The effect of vertebral body percentage fill on mechanical behavior during percutaneous vertebroplasty

Study Design. An ex vivo biomechanical study was conducted using osteoporotic cadaveric vertebral bodies. Objective. To determine the relationship between the percentage of osteoporotic vertebral body volume filled with polymethylmethacrylate cement during percutaneous vertebroplasty and the percentage restoration of strength and stiffness. Summary of Background Data. A previous biomechanical study reported a weak relationship between the volume of cement injected and restoration of vertebral body strength and stiffness. Vertebral bodies vary considerably in size among regions and among spines, and the weak correlation may be attributed to the fact that the volume of vertebral bodies was note explicitly considered. Methods. The volume of 120 vertebral bodies (T6-L5) harvested from 10 osteoporotic female cadaver spines was determined by Archimedean displacement. Compression fractures were experimentally created, and initial strength and stiffness were determined. The vertebral bodies were stabilized using bipedicular injections of 2-8 mL of cement and then recompressed, after which post-treatment strength and stiffness were measured. Linear regression was used to analyze the relationship between percentage of volume fill and percentage of restored stiffness and strength. Results. The correlations between percentage of fill and restored strength and stiffness were weak: r(2)=0.21 and r(2)=0.27, respectively. On average, restoration of strength and stiffness required vertebral body cement fills of 16.2% and 29.8%, respectively. Conclusion. Strength and stiffness are weakly correlated with the percentage fill volume of cement injected during vertebroplasty.