title: What is the correlation of in vivo wear and damage patterns with in vitro TDR motion response?
abstract: METHODS
  This study combined the evaluation of retrieved total disc replacements (TDRs) with a biomechanical study using human lumbar spines. Thirty-eight CHARITE TDRs were retrieved from 32 patients after 7.3 years average implantation. All implants were removed because of intractable back pain and/or facet degeneration. In parallel, 20 new implants were evaluated at L4-L5 and L5-S1 in an in vitro lumbar spine model.
  
  
  OBJECTIVE
  The purpose of this study was to correlate wear and damage patterns in retrieved TDRs with motion patterns observed in an in vitro lumbar spine model. We also sought to determine whether one-sided wear and motion patterns were associated with greater in vivo wear.
  
  
  BACKGROUND
  The comparison of polyethylene wear in TDRs after long-term implantation to those tested using an in vitro model had not yet been investigated.
  
  
  METHODS
  The wear patterns of each retrieved PE core was analyzed at the rim and dome. Thirty-five cores were further analyzed using MicroCT to determine the penetration symmetry. For the in vitro study the implants were tested under physiologic loads using a validated cadaveric model. Motion patterns of the in vitro-tested implants were tracked using sequential video-fluoroscopy.
  
  
  RESULTS
  Fifteen of 35 retrieved cores (43%) displayed one-sided wear patterns. Significant correlations were observed between implantation time and penetration and penetration rate. In the in vitro study, there was evidence of motion at both articulations, motion at both articulation but predominantly at the top articulation, and solelyat the top articulation. Core entrapment and pinching was observed and associated with visual evidence of core bending or deformation.
  
  
  CONCLUSIONS
  This is the first study to directly compare the long-term PE wear and damage mechanisms in TDR retrievals with the motion patterns generated by a validated in vitro cadaveric testing model. The retrievals exhibited wear patterns consistent with the in vitro testing.
authors.affiliation: Implant Research Center, School of Biomedical Engineering, Science, Drexel University, Philadelphia, PA, USA. skurtz@drexel.edu
authors.forename: Steven M
authors.initials: SM
authors.lastname: Kurtz
authors.forename: Avinash
authors.initials: A
authors.lastname: Patwardhan
authors.forename: Daniel
authors.initials: D
authors.lastname: MacDonald
authors.forename: Lauren
authors.initials: L
authors.lastname: Ciccarelli
authors.forename: André
authors.initials: A
authors.lastname: van Ooij
authors.forename: Mark
authors.initials: M
authors.lastname: Lorenz
authors.forename: Michael
authors.initials: M
authors.lastname: Zindrick
authors.forename: Patrick
authors.initials: P
authors.lastname: O'Leary
authors.forename: Jorge
authors.initials: J
authors.lastname: Isaza
authors.forename: Raymond
authors.initials: R
authors.lastname: Ross
mesh_terms: D000328:Adult; D000368:Aged; D001696:Biomechanical Phenomena; D020878:Device Removal; D017586:Diskectomy / Q000295:instrumentation*; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007405:Intervertebral Disc Displacement / Q000601:surgery*; D008159:Lumbar Vertebrae / Q000502:physiology / Q000601:surgery*; D008297:Male; D008422:Materials Testing; D008875:Middle Aged; D009068:Movement; D020959:Polyethylene; D019736:Prostheses and Implants; D011475:Prosthesis Failure
chemical_list: D020959:Polyethylene