• Sven Hoppe, Hoppe Sven, Yannick Loosli, Loosli Yannick, Daniel Baumgartner, Baumgartner Daniel, Paul Heini, Heini Paul, Lorin Benneker, and Benneker Lorin.
• *Department of Orthopaedic Surgery, Inselspital, University of Bern, Bern, Switzerland †RMS Foundation, Bettlach, Switzerland ‡Laboratory of Biomechanics, ETHZ, Zurich, Switzerland; and §Clinic Sonnenhof, Bern, Switzerland.
• Spine. 2014 Mar 15;39(6):E384-9.

Study DesignBiomechanical cadaveric study.ObjectiveTo determine whether augmentation positively influence screw stability or not.Summary Of Background DataImplantation of pedicle screws is a common procedure in spine surgery to provide an anchorage of posterior internal fixation into vertebrae. Screw performance is highly correlated to bone quality. Therefore, polymeric cement is often injected through specifically designed perforated pedicle screws into osteoporotic bone to potentially enhance screw stability.MethodsCaudocephalic dynamic loading was applied as quasi-physiological alternative to classical pull-out tests on 16 screws implanted in osteoporotic lumbar vertebrae and 20 screws in nonosteoporotic specimen. Load was applied using 2 different configurations simulating standard and dynamic posterior stabilization devices. Screw performance was quantified by measurement of screwhead displacement during the loading cycles. To reduce the impact of bone quality and morphology, screw performance was compared for each vertebra and averaged afterward.ResultsAll screws (with or without cement) implanted in osteoporotic vertebrae showed lower performances than the ones implanted into nonosteoporotic specimen. Augmentation was negligible for screws implanted into nonosteoporotic specimen, whereas in osteoporotic vertebrae pedicle screw stability was significantly increased. For dynamic posterior stabilization system an increase of screwhead displacement was observed in comparison with standard fixation devices in both setups.ConclusionAugmentation enhances screw performance in patients with poor bone stock, whereas no difference is observed for patients without osteoporosis. Furthermore, dynamic stabilization systems have the possibility to fail when implanted in osteoporotic bone.

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