Ex vivo biomechanical comparison of hydroxyapatite and polymethylmethacrylate cements for use with vertebroplasty

Abstract

Background and purpose: Little is known about the mechanical stabilization afforded by new materials proposed for use with vertebroplasty. This comparative ex vivo biomechanical study was designed to determine the strength and stiffness of osteoporotic vertebral bodies (VBs) subjected to compression fractures and stabilized with bipedicular injections of Cranioplastic altered in a manner consistent with the practice of vertebroplasty or BoneSource cement.

Methods: VBs T8-T10 and L2-L4 from 10 fresh spines were harvested from female cadavers (aged 91.5 years +/- 3.9 at death). These were screened for bone density (t score, -4.9 +/- 1.4; bone mineral density, 0.61 g/cm(2) +/- 0.19), disarticulated, and compressed to determine initial strength and stiffness. The fractured VBs were stabilized with bipedicular injections of a predetermined quantity and type of cement and then re-crushed.

Results: At both the thoracic and lumbar levels, VBs repaired with altered Cranioplastic resulted in significantly greater strength (P <.05) than that in their prefracture states, whereas those repaired with BoneSource were restored to their initial strength. Cranioplastic resulted in significantly stronger repairs than BoneSource in the thoracic region; however, repair strengths in the lumbar region were not significantly different. The repaired stiffness was significantly lower than the initial stiffness in all treatments and in both regions. Differences in the repaired stiffness between the treatment groups in either region and differences in the mechanical parameters obtained by adding an additional 2 mL of BoneSource were not significant.

Conclusion: Both materials in the volumes used either restored or increased VB strength, but none restored stiffness.

Figures

Fig 1.

Typical force-versus-deformation response curves for VB T9 compressed initially and after repair by using 6 mL of BoneSource.

Fig 2.

Radiographs of VB L2 injected with 6 mL of BoneSource (top), VB L3 injected with 8 mL of BoneSource (middle), and VB L4 injected with 6 mL of Cranioplastic opacified with barium sulfate (bottom).