Effect of cement volume on the strength and stiffness of vertebral bodies after vertebroplasty: Ex vivo evaluation

Background: Studies have reported that small fill volumes of different cements can restore the strength and stiffness of fractured vertebral bodies and prevent cement extravasation during vertebroplasty. We investigated the biomechanical results of specific volumes of cement injected into fractured thoracic, thoracolumbar, and lumbar vertebral bodies and evaluated the relationship between bone mineral density and the strength and stiffness of the vertebral body. Methods: Compression fractures were created in 52 vertebrae (T5-L5) obtained from four cadaveric spines. The initial bone mineral density of each vertebral body was measured with dual-energy X-ray absorptiometry; also measured were initial strength and stiffness. Bipedicular repair was then performed using 2 mL of polymethylmethacrylate cement in thoracic vertebral bodies, 4 mL in thoracolumbar vertebral bodies, and 6 mL in lumbar vertebral bodies. After recompression, strength and stiffness were measured again. Pretreatment and posttreatment values were analyzed statistically. Results: Bone mineral density was strongly correlated with the strength and stiffness of intact vertebral bodies. Strength and stiffness were restored in all vertebral bodies by using the volumes specified for each spinal region. Strength increased significantly (paired t-tests, all P < 0.05) by 32% in the thoracic region, by 50% in the thoracolumbar region, and by 33% in the lumbar region, compared with initial values. Stiffness did not significantly change before and after treatment in any of the vertebral regions. Conclusions: These data may help provide a clinical guideline for cement fill volumes for the restoration of the mechanical integrity of osteoporotic vertebrae after compression fractures.