The influence of endplate-to-endplate cement augmentation on vertebral strength and stiffness in vertebroplasty.

Methods: Controlled in vitro trial. Objective: To study vertebral strength in relation to cement augmentation technique after vertebroplasty and to assess the influence of the biomechanical compression model on postoperative results.

Background: In the treatment of osteoporotic vertebral fractures, the role of vertebroplasty has been well established. Biomechanical compression models thus far used, compressing vertebrae by only 25% of their initial height, did not show a correlation between cement augmentation volumes and postoperative compression strength. In these studies, even very small volumes of cement seem effective. However, these models may not realistically simulate clinically relevant osteoporotic wedge fractures. We hypothesize that, in clinically relevant osteoporotic wedge fractures, postoperative vertebral body strength is strongly dependent on endplate-to-endplate cement augmentation.

Methods: Twenty-five intact osteoporotic cadaver vertebrae were obtained (10 lumbar, 15 thoracic). In 21 vertebrae, anterior wedge fractures (AO type A1.2) were created by controlled external force, with preset height reduction by 35%. After height reconstruction, 9 vertebrae were augmented endplate-to-endplate and 12 vertebrae were partially augmented with polymethylmethacrylate (PMMA). Another 4 vertebrae were compressed by only 25%. Posttreatment strength and stiffness of the vertebrae were determined by a compression test identical to the pretreatment compression protocol.

Results: In the 35% compression group, posttreatment strength was significantly decreased in vertebrae that were partially augmented with cement compared with the endplate-to-endplate augmented group (767 +/- 257 N vs. 1141 +/- 325 N, P < 0.01). Postoperative strength amounted 106% +/- 27% of preoperative strength values in the endplate-to-endplate augmented vertebrae, compared with 65% +/- 18% in the partially augmented vertebrae (P < 0.001). In the 25% compression group, results in height restored and augmented vertebrae were similar to the nontreated vertebrae.

Conclusions: Endplate-to-endplate PMMA augmentation restores the biomechanical properties of vertebrae in clinically relevant anterior wedge fractures. Our preliminary data suggest that biomechanical models with only 25% compressive deformation unlikely form a good model to assess the mechanical effects of cement augmentation in osteoporotic fractures.