title: A unique modular implant system enhances load sharing in anterior cervical interbody fusion: a finite element study.
abstract: BACKGROUND
  The efficacy of dynamic anterior cervical plates is somewhat controversial. Screws in static-plate designs have a smaller diameter and can cut through bone under load. While not ideal, this unintended loosening can help mitigate stress shielding. Stand-alone interbody devices with integral fixation have large endplate contact areas that may inhibit or prevent loosening of the fixation. This study investigates the load sharing ability of a novel dynamic plate design in preventing the stress shielding of the graft material compared to the non-dynamic devices.
  
  
  METHODS
  An experimentally validated intact C5-C6 finite element model was modified to simulate discectomy and accommodate implant-graft assembly. Four implant iterations were modeled; InterPlate titanium device with dynamic surface features (springs), InterPlate titanium non-dynamic device, InterPlate titanium design having a fully enclosed graft chamber, and the InterPlate design in unfilled PEEK having a fully enclosed graft chamber. All the models were fixed at the inferior-most surface of C6 and the axial displacement required to completely embed the dynamic surface features was applied to the model.
  
  
  RESULTS
  InterPlate device with dynamic surface features induced higher graft stresses compared to the other design iterations resulting in uniform load sharing. The distribution of these graft stresses were more uniform for the InterPlate dynamic design.
  
  
  CONCLUSIONS
  These results indicate that the dynamic design decreases the stress shielding by increasing and more uniformly distributing the graft stress. Fully enclosed graft chambers increase stress shielding. Lower implant material modulus of elasticity does not reduce stress shielding significantly.
authors.forename: Vivek
authors.initials: V
authors.lastname: Palepu
authors.forename: Ali
authors.initials: A
authors.lastname: Kiapour
authors.affiliation: Engineering Center for Orthopaedic Research Excellence (E-CORE), Departments of Bioengineering and Orthopaedic Surgery, Colleges of Engineering and Medicine, University of Toledo, Toledo, OH 43606, USA. Vijay.Goel@utoledo.edu.
authors.forename: Vijay K
authors.initials: VK
authors.lastname: Goel
authors.forename: James M
authors.initials: JM
authors.lastname: Moran
mesh_terms: D001698:Biomedical Engineering / Q000379:methods; D001860:Bone Plates; D016025:Bone Transplantation; D002574:Cervical Vertebrae / Q000473:pathology; D004548:Elasticity; D004867:Equipment Design; D020342:Finite Element Analysis; D006801:Humans; D016268:Internal Fixators; D019736:Prostheses and Implants; D013123:Spinal Fusion / Q000379:methods*; D013314:Stress, Mechanical; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry; D016474:Weight-Bearing
chemical_list: D014025:Titanium