title: Are ceramic-on-ceramic bearings in total hip arthroplasty associated with reduced revision risk for late dislocation?
abstract: BACKGROUND
  Dislocation is a major complication after primary total hip arthroplasty (THA), but little is known about the potential relationships between bearing materials and risk of dislocation. Dislocation within the first year after surgery is typically related to either surgical error or patient inattention to precautions, but the reasons for dislocation after the first year are often unclear, and whether ceramic bearings are associated with an increased or decreased likelihood of late dislocation is controversial.
  
  
  OBJECTIVE
  The purpose of this study was to use a national registry to assess whether the choice of bearings-metal-on-polyethylene (MoP), ceramic-on-polyethylene (CoP), ceramic-on-ceramic (CoC), or metal-on-metal (MoM)-is associated with differences in the risk of late dislocation.
  
  
  METHODS
  Data from primary THAs were extracted from the New Zealand Joint Registry over a 10-year period. The mean age of patients was 69 years (SD ± 12 years), and 53% were women. The median followup in this population was 7 years (range, 1-13 years). The surgical approach used was posterior in 66% of THAs, lateral in 29%, and anterior in 5%. The primary endpoint was late revision for dislocation with "late" defined as greater than 1 year postoperatively. A total of 73,386 hips were available for analysis: 65% MoP, 17% CoP, 10% CoC, and 7% MoM. In general, patients receiving CoC and MoM bearings were younger compared with patients receiving CoP and MoP bearings.
  
  
  RESULTS
  Four percent of the hips were revised (3130 THAs); 867 THAs were revised for dislocation. Four hundred seventy THAs were revised for dislocation after the first postoperative year. After adjusting for head size, age, and surgical approach, only CoP (hazard ratio [HR], 2.10; p = 0.021) demonstrated a higher proportion of revision, whereas MoP did not (HR, 1.76; 95% p = 0.075). There were no differences of revisions for dislocation in the CoC (HR, 1.60; p = 0.092) and MoM cohorts (HR, 1.54; p = 0.081).
  
  
  CONCLUSIONS
  Dislocation is a common reason for revision after THA. The relationships between bearing materials and risk of revision for late dislocation remain controversial. This large registry study demonstrated that bearing surface had little association with the incidence of late dislocation. Future studies with longer followups should continue to investigate this question.
  
  
  METHODS
  Level III, therapeutic study.
authors.affiliation: Department of Orthopaedic Surgery, Middlemore Hospital, South Auckland Clinical School, University of Auckland, Otahuhu, 93311, Auckland, New Zealand. r.pitto@auckland.ac.nz.
authors.forename: Rocco P
authors.initials: RP
authors.lastname: Pitto
authors.affiliation: Department of Orthopaedic Surgery, Middlemore Hospital, South Auckland Clinical School, University of Auckland, Otahuhu, 93311, Auckland, New Zealand.
authors.forename: Mikaela
authors.initials: M
authors.lastname: Garland
authors.affiliation: Lariboisière/Saint-Louis Hospital, University of Paris Denis Diderot, Paris, France.
authors.forename: Laurent
authors.initials: L
authors.lastname: Sedel
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects* / Q000295:instrumentation*; D002516:Ceramics; D018572:Disease-Free Survival; D005260:Female; D006617:Hip Dislocation / Q000175:diagnosis / Q000453:epidemiology / Q000601:surgery*; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D006622:Hip Prosthesis; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D009520:New Zealand / Q000453:epidemiology; D011474:Prosthesis Design; D011475:Prosthesis Failure; D011859:Radiography; D012042:Registries; D012086:Reoperation; D012189:Retrospective Studies; D012307:Risk Factors; D013997:Time Factors; D016896:Treatment Outcome