Load sharing within a human lumbar vertebral body using the finite element method.

STUDY
DESIGN: A finite element parametric study was performed to investigate the structural roles of the vertebral cortical shell and the trabecular centrum.
OBJECTIVES: To address the debated issue of the relative load-carrying role of the vertebral cortical shell. SUMMARY OF BACKGROUND DATA: Several experimental and computational studies have been aimed at quantifying the load-carrying roles of the human vertebral cortical shell and trabecular centrum. These studies, however, have supported no consensus.
METHODS: A finite element model of three lumbar vertebral bodies was developed to predict the fraction of the total compressive load acting on the lumbar vertebral body, under two different loading conditions, that was supported by the cortical shell. Parametric variations in vertebral material and geometric properties were examined to determine how this fraction was influenced by such changes.
RESULTS: The fraction of the compressive load supported by the cortical shell was found to be strongly dependent on the distance from the endplate, increasing from about 34% at either endplate to approximately 63% at the midtransverse plane. This fraction was independent of the loading characteristics, proportional to the properties of the cortex, and inversely proportional to the modulus of the centrum. Additionally, the cortical shell force fraction was affected significantly by changes in the overall vertebral geometry.
CONCLUSIONS: Our findings indicate that the structural dominance of the cortical shell and centrum alternate depending on the location within the vertebral body. However, as age-related bone loss progresses, the load-carrying role of the cortical shell could increase significantly.