Biomechanical Characterization of healthy and metastatic vertebrae using Digital Image Correlation

Bone metastases mainly affect the spine, leading to pain and increased risk of fracture. Assessing mechanical response and fracture mechanism in metastatic vertebrae is still a biomechanical and clinical challenge. The aim of this work was to identify the most strained region in metastatic vertebrae and evaluate the effects of the metastatic feature on the mechanical properties of the vertebrae. In this study, ten spinal segments consisting of metastatic vertebrae and adjacent healthy controls were prepared from five human spines. The specimens were biomechanically tested under three different loading conditions (axial compression, flexion and torsion). Digital Image Correlation (DIC) was employed to assess the full-field strain distribution over the entire vertebral bodies. The outcomes of the study showed that no differences exist in the mean principal strains between the metastatic and control vertebrae in axial compression. However, some local differences in strain patterns and principal strain directions dependent on metastatic type and location were identified in the specimen with mainly less degenerated intervertebral discs. In contrast, during flexion, lytic vertebrae exhibited a different mean minimum strain to control ones, while under torsional loading, differences between blastic and control vertebrae principal strains became evident. During flexion and torsion, consistent principal strain patterns and directions irregularities were observed both in control and metastatic vertebrae. These findings highlight the importance of considering both metastatic features and intervertebral disc degeneration when developing clinical tools to assess vertebral mechanical competence and fracture risk. Moreover, the analysis of principal strain directions should be further explored in future studies, resulting in a promising approach to gain deeper insights into the metastatic vertebrae biomechanics.