Reliability of the Spinal Instability Neoplastic Scale Among Radiologists: An Assessment of Instability Secondary to Spinal Metastases

OBJECTIVE. The spinal instability neoplastic scale (SINS) is a new classification system for tumor-related spinal instability. The SINS may prove to be a valuable tool for radiologists to communicate with oncologists and surgeons in a standardized evidence-based manner. The objective of this study was to determine the inter-and intraobserver reliability and validity of the SINS among radiologists. MATERIALS AND METHODS. Thirty-seven radiologists from 10 international sites used the SINS to categorize the degree of spinal instability in 30 patients with spinal tumors. To assess validity, we compared the SINS scores assigned by the radiologists with the SINS scores of 11 spine oncology surgeons (reference standard). Each total SINS score (range, 0-18 points) was converted into one of the following three clinical categories: 0-6 points, stable; 7-12 points, potentially unstable; and 13-18 points, unstable. In addition, each total SINS score was converted into a binary scale: 0-6 points was defined as stable, and 7-18 points was considered a current or possible instability for which surgical consultation is recommended. RESULTS. Radiologists using the SINS binary scale showed excellent (kappa = 0.88) validity, substantial (kappa = 0.76) interobserver agreement, and excellent (kappa = 0.82) intraobserver reproducibility. Radiologists rated all unstable cases and 621 of 629 (98.7%) potentially unstable cases with a SINS score of 7 or more points, thus appropriately initiating a referral for surgical assessment. CONCLUSION. SINS is a reliable tool for radiologists rating tumor-related spinal instability. It accurately discriminates between stable and potentially unstable or unstable lesions and, therefore, can guide the need for surgical consultation.