Assessment of Bone Bridging of a Novel Wet-Field Regenerative Bone Adhesive for Lumbar Spine Fusion in an Ovine Model at 12, 26, and 52 Weeks.

BACKGROUND: Current techniques for instrumented posterolateral lumbar fusion include the use of titanium rods and pedicle screws to provide mechanical fixation, while autograft and/or allograft bone is used to promote osseous union across the fusion site. Although bone graft substitutes may be used for this purpose, they can resorb before a solid fusion is established, leading to nonunion. Tetracalcium phosphate-phosphoserine (TTCP-PS) is a novel, bioresorbable, osteoconductive, wet-field mineral-organic bone adhesive and bone graft substitute that has been previously shown to promote bone healing in a number of applications, including cranial bone flap fixation.

OBJECTIVE: The goal of this study was to investigate the use of TTCP-PS for fusion in a posterolateral lumbar ovine model and to compare it to a commercially available bone graft substitute.

STUDY DESIGN: An ovine lumbar fusion model was used to evaluate the safety and efficacy of TTCP-PS mineral-organic bone adhesive compared with a currently marketed bone graft substitute as a control (Actifuse ABX) over 1 year. These substances were implanted bilaterally in 20 sheep between the L3-L4 and L4-L5 transverse processes, stabilized with a pedicle screw fixation system.

METHODS: Postoperative x-ray images, computed tomography scans, and histological findings were assessed at 12, 26, and 52 weeks after implantation to evaluate lumbar fusion across groups and time points.

RESULTS: After euthanasia at 12 weeks, no statistically significant differences in the bone deposition region of interest at any of the substance implantation sites were observed. At 26 weeks, histologic analysis demonstrated new bone formation percentage to be significantly greater (P = 0.001) in the TTCP-PS sites (57%) than in the control group sites (31%). By 52 weeks, no statistically significant difference was found between groups, although the mean percentage bone growth area remained higher for the bone adhesive (52%) compared with the control (45%).

CONCLUSIONS: TTCP-PS was safe and effective in an ovine posterolateral lumbar fusion model. TTCP-PS promoted earlier and greater (26 weeks) bone bridging in this study than a currently marketed bone graft substitute (Actifuse ABX) while producing greater levels of bone formation at 1 year after surgery. This accelerated healing may aid implant stabilization and reduce the risk of nonunion in posterolateral lumbar fusions in humans.

CLINICAL RELEVANCE: TTCP-PS was demonstrated to be safe and effective as a bone graft substitute in this large animal posterolateral spinal fusion model. Its use resulted in superior new bone volume, greater mineral density of the fusion mass, and more rapid bone ingrowth than the control. These properties of TTCP-PS bone adhesive may improve the reliability and success of spinal fusion procedures.