Biomechanical assessment of stability in the metastatic spine following percutaneous vertebroplasty: effects of cement distribution patterns and volume.

Percutaneous vertebroplasty is a minimally invasive, radiologically guided procedure whereby bone cement is injected into structurally weakened vertebrae to provide added biomechanical stability. In addition to treating osteoporotic vertebral fractures, this technique is also used to relieve pain by stabilizing metastatically compromised vertebrae that are at risk of pathologic burst fracture. Optimal cement distribution patterns to improve biomechanical stability to metastatically involved vertebral bodies remain unknown. This study aimed to determine the effect of cement location and volume of cement injected during percutaneous vertebroplasty on improving vertebral stability in a metastatically-compromised spinal motion segment using a parametric poroelastic finite element model. A three-dimensional parametric finite element model of a thoracic spinal motion segment was developed and analyzed using commercially available software. A total of 16 metastatic pre and post vertebroplasty scenarios were investigated using a serrated spherical representation of tumor tissue and various geometric representations of polymethylmethacrylate (PMMA). The effect of vertebroplasty on vertebral bulge, a measure of posterior vertebral body wall motion as an indicator of burst fracture initiation, was assessed. In all cases, vertebroplasty reduced vertebral bulge, but the risk of the initiation of burst fracture was minimized with cement located posterior to the tumor, near the posterior vertebral body wall. Vertebral bulge decreased by up to 62% with 20% cement injection. These findings demonstrate that location and distribution of cement within the vertebral body has a noticeable effect on the restoration of biomechanical stability following percutaneous vertebroplasty.