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.