AUGMENTATION OF PEDICLE SCREW FIXATION IN THE OSTEOPOROTIC LUMBAR SPINE

摘要

Pedicle screw fixation is problematic in osteoporotic bone and is dependent on the screw-bone interface. Although augmentation with polymethylmethacrylate (PMMA) can result in an improved mechanical construct, there are risks for cement extrusion. This study examined the level of augmentation on the failure strength of the screw-bone interface. Thirty-six osteoporotic lumbar vertebrae were equally divided into three groups. To examine screw-bone interface, the three groups varied by the amount of screw-bone surface augmentation (0, 50, 100%). Each screw was tested for tensile pullout strength. Group differences in maximum pullout strength were examined with ANOVA and regression analyses. Significant differences in pullout strength occurred between the augmented and non-augmented groups. There was no significant difference between the two augmentation groups. There was no correlation between the BMD of the osteoporotic vertebrae and pullout strength for any group. The pullout strength of the two augmentation groups were similar to the pullout strengths reported in the literature for nonosteoporotic bone. Therefore, augmentation can achieve an adequate level of strength without a complete cement mantle surrounding the screw-bone interface. There are theoretical advantages of shorter operative time and reduced risk of extrusion with a less than complete cement mantle.