Influence of local environment on incorporation of ceramic for lumbar fusion - Comparison of laminar and intertransverse sites in a canine model

Objectives. To evaluate bone growth into macroporous ceramic in a canine model in terms of the effect at the lumbar spine site (lamina versus transverse process site) and the depth of the area within the ceramic block (peripheral or central areas). Summary of Background Data. Previous comparative studies have assessed that the efficacy of bone graft substitutes for spine fusion depends on their physicochemical properties 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 second group of dogs was fused with only autogenous bone graft to compare the fusion stiffness obtained with this material with the stiffness obtained with ceramic. Dogs were studied for 9 months. A biomechanical test and histomorphometric analysis were conducted. Results. With the biomechanical test, no significant differences were found between ceramic and autogenous bone. The percentage of newly formed bone was higher (P < 0.0001) at the lamina (26.52 +/- 6.45%) than at the transverse process site (17.33 +/- 2.54%). For both locations, the highest amount of newly formed bone was observed in the area of close contact between 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 process site). Conclusion. This animal study, which replicated the human procedure in posterolateral lumbar fusion, showed a significant difference of ceramic incorporation between laminar and intertransverse sites. This histomorphometric analysis also confirmed the relationship between bone in-growth and ceramic thickness and ceramic contact area with bone.