Review ArticleThe biomechanics of pedicle screw augmentation with cement
Introduction
An increasing challenge in spinal surgery has been the need to achieve optimal fixation of the pedicle screws in cases with poor bone quality such as in osteoporosis and previously radiated spinal levels. Additionally, revision surgeries to correct previously failed instrumentation are progressively more common. Therefore, techniques to enhance the fixation of pedicle screws are required, and a primary method for this has been to augment the screw fixation with cement. Although polymethylmethacrylate (PMMA) has been approved by the US Food and Drug Administration for the treatment of osteoporotic and tumor-related compression fractures, it has not been approved for pedicle screw augmentation, and this technique is currently used off-label.
The objective of this article was to review the studies assessing the biomechanical properties of pedicle screw cement augmentation in humans, with a specific focus on use in osteoporosis and revision spine cases. In-depth discussions of biomechanical testing methods, fenestrated screws, cement volume, cement curing time, cement material, augmented screw failure modalities, cementing technique, cementing complications, and the biomechanical effects on the vertebral bodies are also provided.
Section snippets
Materials and methods
A comprehensive search was conducted using Medline with an attempt to identify all the relevant studies documenting biomechanical testing in human tissues on cement augmentation of pedicle screws. A Medline search was conducted using the search terms “pedicle screw” combined with “augmentation,” OR “vertebroplasty,” OR “kyphoplasty,” OR “PMMA,” OR “polymethylmethacrylate,” OR “Calcium phosphate,” or “Calcium sulfate” from January 1, 1970 to September 30, 2014 as cement augmentation of pedicle
Results
Using the search strategy described previously, 306 articles were identified. As this systematic review targeted studies on cement augmentation biomechanics in human spines, studies with only clinical data and biomechanical studies performed in animals with different vertebral anatomy were excluded. Additionally, studies only providing modeling data were not included in the analysis as they were based on previous biomechanical work and would therefore be redundant. Following this search
Discussion
To the best of our knowledge, this is the first article to systematically review the biomechanics literature on cement augmentation of lumbosacropelvic posterior screw fixation. Based on this review, PMMA and several calcium ceramic materials appear to be effective materials for enhancing pedicle screw fixation in both osteoporosis and revision spine surgery models.
The biomechanical properties of screw fixation are primarily tested using two methods: axial pullout testing and cyclic
Conclusions
Polymethylmethacrylate, along with several calcium ceramic materials, are effective materials for enhancing pedicle screw fixation in both osteoporosis and revision spine surgery models. However, a major limitation of these biomechanical studies to date is that the tests were performed at screw implantation or after a limited cyclic loading cycle; thus, the results may not be entirely clinically applicable. Further translational studies should thus be performed, and the results summarized in
Acknowledgments
This article reflects the views of the authors and should not be construed to represent the views or policies of the United States Food and Drug Administration. Although no funding was provided for this project, the senior author (TFW) receives research support from Eli Lilly & Co., The Johns Hopkins Neurological Pain Research Institute, and the Gordon and Marilyn Macklin Foundation.
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FDA device/drug status: Not approved for this indication: pedicle screw augmentation with polymethylmethacrylate or other cements.
Author disclosures: BDE: Other: Funding from NS/AANS Section on Disorders of the Spine and Peripheral Nerves (C). S-FLL: Nothing to disclose. CH: Nothing to disclose. CRG: Nothing to disclose. TAK: Nothing to disclose. IAL: Nothing to disclose. JEL: Nothing to disclose. TFW: Grant: Eli Lilly and Co. (B), The Gordon and Marilyn Macklin Foundation (F); Other: Operation Backbone (Advisory board member for this nonprofit organization).
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