title: Multirater agreement for grading the femoral and tibial cartilage surface lesions at CT arthrography and analysis of causes of disagreement.
abstract: OBJECTIVE
  To assess the multirater agreement of the modified Outerbridge system for the grading of predefined areas of femorotibial cartilage at CT arthrography with multiple readers, with varying experience.
  
  
  METHODS
  Five readers with varying experience (two junior radiologists, three musculoskeletal radiologists including two experts in cartilage imaging) separately analyzed 962 cartilage sectors from pre-divided knee CT arthrograms with femorotibial osteoarthritis (Kellgren/Lawrence=3). Each cartilage area was graded twice by each reader, at a three-month interval, according to the modified 5-grade Outerbridge system. Interobserver and intraobserver agreement were assessed. After the second reading, 121 areas exhibiting the highest interobserver disagreement were reviewed in consensus to determine the sources of disagreement.
  
  
  RESULTS
  The global interobserver agreement was fair (k=0.35), and increased with the grade (from k=0.14 to k=0.76 from grade 0-4). The intraobserver agreement varied with the readers' experience from moderate (k=0.59) to almost perfect (k=0.92). The majority of cases of disagreement (44%) was due to difficulties in assessing the normal variations of cartilage thickness, including diffuse cartilage thinning (23%) and normal variants of cartilage thickness (22%). 32% of cases of disagreement were due to retrospectively avoidable interpretation errors.
  
  
  CONCLUSIONS
  The multirater agreement of the modified Outerbridge system is only fair when readers of different level of experience are taken into account, and interobserver agreement increases with readers' experience. However, interobserver agreement is substantial for grade 4 lesions. We report normal variations of cartilage thickness that may improve observer agreement in reporting cartilage lesions.
authors.affiliation: Department of Radiology, Cliniques Universitaires St Luc - UC Louvain, Hippocrate Avenue 10/2942, B-1200 Brussels, Belgium; Department of Diagnostic and Interventional Radiology, Lausanne University Hospital, Bugnon 46, CH-1011 Lausanne, Switzerland. Electronic address: patrick.omoumi@chuv.ch.
authors.forename: Patrick
authors.initials: P
authors.lastname: Omoumi
authors.affiliation: Department of Radiology, Cliniques Universitaires St Luc - UC Louvain, Hippocrate Avenue 10/2942, B-1200 Brussels, Belgium.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Michoux
authors.affiliation: Department of Radiology, Cliniques Universitaires St Luc - UC Louvain, Hippocrate Avenue 10/2942, B-1200 Brussels, Belgium.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Larbi
authors.affiliation: Department of Radiology, Cliniques Universitaires St Luc - UC Louvain, Hippocrate Avenue 10/2942, B-1200 Brussels, Belgium.
authors.forename: Laure
authors.initials: L
authors.lastname: Lacoste
authors.affiliation: Department of Radiology, Cliniques Universitaires St Luc - UC Louvain, Hippocrate Avenue 10/2942, B-1200 Brussels, Belgium.
authors.forename: Frédéric E
authors.initials: FE
authors.lastname: Lecouvet
authors.affiliation: Department of Radiology, Cliniques Universitaires St Luc - UC Louvain, Hippocrate Avenue 10/2942, B-1200 Brussels, Belgium.
authors.forename: Vasiliki
authors.initials: V
authors.lastname: Perlepe
authors.affiliation: Department of Radiology, Cliniques Universitaires St Luc - UC Louvain, Hippocrate Avenue 10/2942, B-1200 Brussels, Belgium.
authors.forename: Bruno C
authors.initials: BC
authors.lastname: Vande Berg
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001175:Arthrography / Q000379:methods*; D002358:Cartilage, Articular / Q000000981:diagnostic imaging* / Q000473:pathology*; D002983:Clinical Competence / Q000706:statistics & numerical data; D003287:Contrast Media; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging / Q000473:pathology; D006801:Humans; D007482:Iothalamate Meglumine; D007483:Iothalamic Acid; D007719:Knee Joint / Q000000981:diagnostic imaging* / Q000473:pathology*; D008297:Male; D008875:Middle Aged; D061330:Multidetector Computed Tomography / Q000379:methods*; D015588:Observer Variation; D010003:Osteoarthritis / Q000000981:diagnostic imaging*; D011856:Radiographic Image Enhancement; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012720:Severity of Illness Index; D013977:Tibia / Q000000981:diagnostic imaging / Q000473:pathology
chemical_list: D003287:Contrast Media; D007483:Iothalamic Acid; C001694:meglumine ioxithalamate; D007482:Iothalamate Meglumine
keywords: Arthrography; Cartilage; Computed tomography; Grading system; Osteoarthritis; Thickness