title: Wear damage in mobile-bearing TKA is as severe as that in fixed-bearing TKA.
abstract: BACKGROUND
  Mobile-bearing TKAs reportedly have no clinical superiority over fixed-bearing TKAs, but a potential benefit is improved polyethylene wear behavior.
  
  
  OBJECTIVE
  We asked whether extent of damage and wear patterns would be less severe on retrieved mobile-bearing TKAs than on fixed-bearing TKAs and if correlations with patient demographics could explain differences in extent or locations of damage.
  
  
  METHODS
  We performed damage grading and mapping of 48 mobile-bearing TKAs retrieved due to osteolysis/loosening, infection, stiffness, instability or malpositioning. Visual grading used stereomicroscopy to identify damage, and a grade was assigned based on extent and severity. Each damage mode was then mapped onto a photograph of the implant surface, and the area affected was calculated.
  
  
  RESULTS
  Marked wear damage occurred on both surfaces, with burnishing, scratching, and pitting the dominant modes. Damage occurred over a large portion of both surfaces, exceeding the available articular borders in nearly 30% of implants. Wear of mobile-bearing surfaces included marked third-body debris. Damage on tibiofemoral and mobile-bearing surfaces was not correlated with patient BMI or component alignment. Damage on mobile-bearing surfaces was positively correlated with length of implantation and was greater in implants removed for osteolysis or instability than in those removed for stiffness or infection.
  
  
  CONCLUSIONS
  Each bearing surface in mobile-bearing implants was damaged to an extent similar to that in fixed-bearing implants, making the combined damage score higher than that for fixed-bearing implants. Mobile-bearing TKAs did not improve wear damage, providing another argument against the superiority of these implants over fixed-bearing implants.
authors.affiliation: Department of Biomechanics, Hospital for Special Surgery, 535 East 70th Street, New York, NY 10021, USA.
authors.forename: Natalie H
authors.initials: NH
authors.lastname: Kelly
authors.forename: Rose H
authors.initials: RH
authors.lastname: Fu
authors.forename: Timothy M
authors.initials: TM
authors.lastname: Wright
authors.forename: Douglas E
authors.initials: DE
authors.lastname: Padgett
mesh_terms: D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects / Q000295:instrumentation*; D001696:Biomechanical Phenomena; D020878:Device Removal; D006801:Humans; D007593:Joint Instability / Q000209:etiology; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D007720:Knee Prosthesis; D016014:Linear Models; D008855:Microscopy, Electron, Scanning; D009519:New York City; D010014:Osteolysis / Q000209:etiology; D020959:Polyethylene; D011474:Prosthesis Design; D011475:Prosthesis Failure; D016459:Prosthesis-Related Infections / Q000209:etiology; D011859:Radiography; D012042:Registries; D012086:Reoperation; D012720:Severity of Illness Index; D013052:Spectrometry, X-Ray Emission; D013314:Stress, Mechanical; D013499:Surface Properties; D013997:Time Factors; D016896:Treatment Outcome
chemical_list: D020959:Polyethylene