title: Low-field-strength MR imaging of failed hip arthroplasty: association of femoral periprosthetic signal intensity with radiographic, surgical, and pathologic findings.
abstract: OBJECTIVE
  To investigate the association between periprosthetic signal intensity at low-field-strength magnetic resonance (MR) imaging after failed hip arthroplasty and radiographic, surgical, and pathologic findings.
  
  
  METHODS
  The study group comprised 22 consecutive women who underwent hip arthroplasty (mean age, 62 years; age range, 35-74 years). All patients underwent MR imaging prior to revision surgery. Coronal fast short inversion time inversion-recovery (STIR) images and spin-echo T1-weighted images were obtained with a 0.5-T MR imaging unit before and after administration of contrast material. The periprosthetic region was divided into the seven femoral Gruen zones. Two observers retrospectively analyzed signal intensity patterns. Association of signal intensity patterns with radiographic, surgical, and pathologic findings was determined with chi2 analysis and generalized estimating equations.
  
  
  RESULTS
  Diagnostic-quality images were obtained for 150 zones. Periprosthetic signal intensity was greater than that of bone marrow in the distal femur on the fast STIR images, and no contrast enhancement was seen on the T1-weighted images (type I signal intensity pattern) in 11 zones. Signal intensity was greater than that of bone marrow on the fast STIR images, and contrast enhancement was seen on the T1-weighted images (type II signal intensity pattern) in 45 zones. Signal intensity was less than or equal to that of bone marrow on the fast STIR images, and no contrast enhancement was seen on the T1-weighted images (type III signal intensity pattern) in 94 zones. Type I and II patterns were associated with focal or nonfocal lucency, an unstable stem, and fibrosis or granuloma. A type III pattern was associated with a normal radiographic appearance, a stable stem, and normal bone tissue. Significant association was demonstrated between periprosthetic signal intensity and radiographic (P <.001, chi2 test and generalized estimating equations), surgical (P <.05, Mantel-Haenszel chi2 test and generalized estimating equations), and pathologic findings (P <.05, chi2 test).
  
  
  CONCLUSIONS
  Low-field-strength MR imaging depicted periprosthetic tissue signal intensity that was significantly associated with radiographic, surgical, and pathologic findings.
authors.affiliation: Department of Radiology, Showa University Fujigaoka Hospital, Yokohama, Kanagawa, Japan. sugimoto@jichi.ac.jp
authors.forename: Hideharu
authors.initials: H
authors.lastname: Sugimoto
authors.forename: Isao
authors.initials: I
authors.lastname: Hirose
authors.forename: Etsuo
authors.initials: E
authors.lastname: Miyaoka
authors.forename: Akifumi
authors.initials: A
authors.lastname: Fujita
authors.forename: Yuko
authors.initials: Y
authors.lastname: Kinebuchi
authors.forename: Wakako
authors.initials: W
authors.lastname: Yamamoto
authors.forename: Yu-Ichi
authors.initials: Y
authors.lastname: Itoh
mesh_terms: D000328:Adult; D000368:Aged; D019644:Arthroplasty, Replacement, Hip; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging / Q000473:pathology* / Q000601:surgery; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008875:Middle Aged; D011475:Prosthesis Failure; D011859:Radiography; D012086:Reoperation