Predicting mechanical failure in spinal metastases: from clinical scores to patient-specific biomechanical modeling

Spinal metastases are a major cause of pain, vertebral fracture, instability, and neurological compromise. The Spinal Instability Neoplastic Score (SINS) has substantially improved the standardized assessment of neoplastic spinal instability and remains the reference clinical tool for evaluating the mechanical component of metastatic spinal disease. However, it remains a semi-quantitative score, does not directly quantify vertebral strength, and is particularly limited in the intermediate SINS range (7-12), where uncertainty regarding true mechanical risk and therapeutic strategy is often greatest. In this context, vertebral mechanical failure is better understood as the consequence of an imbalance between applied spinal load and residual vertebral strength rather than as a purely morphological imaging abnormality. This review examines the current clinical approach to vertebral mechanical failure in spinal metastases and discusses the potential contribution of patient-specific biomechanical modeling, especially CT-based finite element modeling, to a more quantitative and individualized assessment of mechanical failure risk. Finite element models offer a mechanistically grounded framework that integrates vertebral geometry, lesion characteristics, bone density, and loading conditions to estimate vertebral strength more directly than current clinical scores. Experimental and ex vivo studies support their biomechanical relevance, while recent translational developments suggest increasing feasibility for clinical implementation. Rather than replacing existing clinical frameworks, finite element modeling may become a valuable extension of current assessment, particularly in patients with intermediate-risk lesions in whom decision-making remains uncertain.