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The Effect of Cement Augmentation on the Geometry and Structural Response of Recovered Osteopenic Vertebrae: An Anterior-Wedge Fracture Model

Alkalay, Ron N. PhD*; von Stechow, Dietrich MD*; Torres, Katherine ScM; Hassan, Serhan PhD; Sommerich, Robert PhD; Zurakowski, David PhD§

doi: 10.1097/BRS.0b013e31817cf7d1
Biomechanics

Study Design. The efficacy of cement augmentation in restoring the geometry and structural competence of failed thoracic and lumbar human vertebrae under mechanical loads was studied.

Objectives. To quantify whether cement augmentation restores and maintains the geometry and structural competence of failed osteopenic vertebrae and to assess the contribution of vertebral geometry to the achieved augmentation.

Summary of Background Data. Cement augmentation of failed vertebrae was clinically shown to alleviate significant pain and functional impairments associated with vertebral fragility fractures. However, the procedure’s efficacy in restoring the structural response of the failed vertebrae and maintaining the achieved geometry under functional loads remains unclear.

Methods. Nineteen thoracic and lumbar human vertebrae were tested to failure under compression-flexion loading. The vertebrae were allowed to recover, were retested to failure, augmented with Polymethylmethacrylate and again retested to failure. Repeated measures analysis was used to compare the change in vertebral geometry and structural response, defined as the multiplanar force and moment response of the vertebra to the imposed deformation, at each of the test stages. Linear regression was used to assess the role of the geometry of the failed vertebrae in affecting the outcome of augmentation.

Results. Augmentation significantly increased the compressive (228%) and flexion (118%) strength of the failed vertebrae and achieved a significant, albeit partial, restoration of vertebral geometry. However, the structural response of the failed vertebrae was markedly altered, whereas under applied loads, the achieved height restoration was significantly diminished. Although the geometry of the fractured vertebral body was associated with the degree of restoration of the vertebral body afteraugmentation, it was not correlated with the change in the structural parameters.

Conclusion. Augmentation increases the structural competence of failed vertebrae and to a degree, restores their geometry. However, the structural response of the augmented vertebrae was significantly modified. Furthermore, the augmented vertebrae were unable to maintain the degree of geometry restoration under load.

Augmentation of failed thoracolumbar vertebrae significantly restored their load carrying capacity and geometry. Under applied loads, however, the augmented vertebrae structural response was markedly changed compared with the intact vertebrae with the restoration of vertebral geometry largely diminished. Preaugmentation vertebral geometry was associated with the change in the geometry consequent to augmentation.

From the *Orthopedic Biomechanics Laboratory, Beth Israel Deaconess Medical Center; §Department of Biostatistics, Children’s Hospital, Boston; and †DePuy Acromed & Codman, Raynham, MA.

Acknowledgment date: June 16, 2004. First revision date: March 14, 2005. Second revision date: February 2, 2007. Third revision date: October 4, 2007. Acceptance date: October 4, 2007.

The manuscript submitted does not contain information about medical device(s)/drug(s).

Corporate/Industry funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.

Ron N. Alkalay and Dietrich von Stechow contributed equally to this work.

Address correspondence and reprint requests to Ron N. Alkalay, PhD, Orthopedic Biomechanics Laboratory, Beth Israel Deaconess Medical Center, 330 Brookline Avenue, Boston, MA 02215; E-mail: ralkalay@caregroup.harvard.edu

© 2008 Lippincott Williams & Wilkins, Inc.