gms | German Medical Science

Objectives: Spinal fusion surgery relies on good bone metabolism to prevent complications, such as non-union or proximal junctional kyphosis. To enhance preoperative optimization, this study aims to evaluate the prevalence and seasonal variation of Vitamin D (VitD) deficiency and secondary hyperparathyroidism, as well as the bone resorption parameter bone-specific alkaline phosphatase (BAP), in patients undergoing lumbar fusion surgery (LFS).

Methods: This cross-sectional study was conducted at an academic tertiary center and included patients who underwent LFS for degenerative conditions between 2016 and 2023. Patients without preoperative VitD laboratory were excluded. Preoperative serum levels of 25-OH-Cholecalciferol (VitD), parathyroid hormone (PTH), and BAP were measured. Prevalence of VitD insufficiency (<30 ng/mL), deficiency (< 20 ng/mL), and secondary hyperparathyroidism (PTH>65 pg/mL with normal calcium levels) were calculated and descriptive and comparative statistics alongside univariable logistic regression analysis, Seasonal variations were analyzed using univariable and multivariable cosinor regression analysis, which incorporated the Midline Estimating Statistic of Rhythm (MESOR), the month of the peak, and the seasonal relative peak (SRP = Amplitude/MESOR) parameter, with adjustments for confounders.

Results and conclusion: Of the 500 patients screened, 429 (86%) had preoperative VitD laboratory values. Among them, 51% were female, the median age was 65 years (IQR 56–72), and the average BMI was 29.6 (SD ±6.1). The prevalence of insufficient VitD status was 34%, including 8% with VitD deficiency. 25% of the patients had (mild) secondary hyperparathyroidism. A significant association was found between VitD status and seasonality (p < 0.001). The highest prevalence of insufficient VitD status (48%, including 13% deficiency) and secondary hyperparathyroidism (30%) was observed during the winter months (December–February), while the lowest prevalence was found in summer (June–August) with VitD insufficiency at 24% (including 6% deficiency) and (mild) secondary hyperparathyroidism at 17%. Younger age was identified as a significant risk factor for VitD deficiency (OR 0.97, 95% CI 0.94–0.99, p=0.01). Univariable cosinor regression analysis revealed VitD MESOR serum level was 39.8 mg/dL (SE 0.9, p<0.0001) with a SRP of 8% above the MESOR (SE 3%, p<0.014) in late July.For PTH, the MESOR serum level was 52.6 pg/mL (SE 1.6, p<0.0001) with a SRP of 14% above the MESOR (SE 4%, p=0.001) in February. The MESOR for BAP was 14.8 µg/L with a SRP of 14% above the MESOR (SE 4%, p<0.0001) in November/December. After adjusting for age, all parameters showed higher seasonal variances.

This study found a notable proportion of VitD deficiency and hyper-PTH with subsequent variation of BAP in patients undergoing spinal fusion surgery. These results, combined with the SV of VitD, PTH and BAP demonstrate the need for higher diagnostic awareness.