In vivo evaluation of porous Hydroxylapatite ceramic as cervical vertebra substitute

Introduction: Hydroxylapatite ceramic has been used as a bone substitute for grafting in extensive bone replacement. This study determined the efficacy of solid porous Hydroxylapatite (PHA) blocks as substitute for partial cervical vertebrae in a canine model. Methods: The PHA blocks were implanted as graft into the defect of C3-C4 vertebrae in 8 adult dogs. The required segments were dissected 6 months postoperation. Radiographic evaluation including plain radiographs and computed tomography (CT) were used to determine fusion quality. The specimens were also subjected to mechanical testing including compressive testing and flexion/extension testing. The sections were stained with HE and Van Gieson and were analyzed. SEM and EDAX were performed on other specimens. Result: The radiographic images demonstrated progressive incorporation of the PHA blocks with time. There were statistical differences in compressive strength, Youngʹs modulus and bending stiffness between implanted PHA blocks and pure PHA blocks (P < 0.05). The implanted blocks were more durable and stiffer. The histologic findings demonstrated the formation of new bone directly in pores of the PHA blocks and adjacent to the surface of the blocks. The new bone has a normal texture and has directly grown into the PHA blocks without interposition of connective tissue. Conclusion: This study determined the biocompatibility, osteogenic potential and acceptable biomechanical properties of PHA blocks as graft of partial cervical vertebrae. The results indicated that PHA blocks may be a promising alternative to autogenous graft materials as a substitute for partial cervical vertebrae.