title: What Is the Natural History of Asymptomatic Pseudotumors in Metal-on-metal THAs at Mid-term Followup?
abstract: BACKGROUND
  The risk of early revision because of pseudotumors in patients who have undergone large-head metal-on-metal (MoM) total hip arthroplasty (THA) is well documented. However, the natural history of asymptomatic pseudotumors or of MoM articulations without pseudotumors is less well understood. The aim of our study was to investigate the natural history of primary MoM THA at mid-term followup.
  
  
  OBJECTIVE
  The purposes of this study were: (1) Did previously detected pseudotumors persist or worsen in asymptomatic patients at mid-term followup; and if so, did any of them require revision THA? (2) Did new pseudotumors form in asymptomatic patients at mid-term followup? (3) What happened to serum trace metal ions at mid-term followup? (4) Were postoperative patient-reported outcome measures (PROMs) maintained at mid-term followup?
  
  
  METHODS
  Seventy-one patients who underwent a MoM THA using a Metasul LDH implant with a Durom acetabular cup and an M/L Taper stem between September 2005 and October 2008 were reviewed. All patients for this study were part of two previously published studies from our early followup. Data from the previous studies were used for comparison only. Two of the 71 patients (2.8%) were lost to followup. The mean age at operation was 56 years (range, 34-68 years). There were 24 female patients. All patients had serum trace metal ions testing, ultrasound imaging, and PROMs at a mean 3.5 years (early followup) after the index operation (range, 3-5 years) and delayed followup at a mean 7 years (range, 6.5-9 years). The indication to undertake revision THA was based on clinical evaluation and not solely on the investigation results.
  
  
  RESULTS
  Twenty-three of 71 patients (32%) had a positive ultrasound scan for pseudotumor at early followup. Of these, eight patients underwent revision THA (11% of MoM THA or 35% of patients with an early positive ultrasound scan). The mean time between positive ultrasound scan and revision surgery was 13 months (range, 5-22 months). Of the remaining 15 patients with pseudotumor noted on early ultrasound, 12 had persistent pseudotumor, two resolved, and one was lost to followup. Six patients (13%) with a normal ultrasound scan at early followup showed new ultrasound findings at delayed followup. Of these, four (8%) were conclusively diagnosed as pseudotumor and one was revised. Serum trace metal ion increased at mid-term followup in the seven cases that showed an increase in volume of pseudotumor. Of the five patients in whom the volume of pseudotumor decreased on ultrasound at mid-term followup, three showed a decrease in serum trace ions levels, whereas two showed an increase. New-onset pseudotumors at mid-term followup was associated with an increase in serum trace metal ions at mid-term followup only in two of six cases. PROMs at mid-term followup of patients in this study remain high.
  
  
  CONCLUSIONS
  At mid-term followup, approximately 35% of patients who develop an early pseudotumor undergo revision arthroplasty, whereas the remaining are asymptomatic. The incidence of new-onset ultrasound findings suggestive of pseudotumors at mid- to long-term followup is approximately 8% and these require continued surveillance.
  
  
  METHODS
  Level II, prognostic study.
authors.affiliation: Department of Orthopaedics, Vancouver General Hospital, University of British Columbia, JP North 3rd Floor, Room 3114, 910 West 10th Avenue, Vancouver, BC, V5Z 4E3, Canada. sujithkonan@yahoo.co.uk.
authors.forename: Sujith
authors.initials: S
authors.lastname: Konan
authors.affiliation: Department of Orthopaedics, Vancouver General Hospital, University of British Columbia, JP North 3rd Floor, Room 3114, 910 West 10th Avenue, Vancouver, BC, V5Z 4E3, Canada.
authors.forename: Clive P
authors.initials: CP
authors.lastname: Duncan
authors.affiliation: Department of Orthopaedics, Vancouver General Hospital, University of British Columbia, JP North 3rd Floor, Room 3114, 910 West 10th Avenue, Vancouver, BC, V5Z 4E3, Canada.
authors.forename: Bassam S
authors.initials: BS
authors.lastname: Masri
authors.affiliation: Department of Orthopaedics, Vancouver General Hospital, University of British Columbia, JP North 3rd Floor, Room 3114, 910 West 10th Avenue, Vancouver, BC, V5Z 4E3, Canada.
authors.forename: Donald S
authors.initials: DS
authors.lastname: Garbuz
mesh_terms: D000328:Adult; D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects*; D018450:Disease Progression; D005260:Female; D006104:Granuloma, Plasma Cell / Q000209:etiology* / Q000473:pathology; D006622:Hip Prosthesis / Q000009:adverse effects*; D006801:Humans; D007592:Joint Diseases / Q000209:etiology* / Q000473:pathology; D008297:Male; D061825:Metal-on-Metal Joint Prostheses / Q000009:adverse effects*; D008875:Middle Aged; D011474:Prosthesis Design; D012086:Reoperation; D012307:Risk Factors; D016896:Treatment Outcome