Effect of bone density on vertebral strength and stiffness after percutaneous vertebroplasty

Study Design. An ex vivo biomechanical study using cadaveric vertebral bodies. Objective. To determine how bone mineral density (BMD) affects mechanical strength and stiffness of the vertebral body after vertebroplasty, and to determine how the association between mechanical properties and BMD varies with amount of cement injected. Summary of Background Data. Adverse events associated with vertebroplasty include cement leakage and adjacent fractures. Understanding effects of bone density and cement volume on mechanical properties may be important clinically to identify the minimum cement volume that will benefit the patient while minimizing risks of adverse events. Methods. The bone mineral density of 13 vertebral columns from adult white female cadavers was measured with DEXA. Vertebral bodies (n = 126) were assigned to 5 groups based on cement treatment: intact, untreated, 4% fill, 12% fill, and 24% fill. Treated specimens were first loaded asymmetrically to simulate a wedge compression fracture before injection with polymethylmethacrylate cement. Strength and stiffness were measured in axial compression. Results. Only the highest cement dose used (24% fill, 7 mL on average) had an effect on mechanical stiffness or strength. Within this group, stiffness was improved relative to untreated fractures but not restored to prefracture levels, and strength was enhanced beyond intact values. These improvements in stiffness and strength depended significantly on bone density, with highly osteoporotic samples benefitting the least. Conclusion. Results suggest that highly osteoporotic patients may receive the least amount of improvement in mechanical properties after vertebroplasty. It is recommended, therefore, that cement volume be restricted to the amount needed for fracture reduction only because there may be a limit to the mechanical benefits that additional cement can offer, depending on patient bone density. Understanding these limitations can potentially minimize risks of adverse events.