Introduction: Metastatic destruction of integral spinal elements increases the risk of instability, pain and neurologic deficits. The Spinal Instability Neoplastic Score (SINS) is used to assess mechanical instability based on radiographic and clinical factors. We conducted this study to evaluate the clinical utility of SINS in surgical decision-making in spinal metastasis and its association with metastatic epidural spinal cord compression (MESCC).
Methods: We allocated 285 patients with spinal metastatic disease using an oncology database, with their disease characteristics identified through a retrospective review. SINS was calculated using good-quality computed tomography (CT) imaging studies. The degree of MESCC was assessed using 0 to 3 grading system.
Results: Based on SINS, patients were categorized into stable (34.7%), potentially unstable (52.6%) and unstable (12.6%) groups. There were no cases with esophageal or small cell lung carcinomas associated with unstable SINS suggesting that some metastatic malignancies are less prone to spinal instability. Surgical interventions were employed in 20.7% of patients, and radiotherapy alone in 69.5%. In the surgical intervention group, there was 69.5% treated with decompression and instrumented fusion, 17% with decompression alone, 8.5% with percutaneous vertebral augmentation and 5% with instrumented vertebral augmentation. A significantly higher proportion of patients with stable SINS (63.6%) were treated surgically without instrumentation (X2=10.6, P=0.005), whereas instrumentation was utilized in 87.5% of patients with unstable SINS. Instability was associated with metastatic lesions at junctional spinal levels, mechanical pain, deformity, vertebral body collapse > 50% and bilateral posterolateral metastatic involvement (P<0.001). Grade 3 MESCC occurred in 65.5% of patients with unstable SINS, whereas 71.4% of patients with stable SINS had grade 0 MESCC (X2=42.1, P<0.001).
Conclusions: SINS is associated with higher degrees of MESCC and may play an important role in surgical decision-making, facilitating assessment and recognition of spinal instability in need of urgent appropriate surgical interventions.
Patient Care: This study provides clinical date highlighting the role of SINS in the surgical management of patients with spinal epidural metastases, and in improving patient selection for surgical treatment. It incorporates data concerning spinal instability and survival post-spinal metastases, and brings both factors together to describe an algorithm for better patient selection for surgical treatment. It also highlights the importance of the surveillance role of SINS in monitoring patients with spinal metastases undergoing radiation to identify patients at higher risk of developing instability.
Learning Objectives: By the conclusion of this session, participants should be able to:
1) Describe the clinical significance of SINS and its role in surgical decision making
2) Discuss, in small groups, the requirement for a more holistic surgical assessment of patients with spinal metastases incorporating prognostic as well as instability factors into the surgical decision-making process
3) Be able to use SINS and apply it in clinical practice, but also to understand its limitations
4) Describe the natural history of spinal instability in the context of spinal epidural metastases as stratified by different tumor histologies