title: Effects of charité artificial disc on the implanted and adjacent spinal segments mechanics using a hybrid testing protocol.
abstract: METHODS
  Finite element model of L3-S1 segment and confirmatory cadaveric testing were used to investigate the biomechanical effects of a mobile core type artificial disc (Charité artificial disc; DePuy Spine, Raynham, MA) on the lumbar spine.
  
  
  OBJECTIVE
  To determine the effects of the Charité artificial disc across the implanted and adjacent segments.
  
  
  BACKGROUND
  Biomechanical studies of artificial discs that quantify parameters, like the load sharing and stresses, are sparse in the literature, especially for mobile-type core artificial disc designs. In addition, there is no standard protocol for studying the adjacent segmental effects of such implants.
  
  
  METHODS
  Human osteo-ligamentous spines (L1-S1) were tested before and after L5-S1 Charité artificial disc placement. The data were used to validate further an intact 3-dimensional (3-D) nonlinear L3-S1 finite element model. The model was subjected to 400-N axial compression and 10.6 Nm of flexion/extension pure moments (load control) or pure moments that produced the overall rotation of the L3-S1 Charité model equal to the intact case (hybrid approach). Resultant motion, load, and stress parameters were analyzed at the experimental and adjacent levels.
  
  
  RESULTS
  Finite element model validation was achieved only with the load-controlled experiments. The hybrid approach, believed to be more clinically relevant, revealed that Charité artificial disc leads to motion increases in flexion (19%) and extension (44%) at the L5-S1 level. At the instrumented level, the decrease in the facet loads was less than at the adjacent levels; the corresponding decrease being 26% at L3-L4, 25% at L4-L5, and 13.4% at L5-S1 when compared to the intact. Intradiscal pressure changes in the L4-L5 and L3-L4 segments were minimal. Shear stresses at the Charité artificial disc-L5 endplate interface were higher than those at S1 interface. However, in the load control mode, the increase in facet loads in extension was approximately 14%, as compared to the intact case.
  
  
  CONCLUSIONS
  The hybrid testing protocol is advocated because it better reproduces clinical observations in terms of motion following surgery, using pure moments. Using this approach, we found that the Charité artificial disc placement slightly increases motion at the implanted level, with a resultant increase in facet loading when compared to the adjacent segments, while the motions and loads decrease at the adjacent levels. However, in the load control mode that we believe is not that clinically relevant, there was a large increase in motion and a corresponding increase in facet loads, as compared to the intact.
authors.affiliation: Spine Research Center, University of Toledo and Medical University of Ohio, Toledo, OH 43606, USA. vijay.goel@utoledo.edu
authors.forename: Vijay K
authors.initials: VK
authors.lastname: Goel
authors.forename: Jonathan N
authors.initials: JN
authors.lastname: Grauer
authors.forename: Tushar Ch
authors.initials: TCh
authors.lastname: Patel
authors.forename: Ashok
authors.initials: A
authors.lastname: Biyani
authors.forename: Koichi
authors.initials: K
authors.lastname: Sairyo
authors.forename: Srilakshmi
authors.initials: S
authors.lastname: Vishnubhotla
authors.forename: Aaron
authors.initials: A
authors.lastname: Matyas
authors.forename: Ian
authors.initials: I
authors.lastname: Cowgill
authors.forename: Miranda
authors.initials: M
authors.lastname: Shaw
authors.forename: Rebecca
authors.initials: R
authors.lastname: Long
authors.forename: David
authors.initials: D
authors.lastname: Dick
authors.forename: Manohar M
authors.initials: MM
authors.lastname: Panjabi
authors.forename: Hassan
authors.initials: H
authors.lastname: Serhan
mesh_terms: D001696:Biomechanical Phenomena / Q000379:methods / Q000592:standards*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D020007:Implants, Experimental / Q000592:standards*; D007403:Intervertebral Disc / Q000502:physiology* / Q000601:surgery; D008159:Lumbar Vertebrae / Q000502:physiology* / Q000601:surgery; D008954:Models, Biological; D016474:Weight-Bearing / Q000502:physiology