Reliability of the Spinal Instability Neoplastic Score (SINS) among radiation oncologists: an assessment of instability secondary to spinal metastases

Abstract

Background: The Spinal Instability Neoplastic Score (SINS) categorizes tumor related spinal instability. It has the potential to streamline the referral of patients with established or potential spinal instability to a spine surgeon. This study aims to define the inter- and intra-observer reliability and validity of SINS among radiation oncologists.

Methods: Thirty-three radiation oncologists, across ten international sites, rated 30 neoplastic spinal disease cases. For each case, the total SINS (0-18 points), three clinical categories (stable: 0-6 points, potentially unstable: 7-12 points, and unstable: 13-18 points), and a binary scale ('stable': 0-6 points and 'current or possible instability'; surgical consultation recommended: 7-18 points) were recorded. Evaluation was repeated 6-8 weeks later. Inter-observer agreement and intra-observer reproducibility were calculated by means of the kappa statistic and translated into levels of agreement (slight, fair, moderate, substantial, and excellent). Validity was determined by comparing the ratings against a spinal surgeon's consensus standard.

Results: Radiation oncologists demonstrated substantial (κ=0.76) inter-observer and excellent (κ=0.80) intra-observer reliability when using the SINS binary scale ('stable' versus 'current or possible instability'). Validity of the binary scale was also excellent (κ=0.85) compared with the gold standard. None of the unstable cases was rated as stable by the radiation oncologists ensuring all were appropriately recommended for surgical consultation.

Conclusions: Among radiation oncologists SINS is a highly reliable, reproducible, and valid assessment tool to address a key question in tumor related spinal disease: Is the spine 'stable' or is there 'current or possible instability' that warrants surgical assessment?

Figures

Figure 1

A 67-year-old man with known metastatic small cell lung cancer presents with interscapular back pain that is exacerbated by movement and relieved with rest. Computed Tomography (CT) (A: left parasagittal, B: midline parasagittal, C: right parasagittal, D: coronal, and E: axial) and Magnectic Resonance (MR) images (F: sagittal, T2-weighted) outline the key details of this T5 lesion. Total SINS score = Semirigid (T5) spine, 1 point; ‘Mechanical’ pain (yes), 3 points; Lytic lesion, 2 points; De novo kyphotic deformity without subluxation/translation, 2 points; >50% vertebral body collapse, 3 points; and bilateral posterolateral spinal element involvement, 3 points. Total SINS score = 1 + 3 + 2 + 2 + 3 + 3 = 14 (unstable, surgical consultation is recommended).