Seasonal Variation of Vitamin D, PTH, and Bone Turnover Markers in Patients Undergoing Lumbar Fusion Surgery

STUDY DESIGN: Secondary analysis of a prospective cross-sectional study at an academic tertiary spine care center. OBJECTIVES: To examine the prevalence and risk factors for preoperative Vitamin D (VitD) deficiency and secondary hyperparathyroidism (SHPT), and to assess the seasonal variation of metabolic bone laboratory parameters in patients undergoing lumbar fusion surgery (LFS). SUMMARY OF BACKGROUND DATA: LFS relies on adequate connective tissue quality and bone healing capacity. VitD deficiency and SHPT significantly impact bone metabolism and are linked to lower fusion rates and poorer bone quality. However, their seasonal variation in LFS patients remains unexplored. METHODS: Patients undergoing LFS for degenerative conditions received preoperative VitD, parathyroid hormone (PTH), and bone turnover markers laboratory routinely from December 2014 to December 2023. Descriptive and comparative statistics, logistic regression, and univariable and multivariable cosinor regression models were used to evaluate VitD status, SHPT prevalence, their risk-factors and seasonal variations in VitD, PTH, and bone turnover markers. RESULTS: Data from 431 patients (49% female, median age 64 y) was analyzed. VitD insufficiency (