Can the spinal instability neoplastic score prior to spinal radiosurgery predict compression fractures following stereotactic spinal radiosurgery for metastatic spinal tumor? a post hoc analysis of prospective phase II single-institution trials

The aim of this study was to determine the predictability of vertebral compression fracture (VCF) development applying the spinal instability neoplastic score (SINS) prior to delivery of stereotactic spinal radiosurgery (SSRS) for spinal metastases. From two prospective cohorts of SSRS for spinal metastases, we selected patients with a low degree of cord compression or cauda equine from C3 to S1 and analyzed 79 patients enrolled according to binary SINS criteria. The primary endpoint was the development of a de novo VCF or progression of an existing fracture after SSRS. We identified 32 fractures (40.5 %): 19 de novo and 13 progressive. The mean time to fracture after SSRT was 3.3 months (range, 0.4–34.1 months). In 41 patients with low SINS (0–6), 7 patients (17.1 %) developed a fracture after SSRS. In 38 patients with high SINS (7–12), 25 (65.8 %) developed a fracture. Among the 32 fractures, 15 were symptomatic. Patients with high SINS were more likely to experience symptomatic fractures (31.6 %) than were patients with lower SINS (7.4 %). On univariate and multivariate analysis, 24-month fracture-free rates were 78.7 and 33.7 % in low and high SINS group, respectively and high SINS was found to be a significant risk factor for VCFs and symptomatic fractures (respectively, HR 5.6, p = 0.04; HR 5.3, p = 0.01). SINS is a useful tool for predicting the development of VCF after SSRS for spinal metastases. Prophylactic cement augmentation should not be considered for patients with lower SINS, since the risk of fracture is low.