• J R Dimar, M J Voor, Y M Zhang, and S D Glassman.
• Department of Orthopaedic Surgery, University of Louisville School of Medicine, Kentucky, USA.
• Spine. 1998 Jun 1; 23 (11): 1209-14.

Study DesignThoracic vertebrae were subjected to compressive loads after drilling of the centrum to simulate destruction from metastatic tumorous involvement.ObjectiveTo determine whether a threshold exists that is predictive of fractures to establish a correlation between significant variables and vertebral strength.Summary Of Background DataThe mechanical effects of metastatic destruction of thoracic vertebral bodies and their correlation to pathologic fractures has been analyzed in few studies. In additional studies on intact vertebral strength, investigators have determined that bone mineral density and geometric factors are important.MethodFifty-four cadaveric thoracic vertebrae were studied. All were examined by quantitative computed tomography. T4 and T10 served as mechanical controls to predict the intact strength of T7. The test vertebrae were drilled from the anterior cortex through to the posterior cortex before they were loaded.ResultsLinear correlation between the strength of T4 and T10 in each spine supported the predicted strengths of T7. Because of variation from other factors, no threshold defect size was noted beyond which failure consistently occurred. Results of linear correlation analyses showed that the best combination of parameters for predicting vertebral strength was the product of bone mineral density and the remaining intact vertebral body cross-sectional area. This vertebral strength index correlated linearly with the strength of intact and compromised T7 vertebrae (r2 = 0.52).ConclusionsThe vertebral strength index can be used to predict the strength of any thoracic vertebra. When compared with an idealized vertebral strength index based on the intact vertebral cross-sectional area and normal bone mineral density, a patient's actual vertebral strength index can be used as one of the criteria for prophylactic stabilization.

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