SINS Score and Stability: Evaluating the Need for Stabilization Within the Uncertain Category

Objective: The Spinal Instability Neoplastic Score (SINS) is widely used to assess mechanical instability in metastatic spine disease. We sought to identify a cutoff within the “potentially unstable” category, above which lesions were more likely than not to be stabilized. Methods: We retrospectively reviewed all patients consulted for metastatic spine disease over a 1-year period. Patients were included if they were neurologically intact and had complete medical records, including preoperative imaging of every tumor-involved level. Examined variables included epidural spinal cord compression, SINS, revised Tokuhashi grade, age at consultation, and Karnofsky Performance Status. The primary endpoint was whether or not the lesions were stabilized. Results: The study cohort comprised 51 patients (average age, 61 ± 2 years) with a total of 436 lesions; 50.5% were lytic, and 31.4% were blastic. The most common primaries were lung (n = 12), breast (n = 10) and prostate (n = 8). The median SINS across all lesions was 5. In both lesion- and patient-based analysis, a SINS ≥10 portended a >50% probability of undergoing stabilization; only 11% of all patients with a SINS ≤9 underwent instrumented fusion. Multivariable analysis demonstrated that SINS (odds ratio [OR], 2.44; P < 0.01) and Karnofsky Performance Status (OR, 1.10; P < 0.01) were independent predictors of stabilization. Conclusions: For vertebrae affected by metastatic disease, the decision to stabilize remains dependent on both the radiographic lesion properties and the patient's clinical picture. However, our results suggest that lesions with a SINS of ≤9 might not require stabilization.