title: Current failure mechanisms after knee arthroplasty have changed: polyethylene wear is less common in revision surgery.
abstract: BACKGROUND
  The present study was designed to clarify which underlying indications can be currently considered the main reasons for failure after total knee arthroplasty as a function of time.
  
  
  METHODS
  We conducted a retrospective study that included all first revisions of total knee replacements during 2005 to 2010 at two high-volume arthroplasty centers. A revision was defined as the replacement of at least one prosthetic component. In the descriptive analysis, polyethylene wear, aseptic loosening, periprosthetic infection, malalignment, instability, arthrofibrosis, extensor mechanism deficiency, periprosthetic fracture, and retropatellar arthritis were given as the failure mechanism associated with an early, intermediate, or late time interval (less than one year, one to three years, and more than three years, respectively) after the index total knee arthroplasty.
  
  
  RESULTS
  Three hundred and fifty-eight revision total knee arthroplasties were included. Of those revisions, 19.8% were performed within the first year after the index arthroplasty. The most common indications for revision, besides aseptic loosening (21.8%), were instability (21.8%), malalignment (20.7%), and periprosthetic infection (14.5%). Revisions due to polyethylene wear (7%) rarely occurred. In the early failure group, the primary causes of revision were periprosthetic infection (26.8%) and instability (23.9%). In the intermediate group, instability (23.3%) and malalignment (29.4%) required revision surgery, whereas late failure mechanisms were aseptic loosening (34.7%), instability (18.5%), and polyethylene wear (18.5%).
  
  
  CONCLUSIONS
  Aseptic loosening, instability, malalignment, and periprosthetic infection continue to be the primary failure mechanisms leading to revision surgery. Contrary to previous literature, the results in the present study showed a substantial reduction in implant-associated revisions such as those due to polyethylene wear. Failure mechanisms that occur persistently early and in the intermediate term, such as periprosthetic infection, instability, and malalignment, remain common causes of revision surgery.
  
  
  METHODS
  Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.
authors.affiliation: Centrum für Muskuloskeletale Chirurgie Charite, Chariteplatz 1, 10117 Berlin, Germany. E-mail address for K. Thiele: Kathi.Thiele@charite.de. E-mail address for C. Perka: Carsten.Perka@charite.de.
authors.forename: Kathi
authors.initials: K
authors.lastname: Thiele
authors.affiliation: Centrum für Muskuloskeletale Chirurgie Charite, Chariteplatz 1, 10117 Berlin, Germany. E-mail address for K. Thiele: Kathi.Thiele@charite.de. E-mail address for C. Perka: Carsten.Perka@charite.de.
authors.forename: Carsten
authors.initials: C
authors.lastname: Perka
authors.affiliation: Waldkrankenhaus "Rudolf Elle," Klosterlausnitzer Straße 81, 07607 Eisenberg, Germany. E-mail address: G.Matziolis@krankenhaus-eisenberg.de.
authors.forename: Georg
authors.initials: G
authors.lastname: Matziolis
authors.affiliation: Operative Chirurgie München, Steinerstraße 6, 81369 München, Germany. E-mail address for H.O. Mayr: Hermann.Mayr@ocm-muenchen.de. E-mail address for M. Sostheim: Michael.Sostheim@ocm-muenchen.de. E-mail address for R. Hube: Robert.Hube@ocm-muenchen.de.
authors.forename: Hermann Otto
authors.initials: HO
authors.lastname: Mayr
authors.affiliation: Operative Chirurgie München, Steinerstraße 6, 81369 München, Germany. E-mail address for H.O. Mayr: Hermann.Mayr@ocm-muenchen.de. E-mail address for M. Sostheim: Michael.Sostheim@ocm-muenchen.de. E-mail address for R. Hube: Robert.Hube@ocm-muenchen.de.
authors.forename: Michael
authors.initials: M
authors.lastname: Sostheim
authors.affiliation: Operative Chirurgie München, Steinerstraße 6, 81369 München, Germany. E-mail address for H.O. Mayr: Hermann.Mayr@ocm-muenchen.de. E-mail address for M. Sostheim: Michael.Sostheim@ocm-muenchen.de. E-mail address for R. Hube: Robert.Hube@ocm-muenchen.de.
authors.forename: Robert
authors.initials: R
authors.lastname: Hube
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee; D017760:Bone Malalignment; D005260:Female; D006801:Humans; D007239:Infections / Q000209:etiology; D008297:Male; D008875:Middle Aged; D057068:Periprosthetic Fractures; D020959:Polyethylene; D011475:Prosthesis Failure / Q000209:etiology*; D012086:Reoperation; D012189:Retrospective Studies; D013997:Time Factors
chemical_list: D020959:Polyethylene