title: Delayed dislocation following metal-on-polyethylene arthroplasty of the hip due to 'silent' trunnion corrosion.
abstract: OBJECTIVE
  We present a case series of ten metal-on-polyethylene total hip arthroplasties (MoP THAs) with delayed dislocation associated with unrecognised adverse local tissue reaction due to corrosion at the trunnion and pseudotumour formation.
  
  
  METHODS
  The diagnosis was not suspected in nine of the ten patients (six female/four male; mean age 66 years), despite treatment in a specialist unit (mean time from index surgery to revision was 58 months, 36 to 84). It was identified at revision surgery and subsequently confirmed by histological examination of resected tissue. Pre-operative assessment and culture results ruled out infection. A variety of treatment strategies were used, including resection of the pseudotumour and efforts to avoid recurrent dislocation.
  
  
  RESULTS
  The rate of complications was high and included three deep infections, two patients with recurrent dislocation, and one recurrent pseudotumour.
  
  
  CONCLUSIONS
  This series (mean follow-up of 76 months following index procedure and 19 months following revision THA) demonstrates that pseudotumour is an infrequent but important contributor to delayed instability following MoP THA. It is easy to overlook in the differential diagnosis, especially if the alignment of the components is less than optimal, leading to an assumption that malalignment is the cause of the dislocation. The instability is likely to be multifactorial and the revision surgery is complex.
  
  
  CONCLUSIONS
  Due to the high complication rate associated with revision in this cohort, the diagnosis should be borne in mind when counselling patients regarding the risks of revision surgery.
authors: University of British Columbia, 3rd Floor 910 West 10th Avenue, Vancouver, BC, V5Z 4E3, Canada.
authors: N J
authors: NJ
authors: Lash
authors: University of Bristol, Level 1 Learning and Research Building, Southmead Hospital, Bristol, BS10 5NB, UK.
authors: M R
authors: MR
authors: Whitehouse
authors: University of British Columbia, 3rd Floor 910 West 10th Avenue, Vancouver, BC, V5Z 4E3, Canada.
authors: N V
authors: NV
authors: Greidanus
authors: University of British Columbia, 3rd Floor 910 West 10th Avenue, Vancouver, BC, V5Z 4E3, Canada.
authors: D S
authors: DS
authors: Garbuz
authors: University of British Columbia, 3rd Floor 910 West 10th Avenue, Vancouver, BC, V5Z 4E3, Canada.
authors: B A
authors: BA
authors: Masri
authors: University of British Columbia, 3rd Floor 910 West 10th Avenue, Vancouver, BC, V5Z 4E3, Canada.
authors: C P
authors: CP
authors: Duncan
mesh_terms: D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects*; D003343:Corrosion; D005260:Female; D006104:Granuloma, Plasma Cell / Q000209:etiology; D006617:Hip Dislocation / Q000209:etiology*; D006622:Hip Prosthesis; D006801:Humans; D008297:Male; D008875:Middle Aged; D020959:Polyethylene / Q000009:adverse effects; D011300:Preoperative Care / Q000379:methods; D011475:Prosthesis Failure / Q000009:adverse effects*; D012008:Recurrence; D012086:Reoperation
chemical_list: D020959:Polyethylene
keywords: Total Hip Arthroplasty; Dislocation; Pseudotumour; Trunnion