title: Current modes of failure in TKA: infection, instability, and stiffness predominate.
abstract: BACKGROUND
  Historically, polyethylene wear and its sequelae (osteolysis, late instability, aseptic loosening) were common causes for revision total knee arthroplasty (TKA). Recently, polyethylene manufacturing has become more consistent; furthermore, a clearer understanding of the importance of oxidation on polyethylene performance led to packaging of the polyethylene bearings in an inert environment. This improved the quality and consistency of polyethylene used in TKA, raising the question of whether different failure modes now predominate after TKA.
  
  
  OBJECTIVE
  The purpose of this study was to determine the current reasons for (1) early and (2) late failures after TKA at one high-volume arthroplasty center.
  
  
  METHODS
  We reviewed all first-time revision TKAs performed between 2001 and 2011 at one institution, yielding a group of 253 revision TKAs in 251 patients. Mean age at the time of revision was 64 years (SD 10 years). Mean time to revision was 35 months (SD 23 months). Preoperative evaluations, laboratory data, radiographs, and intraoperative findings were used to determine causes for revision. Early failure was defined as revision within 2 years of the index procedure. The primary failure mechanism was determined by the operating surgeon.
  
  
  RESULTS
  Early failure accounted for 46% (116 of 253) of all revisions with infection (28 of 116 [24%]), instability (30 of 116 [26%]), and stiffness (21 of 116 [18%]) being the leading causes. Late failure accounted for 54% (137 of 253) of all revisions with the most common causes including infection (34 of 137 [25%]), instability (24 of 137 [18%]), and stiffness (19 of 253 [14%]). Polyethylene wear was implicated as the failure mechanism in 2% of early cases (two of 116) and 9% of late cases (13 of 137).
  
  
  CONCLUSIONS
  In contrast to previous studies, wear-related implant failure in TKA was relatively uncommon in this series. Changes in polyethylene manufacturing, sterilization, and storage may have accounted for some of this difference; however, longer-term followup will be required to verify this finding. Infection, instability, and stiffness represent the most common causes of early and late failure. Strategies to improve outcomes in TKA should be aimed at infection prophylaxis and treatment, surgical technique, and patient selection.
  
  
  METHODS
  Level III, therapeutic study. See Instructions for Authors for a complete description of levels of evidence.
authors.affiliation: Department of Orthopaedic Surgery, Stanford University Medical Center, 450 Broadway Street, Redwood, CA, 94063, USA, david.le@gmail.com.
authors.forename: David H
authors.initials: DH
authors.lastname: Le
authors.forename: Stuart B
authors.initials: SB
authors.lastname: Goodman
authors.forename: William J
authors.initials: WJ
authors.lastname: Maloney
authors.forename: James I
authors.initials: JI
authors.lastname: Huddleston
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects* / Q000295:instrumentation*; D001696:Biomechanical Phenomena; D002140:California; D019544:Equipment Failure Analysis; D005260:Female; D061847:Hospitals, High-Volume; D006801:Humans; D007593:Joint Instability / Q000175:diagnosis / Q000209:etiology* / Q000503:physiopathology / Q000601:surgery; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D007720:Knee Prosthesis / Q000009:adverse effects*; D008297:Male; D008875:Middle Aged; D020959:Polyethylene; D011474:Prosthesis Design; D011475:Prosthesis Failure; D016459:Prosthesis-Related Infections / Q000175:diagnosis / Q000209:etiology* / Q000382:microbiology / Q000601:surgery; D011859:Radiography; D016059:Range of Motion, Articular; D012086:Reoperation; D012307:Risk Factors; D013997:Time Factors; D016896:Treatment Outcome
chemical_list: D020959:Polyethylene