erence of ceramic incorporation between laminar and intertransverse si tes. This histomorphometric analysis also confirmed the relationship b etween bone in-growth and ceramic thickness and ceramic contact area w ith bone.