Spinal Instability Neoplastic Score as a Predictor of Vertebral Fracture in Patients Undergoing Radiation Therapy for Spinal Metastases: A Single-Institution Study.

Purpose: The Spinal Instability Neoplastic Score (SINS) is the most common method of assessing spine stability in the setting of spinal metastases. We sought to assess (1) the SINS score as a predictor of vertebral compression fracture (VCF), (2) the risk contributions of the 6 SINS individual factors, and (3) other contributors to fracture risk.

Methods And Materials: In total, 194 patients with 391 spinal lesions that had not previously been treated with vertebroplasty/kyphoplasty, radiation therapy (RT), or surgery were enrolled before RT and followed for new or worsened fracture.

Results: A total of 187 patients who were treated to 361 vertebral levels underwent post-RT follow-up. Average follow-up time for patients on study was 9.4 months (range, 0.2-38.8 months). A total of 33 new or worsened fractures (9.1% of lesions followed) were observed, with an average time to fracture of 4.4 months (range, 0.1-27.8 months). Of all 6 SINS factors, 3 were found to be individually significantly associated with increased risk of fracture, these were: lesion location in L2-L4 [hazard ratio (HR) = 2.78, = .04], mixed or lytic appearance on computed tomography (mixed HR = 3.87, = .01, lytic HR = 2.68, = .02), and <50% vertebral collapse (HR = 3.52, < .01). SINS as a summated score was significantly associated with increased risk of fracture on multivariable analysis ( < .01). Use of bone-strengthening medications such as bisphosphonates was also significantly associated with decreased risk of fracture in multivariable analysis in stable (SINS ≤6) (HR = 0.10, = .03) and potentially unstable (SINS, 7-12) lesions (HR: 0.18, = .03).

Conclusions: These findings support that SINS is a useful tool for estimating VCF risk, with lesion location, metastasis bone morphology, and presence of <50% collapse being the strongest predictors. Additionally, findings suggest that bone-strengthening medications such as bisphosphonates may mitigate the risk of developing VCF after RT.