1536 www.spinejournal.com October 2015 EPIDEMIOLOGY SPINE Volume 40, Number 19, pp 1536-1541 ©2015, Wolters Kluwer Health, Inc. All rights reserved. DOI: 10.1097/BRS.0000000000001041 Study Design. Prospective observational study. Objective. To investigate the association of perioperative vitamin D levels and nonunion rates and time to fusion in patients undergoing elective spine fusion. Summary of Background Data. Although there is a clear link between bone mineral density and the risk of osteoporosis, it is unclear whether low vitamin D levels affect rates and timing of spinal fusion. Methods. Serum 25-OH vitamin D levels were measured perioperatively in adults undergoing elective spinal fusion between 2011 and 2012. Vitamin D levels <20 ng/mL were considered deficient. Univariate and multivariate logistic regression were performed to identify independent predictors of pseudarthrosis/ nonunion within a minimum follow-up period of 12 months. Kaplan-Meier analysis was used to compare time to fusion between groups. Results. Of the 133 patients, 31 (23%) demonstrated vitamin D deficiency. Mean patient age was 57 ± 13 years; 44% were female and 94% were Caucasian. The cervical spine was fused in 49%, the lumbar spine in 47%, and the thoracic spine in 4%. Mean construct length was 2 levels (range 1–16). At 12-month follow-up, 112/133 (84%) patients demonstrated fusion (median time to fusion 8.4 mo). Nonunion at 12 months was associated with vitamin D deficiency (20% of patients with adequate vitamin D level vs. 38% of vitamin D-deficient patients, P = 0.063). Kaplan-Meier survival From the *Department of Neurosurgery, Clinical Neurosciences Center, University of Utah, Salt Lake City, UT; †Department of Neurosurgery, Barrow Neurological Institute, Phoenix, AZ; ‡University of Florida School of Medicine, Gainesville, FL; and §Department of Neurosurgery, Washington University in St. Louis, St. Louis, MO. Acknowledgment date: April 21, 2015. Acceptance date: June 23, 2015. The manuscript submitted does not contain information about medical device(s)/drug(s). No funds were received in support of this work. Relevant financial activities outside the submitted work: board membership, consultancy, grants, payment for lectures. Address correspondence and reprint requests to Wilson Z. Ray, MD, Department of Neurosurgery, Washington University in Saint Louis, 660 S. Euclid Avenue, Campus Box 8057, St. Louis, MO 63110; Email: rayz@ wudosis.wustl.edu S pinal arthrodesis has become the mainstay of treatment for severe spinal deformity, spinal instability, spondylo- listhesis, and symptomatic degenerative disease. 1 Its pri- mary goal is to develop an osseous bridge between adjacent motion segments to prevent motion, relieve pain, and facili- tate neurological recovery. Bony fusion is a dynamic process involving osteocytes, osteoclasts, and osteoblasts. 1 Level of calcium availability and vitamin D balance may affect the metabolic milieu available for development of a fusion mass. Low bone mineral density (BMD) remains the most com- mon cause of spine fractures, 2 and lower BMD secondary to osteoporosis and osteomalacia represents a known significant risk factor for both bony fracture and spinal instrumenta- tion failure. 3–7 Our group 8 and Stoker et al 9 independently demonstrated a high rate of vitamin D deficiency in patients undergoing spinal instrumentation. Although there is a clear link between BMD and the risk of osteoporosis, it is unclear whether low vitamin D levels can affect rates of fusion, time to fusion, or the incidence of instrumentation failure. The present study was designed to evaluate the relation- ship between vitamin D status and bony fusion in patients undergoing elective spinal instrumentation. A secondary goal of the study was to evaluate the association between vitamin D levels and the time to fusion. We hypothesized that patients with vitamin D deficiency would be at higher risk of nonunion analysis demonstrated time to fusion was significantly longer in the vitamin D-deficient group (12 vs. 6 mo, P = 0.001). On multivariate analysis, vitamin D deficiency was an independent predictor of nonunion (odds ratio 3.449, P = 0.045) when adjusted for age, sex, obesity , fusion length, location, graft type, smoking, and bone morphogenetic protein use. Conclusion. Vitamin D levels may affect nonunion rate and time to fusion. These results offer insight into the importance of the metabolic milieu for bony fusion as well as a potential avenue for therapeutic intervention. Key words: vitamin D deficiency, pseudarthrosis, Kaplan-Meier survival analysis. Level of Evidence: 3 Spine 2015;40:1536–1541 Vitamin D Levels and 1-Year Fusion Outcomes in Elective Spine Surgery A Prospective Observational Study Vijay M. Ravindra, MD,* Jakub Godzik, MD,† Andrew T. Dailey, MD,* Meic H. Schmidt, MD, MBA,* Erica F. Bisson, MD, MPH,* Robert S. Hood, MD ,* Andrew Cutler, BS,‡ and Wilson Z. Ray, MD§ Copyright © 2015 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited.