The biomechanics of vertebroplasty - The effect of cement volume on mechanical behavior

Study Design. Ex vivo biomechanical study using osteoporotic cadaveric vert ebral bodies. Objective. To determine the association between the volume of cement inject ed during percutaneous vertebroplasty and the restoration of strength and s tiffness in osteoporotic vertebral bodies, two investigational cements were studied: Orthocomp (Orthovita, Malvern, PA) and Simplex 20 (Simplex P with 20% by weight barium sulfate content; Stryker-Howmedica-Osteonics, Rutherf ord, NJ). Summary of Background Data. Previous biomechanical studies have shown that injections of 8-10 mL of cement during vertebroplasty restore or increase v ertebral body strength and stiffness; however, the dose-response associatio n between cement volume and restoration of strength and stiffness is unknow n. Methods. Compression fractures were experimentally created in 144 vertebral bodies (T6-L5) obtained from 12 osteoporotic spines harvested from female cadavers. After initial strength and stiffness were determined, the vertebr al bodies were stabilized using bipedicular injections of cement totaling 2 , 4, 6, or 8 mL and recompressed, after which post-treatment strength and s tiffness Were measured. Strength and stiffness were considered restored whe n post-treatment values were not significantly different from initial value s. Results. Strength was restored for all regions when 2 mt of either cement w as injected. To restore stiffness with Orthocomp, the thoracic and thoracol umbar regions required 4 mt, but the lumbar region required 6 mL. To restor e stiffness with Simplex 20, the thoracic and lumbar regions required 4 mL, but the thoracolumbar region required 8 mL. Conclusion. These data provide guidance on the ce ment volumes needed to re store biomechanical integrity to com pressed osteoporotic vertebral bodies.