title: Poor Acetabular Component Orientation Increases Revision Risk in Metal-on-Metal Hip Arthroplasty.
abstract: The rate of and the reasons for the failure of metal-on-metal (MoM) bearings have recently been discussed in literature. The aim of this study was to evaluate the influence of acetabular cup inclination and version angles on revision risk in patients with MoM hip arthroplasty.
  
  
  
  We retrospectively reviewed 825 patients (976 hips) who underwent a MoM hip arthroplasty between 2000 and 2013. There were 474 men and 351 women, with a mean age of 58 (19-86) years. Acceptable cup orientation was considered to be inside the Lewinnek's safe zone.
  
  
  
  The mean acetabular inclination angle was 48.9° (standard deviation, 8.1°; range, 16°-76°) and version angle 20.6° (standard deviation, 9.9°; range, -25 to 46°). The cup was found to be outside the Lewinnek's safe zone in 571 hips (58.5%). Acetabular cup revision surgery was performed in 157 hips (16.1%). The cup angles were outside Lewinnek's safe zone in 69.2% of the revised hips. The mean interobserver reliability and intraobserver repeatability of the measurements of cup inclination and version angles were excellent (intraclass correlation coefficients >0.90). The odds ratio for revision in hips outside vs inside the Lewinnek's safe zone was 1.82 (95% confidence interval, 1.26-2.62; P = .0014).
  
  
  
  Our findings provide compelling evidence that a cup position outside the Lewinnek's safe zone is associated with increased revision risk in patients with MoM arthroplasty.
authors.affiliation: Division of Orthopaedic and Trauma Surgery, Department of Surgery, Oulu University Hospital, Medical Research Center, University of Oulu, Oulu, Finland.
authors.forename: Tuomas J T
authors.initials: TJT
authors.lastname: Tauriainen
authors.affiliation: Division of Orthopaedic and Trauma Surgery, Department of Surgery, Oulu University Hospital, Medical Research Center, University of Oulu, Oulu, Finland.
authors.forename: Tuukka T
authors.initials: TT
authors.lastname: Niinimäki
authors.affiliation: Department of Diagnostic Radiology, Institute of Diagnostics, Oulu University Hospital, Medical Research Center, University of Oulu, Oulu, Finland.
authors.forename: Jaakko L
authors.initials: JL
authors.lastname: Niinimäki
authors.affiliation: Division of Orthopaedic and Trauma Surgery, Department of Surgery, Oulu University Hospital, Medical Research Center, University of Oulu, Oulu, Finland.
authors.forename: Tomi O P
authors.initials: TOP
authors.lastname: Nousiainen
authors.affiliation: Division of Orthopaedic and Trauma Surgery, Department of Surgery, Oulu University Hospital, Medical Research Center, University of Oulu, Oulu, Finland.
authors.forename: Juhana I
authors.initials: JI
authors.lastname: Leppilahti
mesh_terms: D000077:Acetabulum / Q000601:surgery*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects / Q000295:instrumentation*; D005260:Female; D006621:Hip Joint / Q000601:surgery; D006622:Hip Prosthesis / Q000009:adverse effects* / Q000706:statistics & numerical data; D006801:Humans; D008297:Male; D061825:Metal-on-Metal Joint Prostheses / Q000009:adverse effects* / Q000706:statistics & numerical data; D008875:Middle Aged; D016017:Odds Ratio; D012086:Reoperation / Q000706:statistics & numerical data*; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012306:Risk; D055815:Young Adult
keywords: Lewinnek's safe zone; acetabular component orientation; metal-on-metal; revision; total hip arthroplasty