Prediction of thoracic and lumbar vertebral body compressive strength: correlations with bone mineral density and vertebral region

The bone density of thoracolumbar vertebral columns (T1 to L5) from 18 individuals was measured using quantitative computed tomography and dual energy x-ray absorptiometry. Three hundred six isolated vertebral bodies were tested in a materials test device to determine their compressive strength. Between T1 and L5 the mean segmental increase in bone mineral content was 0.3 g, while the corresponding mean decrease in trabecular density was 4.7 HU. Midvertebral body cross-sectional area increased by an average of 46 mm2 per segment and the mean segmental increase in compressive strength was 0.17 kN. Compressive strength was significantly correlated with bone mineral density measured with dual energy x-ray absorptiometry (r = 0.86). Vertebral trabecular density samples measured with quantitative computed tomography were poorly correlated with compressive strength (r = 0.28); however, this was improved when the trabecular density was multiplied by the midvertebral body cross-sectional area (r = 0.83). This study provides information concerning the relationships between density and mechanical properties of all thoracic and lumbar vertebral bodies across a wide age range. While the load-bearing capacity of the vertebral bodies is largely dependent on their geometry and bone density, this relationship has been only extensively tested for the lumbar spine. This study extends these observations over the lumbar and thoracic regions to provide a comprehensive analysis of the strength characteristics of each vertebral body. This is particularly important given the paucity of data on the thoracic spine where age-related vertebral fractures predominate. These data provide a basis for the development of models to predict the potential for thoracolumbar fractures in the elderly vertebral column.