Effects of tumor location, shape and surface serration on burst fracture risk in the metastatic spine

Spinal metastatic disease occurs in up to one-third of all cancer patients. Advanced spread can lead to vertebral burst fracture, which may result in neurologic compromise. Developing a better understanding of factors affecting burst fracture risk has significant clinical importance, as early intervention can prevent vertebral fracture in high-risk patients. The primary objective of this study was to quantify the effects of tumor location and shape on vertebral body stability and burst fracture risk in the metastatic spine using poroelastic parametric finite element modeling. This study also compared two distinct surface modeling techniques in the representation of lytic defects. A total of 16 ellipsoidal tumor scenarios were analyzed. Single tumors were situated in central, anterior, posterior, superior, inferior, and lateral locations, with smooth and serrated tumor surfaces. Two central shapes and two serrated surface multi-tumor scenarios were also analyzed. Outcome parameters of maximum vertebral bulge and axial displacement were assessed as representative of burst fracture risk. Posterior movement of the tumor caused the greatest increase in vertebral bulge. Tumor shape also affected burst fracture risk. The multi-tumor scenarios yielded the greatest reductions in both vertebral bulge and axial displacement. Serrated tumor scenarios abided by similar trends as smooth tumor scenarios, although tumor serration caused a slight increase in fracture risk. Tumor shape and volume are best controlled by smooth surface modeling. Improved understanding of factors contributing to metastatic burst fracture risk will aid in directing future modeling efforts and in the development of accurate risk assessment criteria.