CLINICALLY RELEVANT PARAMETERS TO STRATIFY THE RISK OF FRACTURE IN VERTEBRAE WITH METASTASES: INSIGHT FROM BIOMECHANICAL EXPERIMENTS

Stratification of the risk of fracture in patients with vertebral metastases is one of the healthcare systems challenges. The spine, in fact, is the anatomical site where bone metastases most frequently spread. These lesions may lead to vertebral fractures, which dramatically reduce the quality of life of oncology patients and increase the costs associated to their treatment. The current clinical stratification tools lack of reliability. Moreover, discording results are reported concerning the effects of the metastatic lesions properties on the vertebral mechanical strength. There is the need of experimental measurements that show the mechanical behaviour of metastatic vertebrae. These measurements could improve our understanding of the problem and provide evidence for the validation of (data-driven/mechanistic) computational models for the stratification of metastatic patients. 50 specimens consisting of a metastatic and an adjacent control (radiologically healthy) vertebra were extracted from 30 spines from donors with spinal metastases. State of the art imaging (CT, MRI, micro-CT), multiaxial mechanical testing, and full-field strain measurements (Digital Image Correlation and Digital Volume Correlation) were combined to evaluate microstructural and mechanical properties of the vertebrae and intervertebral discs (IVD). The specimens were initially tested in the elastic regime under different loading conditions (compression, flexion, torsion) to study the physiological behaviour, and in compression up to failure in order to evaluate the failure pattern. Bone metastases were found to affect only locally the vertebral microstructure, leaving unaltered the tissue surrounding the bone. The size and location of lytic metastases explained more than 70% of the mechanical properties (i.e. deformation) of the metastatic vertebrae. Conversely, no correlation was found between these two variables for vertebrae with blastic metastases, which showed high level of mineralisation but low stiffness. The analysis of the local deformation (Fig.1) revealed the highly heterogeneous deformation distribution within the metastatic vertebrae, suggesting a sub-optimal bone microstructure. Finally, IVD degeneration affected the mechanical behaviour of the metastatic vertebrae, inducing different deformation pattern and, consequently, different failure mode. In conclusion, these studies are providing comprehensive knowledge about the mechanical behaviour of metastatic vertebrae, identifying those clinical parameters (ie. lesion size/location, IVD degeneration) that can be used to better stratify patients with metastatic vertebrae. Acknowledgements: METASTRA project funded by the European Union, HEU topic HLTH-2022-12-01, grant 101080135.