title: Freedom Constrained Liner for the Treatment and Prevention of Dislocation in Total Hip Arthroplasty.
abstract: OBJECTIVE
  Dislocation is one of the most common complications following total hip arthroplasty. The aim of our study was to assess failure rate of the Biomet Freedom constrained liner (Biomet, Warsaw, IN, USA) either in revision surgery for recurrent dislocation, or as a preventive method in high dislocation risk patients.
  
  
  METHODS
  We assessed retrospectively 105 consecutive surgical procedures in 103 patients where a Freedom constrained liner or cup was used in Turku University Hospital over a 7-year period from 2007 to 2014. The mechanical failure rate of the device was assessed based on medical records. The average age of the patients was 73.4 years. The number of male patients was 53 (51%). Mean follow-up time was 2.5 years. The association between failure of the device and potential risk factors-age, gender, indication, and approach-was analyzed with logistic regression. Results were expressed by odd ratios and 95% confidence intervals.
  
  
  RESULTS
  The mechanical failure rate of the Freedom device was 6 out of 105 (5.7%). None of the 11 preventive primary THAs against dislocation failed, 4 out of 52 (7.7%) preventive revision THAs against dislocation failed, and 2 out of 42 (4.8%) of the treated dislocation cases failed. Four out of six failures were dislocations due to impingement and failure of the locking mechanism. Two liners failed because of loosening. The risk factors assessed were not associated with failure of the device.
  
  
  CONCLUSIONS
  We found out that the mechanical failure rate of a Freedom constrained device was low. These results encourage us to continue using the device.
authors.affiliation: 1 Department of Orthopaedics and Traumatology, Turku University Hospital, Turku, Finland.
authors.forename: M
authors.initials: M
authors.lastname: Karvonen
authors.affiliation: 1 Department of Orthopaedics and Traumatology, Turku University Hospital, Turku, Finland.
authors.forename: H
authors.initials: H
authors.lastname: Karvonen
authors.affiliation: 1 Department of Orthopaedics and Traumatology, Turku University Hospital, Turku, Finland.
authors.forename: M
authors.initials: M
authors.lastname: Seppänen
authors.affiliation: 2 Department of Anesthesiology, Turku University Hospital, Turku, Finland.
authors.forename: A
authors.initials: A
authors.lastname: Liukas
authors.affiliation: 3 Faculty of Science, University of Turku, Turku, Finland.
authors.forename: M
authors.initials: M
authors.lastname: Koivisto
authors.affiliation: 1 Department of Orthopaedics and Traumatology, Turku University Hospital, Turku, Finland.
authors.forename: K T
authors.initials: KT
authors.lastname: Mäkelä
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects* / Q000379:methods; D015331:Cohort Studies; D016001:Confidence Intervals; D005260:Female; D005500:Follow-Up Studies; D006617:Hip Dislocation / Q000209:etiology / Q000517:prevention & control* / Q000601:surgery*; D006622:Hip Prosthesis; D006801:Humans; D008297:Male; D016017:Odds Ratio; D011474:Prosthesis Design; D011475:Prosthesis Failure; D020127:Recovery of Function; D012086:Reoperation / Q000379:methods; D012189:Retrospective Studies; D018570:Risk Assessment; D016896:Treatment Outcome
keywords: Constrained liner; THA dislocation; complications after THA; freedom constrained liner; recurrent dislocation