The biomechanics of vertebroplasty: a review

Percutaneous vertebroplasty and kyphoplasty are being used extensively in the United States for the treatment of osteoporotic vertebral compression fractures. Although shortterm clinical outcomes appear favourable, long-term data are not yet available and it is becoming increasingly important to understand how the underlying biomechanics of the spine are altered by the procedure. In vitro experimental studies have investigated the effect of cement augmentation on individual vertebra and short spinal segments. For individual vertebra, vertebroplasty appears to increase or return strength to the prefracture level, whereas the stiffness is not always restored. However for multiplevertebra segments, the strength of the unit as a whole appears to decrease, with failure occurring in the nonaugmented vertebrae. Both finite element (FE) and experimental studies have shown that the volume of cement injected affects the restoration of strength and stiffness. The type of cement appears to have less of an effect. Although biomechanical studies of the vertebroplasty process have indicated that the procedure has the potential to restore vertebral strength and stiffness, further work is necessary to understand fully the effects of the augmentation process on the surrounding structures if the treatment is to be fully optimized. This paper is a review of the biomechanical data available on vertebroplasty.