Biomechanics of vertebral level, geometry, and transcortical tumors in the metastatic spine

Metastatic involvement can disrupt the mechanical integrity of the spine, rendering vertebrae susceptible to burst fracture and neurologic damage. Fracture risk assessment for patients with spinal metastases is important in considering prophylactic treatment options. Stability of thoracic vertebrae affected by metastatic disease has been shown to be dependent on tumor size and bone density, but additional structural and geometric factors may also play a role in fracture risk assessment. The objective of this study was to use parametric finite element modeling to determine the effects of vertebral level, geometry, and metastatic compromise to the cortical shell on the risk of burst fracture in the thoracic spine. Analysis of vertebral level and geometry was assessed by investigation of seven scenarios ranging in geometry from T2–T4 to T10–T12. The effects of cortical shell compromised were assessed by comparison of four transcortical scenarios to a fully contained central vertebral body tumor scenario. Results demonstrated that upper thoracic vertebrae are at greater risk of burst fracture and that kyphotic motion segments are at decreased risk of burst fracture. Vertebrae with transcortical lesions are up to 30% less likely to lead to burst fracture initiation. The findings of this study are important for improving the understanding of burst fracture mechanics in metastatically involved vertebrae and guiding future modeling efforts.