Locally Delivered Ascorbic Acid and β-Glycerophosphate Augment Local Bone Graft in a Murine Model of 2-Level Posterior Spinal Fusion.

Abstract

Ascorbic acid is involved in collagen biosynthesis and upregulates alkaline phosphatase, potentially alleviating cell senescence and stimulating mesenchymal stem cell proliferation and differentiation into osteoblasts. We hypothesized locally delivered ascorbic acid and β-glycerophosphate act as a bone graft extender to increase the volume of new bone formed in a murine model of posterior lumbar fusion. Collagen sponges were used as delivery vehicles. Sponges were prepared with primary media alone or with the addition of ascorbic acid and β-glycerophosphate. Fresh morselized bone graft from 12 donor mice was used. Twenty-four healthy male C57BL/6 mice underwent an uninstrumented posterior L3-L5 lumbar fusion. One control group received morselized bone only. A second "sponge control" group received morselized bone with the control collagen sponge. The third group received morselized bone and a collagen sponge with ascorbic acid and β-glycerophosphate. Three months postoperatively, the lumbar spine underwent high-resolution micro-computed tomography for analysis of bone formation, density, and bridging fusion. Animals receiving ascorbic acid and β-glycerophosphate had a statistically significant increase in corrected bone volume compared with control and sponge groups, with a 56.3% and 25.4% increase, respectively. Mineralized bone fraction was statistically significantly decreased for animals in the ascorbic acid group compared with control and sponge groups. There was no significant difference in fusion rate between test groups. Locally delivered ascorbic acid and β-glycerophosphate in a murine model of posterior spinal fusion yielded statistically significant increases in new bone formation in the lumbar spine but statistically significant decreases in mineralized bone fraction. Differences in fusion rate were not statistically significant. This study provides early data suggesting that delivery of ascorbic acid to a spinal fusion site may be beneficial but does not yet establish an indication for clinical use. Further studies are needed to determine optimal dose and delivery of ascorbic acid.