title: The biomechanics of pedicle screw augmentation with cement.
abstract: BACKGROUND
  A persistent challenge in spine surgery is improving screw fixation in patients with poor bone quality. Augmenting pedicle screw fixation with cement appears to be a promising approach.
  
  
  OBJECTIVE
  The purpose of this study was to survey the literature and assess the previous biomechanical studies on pedicle screw augmentation with cement to provide in-depth discussions of the biomechanical benefits of multiple parameters in screw augmentation.
  
  
  METHODS
  This is a systematic literature review.
  
  
  METHODS
  A search of Medline was performed, combining search terms of pedicle screw, augmentation, vertebroplasty, kyphoplasty, polymethylmethacrylate, calcium phosphate, or calcium sulfate. The retrieved articles and their references were reviewed, and articles dealing with biomechanical testing were included in this article.
  
  
  RESULTS
  Polymethylmethacrylate is an effective material for enhancing pedicle screw fixation in both osteoporosis and revision spine surgery models. Several other calcium ceramics also appear promising, although further work is needed in material development. Although fenestrated screw delivery appears to have some benefits, it results in similar screw fixation to prefilling the cement with a solid screw. Some differences in screw biomechanics were noted with varying cement volume and curing time, and some benefits from a kyphoplasty approach over a vertebroplasty approach have been noted. Additionally, in cadaveric models, cemented-augmented screws were able to be removed, albeit at higher extraction torques, without catastrophic damage to the vertebral body. However, there is a risk of cement extravasation leading to potentially neurological or cardiovascular complications with cement use. A major limitation of these reviewed studies is that biomechanical tests were generally performed at screw implantation or after a limited cyclic loading cycle; thus, the results may not be entirely clinically applicable. This is particularly true in the case of the bioactive calcium ceramics, as these biomechanical studies would not have measured the effects of osseointegration.
  
  
  CONCLUSIONS
  Polymethylmethacrylate and various calcium ceramics appear promising for the augmentation of pedicle screw fixation biomechanically in both osteoporosis and revision spine surgery models. Further translational studies should be performed, and the results summarized in this review will need to be correlated with the clinical outcomes.
authors: Department of Neurosurgery, The Johns Hopkins University School of Medicine, 1800 Orleans St, Baltimore, MD 21287, USA. Electronic address: belder4@jhmi.edu.
authors: Benjamin D
authors: BD
authors: Elder
authors: Department of Neurosurgery, The Johns Hopkins University School of Medicine, 1800 Orleans St, Baltimore, MD 21287, USA.
authors: Sheng-Fu L
authors: SF
authors: Lo
authors: Department of Neurosurgery, The Johns Hopkins University School of Medicine, 1800 Orleans St, Baltimore, MD 21287, USA.
authors: Christina
authors: C
authors: Holmes
authors: Department of Neurosurgery, The Johns Hopkins University School of Medicine, 1800 Orleans St, Baltimore, MD 21287, USA.
authors: Courtney R
authors: CR
authors: Goodwin
authors: Department of Neurosurgery, The Johns Hopkins University School of Medicine, 1800 Orleans St, Baltimore, MD 21287, USA.
authors: Thomas A
authors: TA
authors: Kosztowski
authors: Department of Neurosurgery, The Johns Hopkins University School of Medicine, 1800 Orleans St, Baltimore, MD 21287, USA.
authors: Ioan A
authors: IA
authors: Lina
authors: Department of Neurosurgery, The Johns Hopkins University School of Medicine, 1800 Orleans St, Baltimore, MD 21287, USA.
authors: John E
authors: JE
authors: Locke
authors: Department of Neurosurgery, The Johns Hopkins University School of Medicine, 1800 Orleans St, Baltimore, MD 21287, USA.
authors: Timothy F
authors: TF
authors: Witham
mesh_terms: D001696:Biomechanical Phenomena; D001843:Bone Cements; D001863:Bone Screws; D002130:Calcium Phosphates; D006801:Humans; D010024:Osteoporosis / Q000601:surgery; D065289:Pedicle Screws; D019904:Polymethyl Methacrylate; D013131:Spine / Q000601:surgery*
chemical_list: D001843:Bone Cements; D002130:Calcium Phosphates; D019904:Polymethyl Methacrylate; C020243:calcium phosphate
keywords: Biomechanics; Cement; Kyphoplasty; Pedicle screw augmentation; Polymethylmethacrylate; Proximal junction kyphosis; Vertebroplasty