title: In vivo functional performance of failed Prodisc-L devices: retrieval analysis of lumbar total disc replacements.
abstract: METHODS
  A retrieval analysis of wear modes and fixation of lumbar total disc replacements (TDRs). Explanted Prodisc-L TDRs were prospectively collected during a 7-year period (2005-2011) and analyzed.
  
  
  OBJECTIVE
  To assess the in vivo modes of wear and fixation of lumbar TDR with the Prodisc-L device.
  
  
  BACKGROUND
  Inferior clinical outcomes and failure of lumbar TDR may occur because of suboptimal component fixation, wear properties, and impingement in a subset of patients. Posterior component TDR impingement has been demonstrated radiographically; however, despite its widespread use, the in vivo mechanical performance and fixation of the Prodisc-L device remain unknown.
  
  
  METHODS
  Explanted polyethylene and metallic (CoCrMo) components of Prodisc-L devices were examined by light stereo-microscopy (6X-31X), scanning electron microscopy, and energy-dispersive x-ray analysis from an international retrieval registry, with 13 participating surgeons.
  
  
  RESULTS
  Nineteen ProDisc-L devices from 18 patients (age, 44.7 ± 2.9 yr) following an index TDR at L4-L5 (n = 6), L5-S1 (n = 11), and unknown level (n = 2) were explanted for pain (n = 8), prosthesis subluxation/migration (n = 4), end plate collapse/subsidence (n = 3), polyethylene dislodgement (n = 3), and unknown (n = 2) after a mean length of implantation of 13.0 ± 3.9 months. Surface area of bony ongrowth was 9.6 ± 2.9% (range, 0%-52.5%). TDR burnishing was observed posteriorly consistent with component impingement in extension in 53% (8/15) (P < 0.02), more commonly than anterior 20% (3/15) lateral 20% (n = 3) (3/15) patterns. Circumferential burnishing was not observed. Posterior impingement was associated with 6° lordotic implants (P < 0.05) and 10-mm polyethylene size (P < 0.05). Backside wear occurred in 75% (9 of 12) of the disassembled implants and third-body wear was observed in 33% (5 of 15).
  
  
  CONCLUSIONS
  Metallic end plate burnishing was evident in a large percentage of clinically failed Prodisc-L TDR devices, most commonly posteriorly, consistent with impingement in extension. Long-term follow-up studies will evaluate the effects of the observed backside wear, third-body wear, and end plate impingement on clinical outcomes.
authors.affiliation: Hospital for Special Surgery, The Spine Care Institute, New York, NY 10021, USA. drlebl@alumni.stanford.edu
authors.forename: Darren R
authors.initials: DR
authors.lastname: Lebl
authors.forename: Frank P
authors.initials: FP
authors.lastname: Cammisa
authors.forename: Federico P
authors.initials: FP
authors.lastname: Girardi
authors.forename: Timothy
authors.initials: T
authors.lastname: Wright
authors.forename: Celeste
authors.initials: C
authors.lastname: Abjornson
mesh_terms: D000328:Adult; D019299:Decompression, Surgical; D020878:Device Removal; D004868:Equipment Failure; D005260:Female; D017276:Friction; D006801:Humans; D007403:Intervertebral Disc / Q000601:surgery*; D008159:Lumbar Vertebrae / Q000601:surgery*; D008297:Male; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D008875:Middle Aged; D011446:Prospective Studies; D019736:Prostheses and Implants / Q000009:adverse effects*; D011475:Prosthesis Failure; D059145:Total Disc Replacement / Q000295:instrumentation*; D016474:Weight-Bearing