FUNCTIONAL BIOMECHANICS OF THE THORACOLUMBAR VERTEBRAL CORTEX

Studies were conducted on human cadaver thoracolumbar vertebrae, at the T//1//2-L//5 level, of five males and six females. Isolated vertebral bodies, free of posterior elements, were first scanned using dual photon absorptiometry and then underwent axial compressive loading. All of the vertebral bodies failed as a result of compressive fractures of the bone. Results indicated that the mechanical load-deflection response was nonlinear and biphasic. The mean cross-sectional areas of the vertebral bodies progressively increased from L//1 to L//5. The maximum load carrying capacity was not dependent upon spinal level. The bone mineral content (BMC) obtained using dual photon absorptiometry in the lateral projected plane increased from L//1 to L//5. Male vertebral bodies consistently had higher BMC than female specimens. The cortical shell contributed 12. 44% (mean) of the total cross-sectional area in the male, 17. 56% in the female; 8. 85% of the BMC in the male and 16. 54% in the female. In contrast, it accounted for 43. 8% (mean of the total load in the male compared to 35. 2% in the female specimens.