title: The John Charnley Award: Diagnostic accuracy of MRI versus ultrasound for detecting pseudotumors in asymptomatic metal-on-metal THA.
abstract: BACKGROUND
  The prevalence of pseudotumors in patients with large-head metal-on-metal (MOM) THA has been the subject of implant recalls and warnings from various regulatory agencies. To date, there is no consensus on whether ultrasound or MRI is superior for the detection of pseudotumors.
  
  
  OBJECTIVE
  We prospectively compared ultrasound to MRI for pseudotumor detection in an asymptomatic cohort of patients with MOM THAs. We also compared ultrasound to MRI for assessment of pseudotumor growth and progressive soft tissue involvement at a 6-month interval.
  
  
  METHODS
  We enrolled 40 patients with large-head MOM THAs in the study. The mean age was 54 years (range, 34-76 years). The mean time from surgery was 54 months (range, 40-81 months). There were 28 men and 12 women. All patients underwent ultrasound and MRI using slice encoding for metal artifact correction. The gold standard was defined as follows: if both ultrasound and MRI agreed, this was interpreted as concordant and the result was considered accurate.
  
  
  RESULTS
  Ultrasound and MRI agreed in 37 of 40 patients (93%). The prevalence of pseudotumors was 31% (12 of 39) in our cohort. Twenty-three of 39 patients (59%) had completely normal tests and four (10%) had simple fluid collections. Ultrasound had a sensitivity of 100% and specificity of 96% while MRI had a sensitivity of 92% and specificity of 100%.
  
  
  CONCLUSIONS
  A negative ultrasound rules out pseudotumor in asymptomatic patients as this test is 100% sensitive. Given its lower cost, we recommend ultrasound as the initial screening tool for pseudotumors.
authors.affiliation: Division of Lower Limb Reconstruction and Oncology, Department of Orthopaedics, University of British Columbia, Room 3114, 910 West 10th Avenue, Vancouver, British Columbia, Canada, V5Z 4E3, garbuz@shaw.ca.
authors.forename: Donald S
authors.initials: DS
authors.lastname: Garbuz
authors.forename: Brian A
authors.initials: BA
authors.lastname: Hargreaves
authors.forename: Clive P
authors.initials: CP
authors.lastname: Duncan
authors.forename: Bassam A
authors.initials: BA
authors.lastname: Masri
authors.forename: David R
authors.initials: DR
authors.lastname: Wilson
authors.forename: Bruce B
authors.initials: BB
authors.lastname: Forster
mesh_terms: D000328:Adult; D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects* / Q000295:instrumentation*; D058070:Asymptomatic Diseases; D005260:Female; D006104:Granuloma, Plasma Cell / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000209:etiology / Q000473:pathology; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D006622:Hip Prosthesis; D006801:Humans; D066298:In Vitro Techniques; D008279:Magnetic Resonance Imaging; D008297:Male; D061825:Metal-on-Metal Joint Prostheses; D008875:Middle Aged; D011237:Predictive Value of Tests; D011446:Prospective Studies; D011474:Prosthesis Design; D015203:Reproducibility of Results; D013997:Time Factors; D016896:Treatment Outcome; D014463:Ultrasonography