title: Differentiation between grade 3 and grade 4 articular cartilage defects of the knee: fat-suppressed proton density-weighted versus fat-suppressed three-dimensional gradient-echo MRI.
abstract: BACKGROUND
  Fat-suppressed (FS) proton density (PD)-weighted magnetic resonance imaging (MRI) and FS three-dimensional (3D) gradient-echo imaging such as spoiled gradient-recalled (SPGR) sequence have been established as accurate methods for detecting articular cartilage defects.
  
  
  OBJECTIVE
  To retrospectively compare the diagnostic efficacy between FS PD-weighted and FS 3D gradient-echo MRI for differentiating between grade 3 and grade 4 cartilage defects of the knee with arthroscopy as the standard of reference.
  
  
  METHODS
  Twenty-one patients who had grade 3 or 4 cartilage defects in medial femoral condyle at arthroscopy and knee MRI were included in this study: grade 3, >50% cartilage defects; grade 4, full thickness cartilage defects exposed to the bone. Sagittal FS PD-weighted MR images and FS 3D gradient-echo images with 1.5 T MR images were independently graded for the cartilage abnormalities of medial femoral condyle by two musculoskeletal radiologists. Statistical analysis was performed by Fisher's exact test. Inter-observer agreement in grading of cartilage was assessed using kappa coefficients.
  
  
  RESULTS
  Arthroscopy revealed grade 3 defects in 17 patients and grade 4 defects in 4 patients in medial femoral condyles. For FS 3D gradient-echo images grade 3 defects were graded as grade 3 (n=15) and grade 4 (n=2), and all grade 4 defects (n=4) were correctly graded. However, for FS PD-weighted MR images all grade 3 defects were misinterpreted as grade 1 (n=1) and grade 4 (n=16), whereas all grade 4 defects (n=4) were correctly graded. FS 3D gradient-echo MRI could differentiate grade 3 from grade 4 defects (P=0.003), whereas FS PD-weighted imaging could not (P=1.0). Inter-observer agreement was substantial (kappa=0.70) for grading of cartilage using FS PD-weighted imaging, whereas it was moderate (kappa=0.46) using FS 3D gradient-echo imaging.
  
  
  CONCLUSIONS
  FS 3D gradient-echo MRI is more helpful for differentiating between grade 3 and grade 4 cartilage defects than is FS PD-weighted imaging.
authors.affiliation: Department of Radiology, Seoul St Mary's Hospital, Catholic University of Korea, Seoul, Korea.
authors.forename: So Yeon
authors.initials: SY
authors.lastname: Lee
authors.forename: Won-Hee
authors.initials: WH
authors.lastname: Jee
authors.forename: Sun Ki
authors.initials: SK
authors.lastname: Kim
authors.forename: In-Jun
authors.initials: IJ
authors.lastname: Koh
authors.forename: Jung-Man
authors.initials: JM
authors.lastname: Kim
mesh_terms: D000368:Aged; D001182:Arthroscopy; D002357:Cartilage Diseases / Q000175:diagnosis*; D002358:Cartilage, Articular / Q000473:pathology*; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D007719:Knee Joint / Q000473:pathology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies