A Biomechanical Analysis of Metastatic Vertebral Collapse of the Thoracic Spine

STUDY DESIGN: This is a biomechanical study using sheep thoracic spine to investigate the probability of mechanical failure of the thoracic spine with various sizes or locations of tumor metastasis. OBJECTIVE: The objectives of this study were to investigate biomechanical effects of not only tumor sizes within the thoracic vertebral body but also its involvement of other spinal components on the probability of mechanical failures of the thoracic spine. SUMMARY OF BACKGROUND DATA: There have been no experimental studies concerning mechanical influences of destruction of costovertebral joint or posterior elements as well as vertebral body on the load-bearing capacity of the thoracic spine. METHODS: Ninety-nine fresh sheep thoracic spine specimens with ribs were used (T7-T9, T10-T12). Within vertebral bodies of 39 specimens, only trabecular defects were created in different sizes. In other 48 specimens, not only vertebral body defects that were 40% to the cross-sectional area of the vertebral body but also additional destruction of costovertebral joint, pedicle, and facet joint were created. All specimens were subjected to destructive biomechanical testing. RESULTS: The failure load decreased as the defect size in the vertebral body increased. A negative linear correlation was observed between the failure load and the size of vertebral body defect (r = 0.782). With 40% cross-sectional defect in the vertebral body, additional costovertebral joint destruction brought 25% reduction of the failure load, which was statistically significant. CONCLUSION: The load-bearing capacity of metastasized vertebrae in the thoracic spine was proportionally decreased when the defect size in the vertebral body increased. Destruction of costovertebral joint significantly increased the probability of vertebral collapse.