The Biomechanics of Vertebroplasty

The Effect of Cement Volume on Mechanical Behavior

Abstract

Study Design. 

Ex vivo biomechanical study using osteoporotic cadaveric vertebral bodies.

Objective. 

To determine the association between the volume of cement injected during percutaneous vertebroplasty and the restoration of strength and stiffness 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, Rutherford, NJ).

Summary of Background Data. 

Previous biomechanical studies have shown that injections of 8–10 mL of cement during vertebroplasty restore or increase vertebral body strength and stiffness; however, the dose–response association between cement volume and restoration of strength and stiffness is unknown.

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 vertebral bodies were stabilized using bipedicular injections of cement totaling 2, 4, 6, or 8 mL and recompressed, after which post-treatment strength and stiffness were measured. Strength and stiffness were considered restored when post-treatment values were not significantly different from initial values.

Results. 

Strength was restored for all regions when 2 mL of either cement was injected. To restore stiffness with Orthocomp, the thoracic and thoracolumbar regions required 4 mL, but the lumbar region required 6 mL. To restore 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 cement volumes needed to restore biomechanical integrity to compressed osteoporotic vertebral bodies.