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Chemical composition of ceramics affects the longevity of CRM in posterolateral lumbar fusion achieved by rhBMP6 in autologous blood coagulum with ceramic particles in rabbits

Background/Introduction: Autologous bone graft substitute (ABGS) containing rhBMP6 in autologous blood coagulum (ABC) as a BMP carrier combined with compression resistant matrix (CRM) is a novel therapeutic solution for bone regeneration. Purpose: The aim of this study was to evaluate synthetic ceramics with different particle size and chemical composition of particles as a CRM in posterolateral lumbar fusion (PLF) rabbit model. Methods: ABGS implants were prepared as follow: rhBMP6 (125 mg) was added to autologous blood (2, 5 mL) which was mixed with synthetic ceramic particles and left to coagulate. Tested ceramic particles differed in particle size (74-420 μm and 500-1700 μm) and chemical composition (TCP and biphasic ceramics containing TCP and HA in 40/60 ratio). ABGS implants (n=6 per group) were implanted bilaterally between lumbar transverse processes (L5-L6) of New Zealand White Rabbits. At the end of the follow up period (27 weeks) animals were killed and spine specimens were analysed by microCT, histology and biomechanical testing. Results: Successful spinal fusion was observed in all animals regardless of the size and chemical composition of tested ceramic particles. However, microCT analyses revealed that chemical composition of ceramics determined longevity of CRM. Specifically, TCP ceramics regardless of the particle size were significantly resorbed while particles containing large proportion of HA were only partially resorbed. Osseointegration of newly formed bone with adjacent transverse processes was observed in all specimens. Moreover, biomechanical testing revealed that adjacent transverse processes were rebridged with biomechanically competent bone. Conclusion(s): A novel ABGS containing rhBMP6 within ABC successfully promoted lumbar fusion with different ceramic particles used as a CRM. However, the chemical composition of ceramics significantly affected CRM resorbability.

ABGS ; ABC ; posterior lumbar fusion ; rhBMP6 ; ceramic ; rabbit

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