Effect of augmentation on the mechanics of vertebral wedge fractures

Study Design. The effect of cement augmentation of wedge-fractured vertebral bodies on spine segment compliance was studied in 16 cadaver specimens. Objectives. 1) To assess the mechanical effects of cement augmentation of vertebral wedge fractures. 2) To determine whether a new reduction/injection procedure has the same mechanical effects as the established direct injection procedure. Summary of Background Data. Although wedge fractures cause pain and disability in hundreds of thousands of people, few effective treatments are available. Clinical studies have shown that cement augmentation, a new procedure, effectively relives pain and restores mobility in patients suffering from weak or fractured vertebrae. However, only a few studies have examined the mechanics of vertebral augmentation. Methods. A wedge fracture was created in the middle vertebra of 16 three-vertebra cadaver spine segments. Neutral and full-load compliance of each fractured spine segment in flexion/extension and lateral bending were assessed by measuring the relative rotation of the vertebral bodies in response to applied moments. Eight of the fractured vertebral bodies were then augmented using direct injection, while the remaining eight fractured vertebral bodies were augmented using a combined reduction/injection procedure. Compliance of the augmented segments was then assessed. Results. Augmentation significantly reduced the neutral compliance (reduction of 25% +/- 23%) (mean +/- standard deviation) and the full-load compliance (reduction of 23% +/- 20%) in flexion/extension (P < 0.005). Augmentation also significantly reduced the neutral compliance (reduction of 34% +/- 20%) and the full-load compliance (reduction of 26% +/- 17%) in lateral bending (P < 0.0001). No significant difference was found between the two procedures for compliance reduction. Conclusions. Augmentation of wedge fractures using both direct injection and reduction/injection reduces spine segment compliance significantly.