A finite element approach towards biomechanical optimization of prophylactic vertebroplasty
Liebschner, Michael A. K.
Doctor of Philosophy
Vertebroplasty has the potential to be a highly effective vertebral fracture prevention treatment, but the procedure must first be optimized for maximum benefit and minimal risk of safety to the patient. The procedure involves the percutaneous injection of a liquid bone cement into the vertebral body, which upon hardening provides instantaneous structural reinforcement. This research characterizes the effects of bone cement volume, material properties and distribution patterns on the global and internal vertebral biomechanics after prophylactic vertebroplasty in order to optimize these cement properties based on biomechanical efficacy and risk of complications which pose a threat to patient safety. In light of the many factors affecting the biomechanical outcome, a computational approach was employed since multiple analyses can be repeated on the same specimen. The accuracy of the models is assured by using realistic, image-based finite element models of human vertebral bodies that are specimen-specific, anatomically detailed and calibrated to experimental results. Prophylactic vertebroplasty was simulated on these models under various cement configurations and their biomechanical efficacies were evaluated based on the criteria for biomechanical success developed in this research---maximum mechanical reinforcement to reach low fracture risk levels with minimal amount of cement and maintenance of intravertebral mechanical compatibility to retain the normal dynamics of the weight-bearing spine. The biomechanically optimal bone cement is determined as one that results in a spatially dispersed distribution when injected into the vertebral body. The higher vertebral reinforcements achieved with a dispersed cement fill may lower the risk of complications due to cement leakages since smaller cement volume would be just as biomechanically effective. Furthermore, the disperse fill results in minimal intravertebral stress concentrations that may reduce the risk of subsequent fractures in the adjacent untreated vertebrae. Now that the bone cements with spatially dispersed fill patterns is known to produce optimum biomechanical effects, the biochemistry of materials with this unique characteristic can be specifically tailored to include biodegradability and drug release capabilities for various applications that require the merger of fracture prevention, tissue engineering and drug delivery innovations into one without any concerns for adverse biomechanical affects.