Mechanical analysis of percutaneous sacroplasty using CT image based finite element models.

Sacral insufficiency fractures are an under-diagnosed source of acute lower back pain. A polymethylmethacrylate (PMMA) cement injection procedure called sacroplasty has recently been utilized as a treatment for sacral insufficiency fractures. It is believed that injection of cement reduces fracture micromotion, thus relieving pain. In this study, finite element models were used to examine the mechanical effects of sacroplasty. Finite element models were constructed from CT images of two cadavers on which sacroplasties were performed. The images were used to create the mesh geometry, and to apply non-homogeneous material properties to the models. Models were created representing the case with and without cement, thus simulating the pre- and post-sacroplasty situation. The results indicate that the sacrum has a 3D multi-axial state of strain. While compressive strains were the largest, tensile and shear strains were significant as well. Cement in the sacrum reduced strains 40-60% locally around the cement. However, overall model stiffness only increased 1-4%. This indicates that the effects of sacroplasty are primarily local.