The relationship between serum vitamin D levels and spinal fusion success: a quantitative analysis.

Abstract

An in vivo dosing study of vitamin D in a rat posterolateral spinal fusion model with autogenous bone grafting. Rats randomized to 4 levels of vitamin D-adjusted rat chow, longitudinal serum validation, surgeons/observers blinded to dietary conditions, and rats followed prospectively for fusion endpoint. To assess the impact of dietary and serum levels of vitamin D on fusion success, consolidation of fusion mass, and biomechanical stiffness after posterolateral spinal fusion procedure. Metabolic risk factors, including vitamin D insufficiency, are often overlooked by spine surgeons. Currently, there are no published data on the causal effect of insufficient or deficient vitamin D levels on the success of establishing solid bony union after a spinal fusion procedure. Fifty rats were randomized to 4 experimentally controlled rat chow diets: normal control, vitamin D-deficient, vitamin D-insufficient, and a nontoxic high dose of vitamin D, 4 weeks prior to surgery and maintained postsurgery until sacrifice. Serum levels of 25(OH)D were determined at surgery and sacrifice using radioimmunoassay. Posterolateral fusion surgery with tail autograft was performed. Rats were sacrificed 12 weeks postoperatively, and fusion was evaluated via manual palpation, high-resolution radiographs, micro-computed tomographic scans, and biomechanical testing. Serum 25(OH)D and calcium levels were significantly correlated with vitamin D-adjusted chow (P < 0.001). There was a dose-dependent relationship between vitamin D-adjusted chow and manual palpation fusion, with greatest differences found in measures of radiographical density between high and deficient vitamin D (P < 0.05). Adequate levels of vitamin D (high and normal control) yielded stiffer fusion than inadequate levels (insufficient and deficient) (P < 0.05). Manual palpation fusion rates increased with supplementation of dietary vitamin D. Biomechanical stiffness, bone volume, and density were also positively related to vitamin D and calcium. N/A.