Strength reductions of thoracic vertebrae in the presence of transcortical osseous defects: effects of defect location, pedicle disruption, and defect size

Transcortical osseous lesions were simulated in thoracic vertebrae to investigate the effects on vertebral strength of defect location, pedicle disruption, and defect size. Alternate vertebrae from 15 thoracic spines were assigned to five defect groups: anterior, posterior, lateral, one pedicle, or both pedicles. The remaining vertebrae served as controls. All vertebrae were tested to failure in combined axial - flexion loading. The intact failure load for each vertebra with a defect was estimated based on the actual failure loads of the control vertebrae from the same spine. The failure loads for vertebrae with transcortical defects (anterior, posterior, lateral) were significantly lower (P=0.0001) than estimated intact loads; this was not the case for vertebrae with single pedicle disruption (P=0.90). Relative strengths (defined as actual failure load divided by predicted intact failure load) for the anterior (mean=0.51), posterior (0.55) and lateral (0.58) defect groups were not significantly different from each other, but were different from the single pedicle defect group (1.09). Relative strength depended only weakly on defect size. Comparison of these results with those of a previous study of simulated defects in the vertebral centrum suggests that transcortical defects result in slightly greater reductions in vertebral strength than defects of comparable size involving only trabecular bone.