Biomechanical effects of bone cement volume on the endplates of augmented vertebral body: a three-dimensional finite element analysis

Background Previous studies have suggested that percutaneous vertebroplasty might alter vertebral stress transfer, leading to adjacent vertebral failure. However, no three-dimensional finite element study so far accounted for the stress distributions on different cement volumes. The purpose of this study was to evaluate the stress distributions on the endplate under different loading conditions after augmentation with various volumes of bone cement. Methods L2-L3 motion segment data were obtained from CT scans of the lumbar spine from a cadaver of a young man who had no abnormal findings on roentgenograms. Three-dimensional model of L2-L3 was established using Mimics software, and finite element model of L2-L3 functional spinal unit (FSU) was established using Ansys10.0 software. For simulating percutaneous vertebral augmentation, polymethylmethacrylate (PMMA) was deposited into the bipedicle of the L2 vertebra. The percentage of PMMA volume varied between 15% and 30%. The stress distributions on the endplate of the augmented vertebral body were calculated under three different loading conditions. Results In general, the stress level monotonically increased with bone cement volume. Under each loading condition, the stress change on the L2 superior and inferior endplates in three kinds of finite element models shows monotonic increase. Compared with the stress-increasing region of the endplate, the central part of the L2 endplate was subject to the greatest stress under three kinds of loading conditions, especially on the superior endplate and under flexion. Conclusions The finite element models of FSU are useful to optimize the planning for vertebroplasty. The bone cement volume might have an influence on the endplate of the augmentation, especially the superior endplate. It should be noted that the optimization of bone cement volume is patient specific; the volume of the bone cement should be based on the size, body mineral density, and stiffness of the vertebrae of individual patients.