Bone Turnover Markers as a New Predicting Factor for Nonunion After Spinal Fusion Surgery

Study Design. Retrospective observational study. Objective. We investigated whether bone turnover markers could be a useful indicator for prediction of nonunion. Summary of Background Data. Nonunion is a major complication of lumbar spinal fusion surgery. The involvement of bone turnover in the process of bony union in spinal fusion surgery is, however, poorly understood. Methods. Of the 74 patients analyzed, 13 were diagnosed with nonunion. We evaluated the significance of the following risk factors: age, sex, number of fused segments, serum levels of total alkaline phosphatase, procollagen type 1 amino-terminal propeptide (P1NP), tartrate-resistant acid phosphatase 5b (TRACP-5b), and albumin, and history of diabetes mellitus, cigarette smoking, or alcohol use. We also defined the bone turnover ratio (BTR) as a value that equals serum TRACP-5b concentration divided by serum P1NP concentration to evaluate patients' individual bone turnover balance and investigated the significance of BTR as a risk factor. Results. Univariate analysis showed that older age, malnutrition, and lower P1NP are risk factors for nonunion. Stepwise logistic regression analysis revealed that in the presence of lower P1NP, higher TRACP-5b becomes a risk factor. Furthermore, we identified BTR as the most significant risk factor for nonunion. The optimum cut-off value of BTR by receiver-operating characteristic curve was 11.74. Conclusion. These findings show a relation between bone turnover and nonunion after spinal fusion surgery. The measurement of bone turnover markers could potentially be used to predict nonunion after spinal fusion surgery. Level of Evidence: 4