title: Which imaging modality is most effective for identifying pseudotumours in metal-on-metal hip resurfacings requiring revision: ultrasound or MARS-MRI or both?
abstract: OBJECTIVE
  The aims of this study were to compare the diagnostic test characteristics of ultrasound alone, metal artefact reduction sequence MRI (MARS-MRI) alone, and ultrasound combined with MARS-MRI for identifying intra-operative pseudotumours in metal-on-metal hip resurfacing (MoMHR) patients undergoing revision surgery.
  
  
  METHODS
  This retrospective diagnostic accuracy study involved 39 patients (40 MoMHRs). The time between imaging modalities was a mean of 14.6 days (0 to 90), with imaging performed at a mean of 5.3 months (0.06 to 12) before revision. The prevalence of intra-operative pseudotumours was 82.5% (n = 33).
  
  
  RESULTS
  Agreement with the intra-operative findings was 82.5% (n = 33) for ultrasound alone, 87.5% (n = 35) for MARS-MRI alone, and 92.5% (n = 37) for ultrasound and MARS-MRI combined. The diagnostic characteristics for ultrasound alone and MARS-MRI alone reached similar sensitivities (90.9% vs 93.9%) and positive predictive values (PPVs; 88.2% vs 91.2%), but higher specificities (57.1% vs 42.9%) and negative predictive values (NPVs; 66.7% vs 50.0%) were achieved with MARS-MRI. Ultrasound and MARS-MRI combined produced 100% sensitivity and 100% NPV, whilst maintaining both specificity (57.1%) and PPV (91.7%). For the identification of a pseudotumour, which was confirmed at revision surgery, agreement was substantial for ultrasound and MARS-MRI combined (κ = 0.69), moderate for MARS-MRI alone (κ = 0.54), and fair for ultrasound alone (κ = 0.36).
  
  
  CONCLUSIONS
  These findings suggest that ultrasound and/or MARS-MRI have a role when assessing patients with a MoMHR, with the choice dependent on local financial constraints and the availability of ultrasound expertise. However in patients with a MoMHR who require revision, combined imaging was most effective.
  
  
  CONCLUSIONS
  Combined imaging with ultrasound and MARS-MRI always identified intra-operative pseudotumours if present. Furthermore, if neither imaging modality showed a pseudotumour, one was not found intra-operatively.
authors.affiliation: NDORMS and Nuffield Orthopaedic Centre, Oxford, UK.
authors.forename: G S
authors.initials: GS
authors.lastname: Matharu
authors.affiliation: NDORMS and Nuffield Orthopaedic Centre, Oxford, UK.
authors.forename: R
authors.initials: R
authors.lastname: Mansour
authors.affiliation: NDORMS and Nuffield Orthopaedic Centre, Oxford, UK.
authors.forename: O
authors.initials: O
authors.lastname: Dada
authors.affiliation: NDORMS and Nuffield Orthopaedic Centre, Oxford, UK.
authors.forename: S
authors.initials: S
authors.lastname: Ostlere
authors.affiliation: NDORMS and Nuffield Orthopaedic Centre, Oxford, UK.
authors.forename: H G
authors.initials: HG
authors.lastname: Pandit
authors.affiliation: NDORMS and Nuffield Orthopaedic Centre, Oxford, UK.
authors.forename: D W
authors.initials: DW
authors.lastname: Murray
mesh_terms: D000328:Adult; D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects*; D005260:Female; D006104:Granuloma, Plasma Cell / Q000175:diagnosis* / Q000000981:diagnostic imaging; D062785:Hemiarthroplasty / Q000009:adverse effects; D006622:Hip Prosthesis; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D061825:Metal-on-Metal Joint Prostheses / Q000009:adverse effects*; D008875:Middle Aged; D064847:Multimodal Imaging / Q000379:methods; D011446:Prospective Studies; D011475:Prosthesis Failure / Q000009:adverse effects; D012086:Reoperation; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D014463:Ultrasonography
keywords: Metal-on-metal; hip resurfacing; pseudotumour; MARS MRI; ultrasound; revision