Patient-reported outcomes after surgical stabilization of spinal tumors: symptom-based validation of the Spinal Instability Neoplastic Score (SINS) and surgery

Background Context Neoplastic spinal instability is movement-related pain or neurologic compromise under physiologic loads with the Spinal Instability Neoplastic Score (SINS) developed to facilitate diagnosis. There is a paucity of evidence that mechanical instability correlates with patient-reported symptoms and that surgical stabilization significantly improves these patient-reported outcomes (PROs). Purpose The objective of this study was to determine if SINS correlates with patient-reported preoperative pain and disability, and if surgical stabilization significantly improves PRO. Study Design A single-institution prospective cohort study was carried out. Patient Sample A total of 131 patients who underwent stabilization for metastatic spinal tumor treatment between July 2014 and August 2016 were included. Outcomes Measures Preoperative baseline and mean difference in perioperative PROs as assessed by the Brief Pain Inventory (BPI) and MD Anderson Symptom Inventory (MDASI) were the outcome measures. Methods The SINS was analyzed as a continuous, ordinal, and categorical variable (Stable: 0–6, Indeterminate: 7–12, Unstable: 13–18). Statistical analysis was performed using Spearman rank coefficient (rho), the Kruskal-Wallis test, and an extension of the Cochran-Armitage trend test. The SINS and association between the mean differences in post- and preoperative PRO scores was analyzed using the Wilcoxon signed-rank test. Results There was a statistically significant positive correlation between increasing SINS and severity of preoperative pain with BPI average pain (rho=0.20; p=.03) and MDASI pain (rho=0.19; p=.03). Increasing SINS correlated with severity of preoperative disability with BPI walking (rho=0.19; p=.04), MDASI activity (rho=0.24; p=.006), and MDASI walking (rho=0.20; p=.03). Similar associations were noted when SINS was analyzed as an ordinal categorical variable. Stabilization significantly improved nearly all PRO measures for patients with indeterminate and unstable SINS. Significant correlations persisted when controlling for neurologic status and were not affected based on the technique of surgical stabilization used. Conclusions Patient-related outcome-based validation of SINS confirms this scoring system for diagnosing neoplastic spinal instability and provides surgeons with a tool to determine which patients will benefit from stabilization. Surgical stabilization of cancer patients with SINS consistent with mechanical instability provides significant reduction in pain and improves patient mobility independent of neurologic status and stabilization technique.