The effect of cement augmentation on the geometry and structural response of recovered osteopenic vertebrae: an anterior-wedge fracture model.

Abstract

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