Wednesday, September 26, 2018 7:35 AM–9:00 AM ePosters

Abstract

BACKGROUND CONTEXT Posterolateral lumbar arthrodesis by autologous bone graft is a commonly performed procedure for the treatment of degenerative spine conditions. However, because autograft is associated with considerable disadvantages (eg, donor-site morbidity), alternative technologies are under investigation. Calcium phosphates (CaP) with submicron-scale surface topography have attracted attention due to their excellent performance in regeneration of bone defects. PURPOSE Evaluating the efficacy of a biphasic calcium phosphate (BCP) ceramic with a novel surface topography of submicron-scale epitaxial polygon crystals as autograft extender in the “Boden” rabbit posterolateral spine fusion model. STUDY DESIGN/SETTING BCP granules with the submicron-scale surface topography, either alone or combined with a fast-resorbing polymer binder, were mixed with autologous bone at a volume ratio of 50%:50%. Subsequently, grafts were implanted in the rabbit posterolateral spine environment with autologous bone graft as reference treatment, after which outcomes were assessed after 6, 9 and 12 weeks. PATIENT SAMPLE N/A. OUTCOME MEASURES Spinal fusion was determined by manual palpation (MP), X-ray and micro CT scan (based on the Lenke scale), mechanical testing (range of motion testing at 12 weeks only) and histology (decalcified and undecalcified). METHODS Sixty skeletally mature New Zealand white rabbits were divided into three groups and underwent single-level bilateral posterolateral intertransverse process spine arthrodesis at L4-5. Animals were euthanized 0, 6, 9 and 12 weeks for analysis of outcomes. RESULTS Based on all endpoints, the three groups showed an equivalent and gradual progression in bone formation and implant resorption during time leading to mature fusion masses at 12 weeks. No adverse reactions were observed in any of the groups. Bilateral fusion rates by MP were consistent with the literature (0%–20% at 6 weeks, 60% at 9 weeks, 75% at 12 weeks) and similar trends were seen by radiographic assessment (both X-ray and uCT). Flexion–extension and lateral bending results at 12 weeks demonstrated fusion of the treated level consistent with the MP results. By histology, from 6 weeks onwards, bone formation was observed on and between the BCP granules and within the residual autograft particles. At 9 and 12 weeks, progressive bone formation with developing marrow spaces was observed in all groups. Gradual resorption of BCP granules was evident with resorbing multinucleated or osteoclastic cells on the material surface and a decrease in material proportion over time. Histological fusion, ie, continuous bone formation between the transverse processes, for the three groups ranged 0%–20% at 6 weeks to 20%–40% at 9 weeks and 75%–87.5% at 12 weeks. CONCLUSIONS These results show that BCP with submicron-scale surface topography could achieve equivalent fusion rates to ABG when used as graft extender in a single level rabbit intertransverse process posterolateral lumbar arthrodesis model. During time, a progression in bone healing, graft resorption and remodeling was seen with all experimental endpoints, with consistency between the groups.