title: Recurrence of dislocation following total hip arthroplasty revision using dual mobility cups was rare in 180 hips followed over 7 years.
abstract: BACKGROUND
  Dual mobility (DM) cups of mobile polyethylene were introduced to prevent total hip arthroplasty (THA) dislocation, but no large series with this design to treat recurrent instability have been reported.
  
  
  OBJECTIVE
  Our retrospective investigation ascertained the efficiency of DM cups in correction of recurrent dislocation and assessed any adverse effects.
  
  
  METHODS
  One hundred eighty THAs with recurrent instability were revised to DM cups in 180 patients (mean age, 67.4 ± 11.7 years; range, 19 to 92 years). Thirty-one patients (17.2%) underwent at least one earlier THA revision, and 15 (10.3%) incurred non-union of the greater trochanter. Of the initial group in 2009, 145 patients had completed evaluations which included assessment of the Harris Hip Score and a radiographic assessment at a mean follow-up of 7.7 ± 2.2 years (range, 4 to 14 years). The rate of survival was calculated considering any reason for revision as failure.
  
  
  RESULTS
  At follow-up, Harris hip score was 83.9 ± 16.1 (range, 21 to 100). Dislocation of the large articulation occurred in seven hips (4.8%), and only two recurred (1.4%) (one requiring additional revision). In addition, two intra-prosthetic dislocations of the small articulation (1.4%) were observed and needed revision surgery. The large number of earlier surgeries and non-union of the greater trochanter were related to recurrent instability. Two cups (1.4%) showed signs of definite loosening; six (4.1%) presented signs of possible loosening. Twenty-nine hips manifested femoral or acetabular osteolysis (20%), but only three were severe. Eight-year survival rate considering revision for any reason was 92.6% (95% CI, 85.5-96.4%).
  
  
  CONCLUSIONS
  This series indicates that DM cups are a viable option to treat recurrent THA instability. Their design provides a low risk of recurrent instability without increasing mechanical complications.
authors.affiliation: Orthopaedics Department, University of Amiens, place Victor-Pauchet, 80054 Amiens, France.
authors.forename: Patrice
authors.initials: P
authors.lastname: Mertl
authors.forename: Antoine
authors.initials: A
authors.lastname: Combes
authors.forename: Frédérique
authors.initials: F
authors.lastname: Leiber-Wackenheim
authors.forename: Michel Henri
authors.initials: MH
authors.lastname: Fessy
authors.forename: Julien
authors.initials: J
authors.lastname: Girard
authors.forename: Henri
authors.initials: H
authors.lastname: Migaud
keywords: bearing; dual mobility; hip arthroplasty; instability; polyethylene; revision; wear