title: Computerized assessment of sagittal curvatures of the spine: comparison between Cobb and tangent circles techniques.
abstract: OBJECTIVE
  The tangent circles technique has been proposed as an alternative to the Cobb angle technique to assess sagittal curves of the spine. However, it has never been compared directly to the Cobb technique. This study compares the reproducibility and clinical relevance of the maximum Cobb angle and tangent circles techniques.
  
  
  METHODS
  Standing sagittal radiographs of the spine of 10 adolescents with idiopathic scoliosis, 10 adolescents with spondylolisthesis, and 10 healthy adolescents were used. Thoracic kyphosis (TK) and lumbar lordosis (LL) were measured by 3 observers using the maximum Cobb angle and the tangent circles techniques. Intra- and interobserver intraclass correlation coefficients (ICCs) were calculated.
  
  
  RESULTS
  Intra- and interobserver ICCs for TK were 0.88 and 0.85, respectively, for the maximum Cobb angle technique, and 0.94 and 0.83, respectively, for the tangent circles technique. Intra- and interobserver ICCs for LL were 0.97 and 0.77, respectively, for the maximum Cobb angle technique, and 0.88 and 0.94, respectively, for the tangent circles technique. The 2 techniques were highly correlated for the measurement of the TK (r=0.93) and LL (r=0.88).
  
  
  CONCLUSIONS
  Both techniques provide excellent intra- and interobserver reproducibility. Tangent circles technique may be a good alternative to the Cobb angle technique because it allows the evaluation of the global geometry of sagittal spinal curves, especially when there is limited visibility of bony structures on radiographs.
authors.affiliation: Faculty of Medicine, Université de Montréal, Montréal, Québec, Canada.
authors.forename: Fanny-Maud
authors.initials: FM
authors.lastname: Pinel-Giroux
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Mac-Thiong
authors.forename: Jacques A
authors.initials: JA
authors.lastname: de Guise
authors.forename: Eric
authors.initials: E
authors.lastname: Berthonnaud
authors.forename: Hubert
authors.initials: H
authors.lastname: Labelle
mesh_terms: D000293:Adolescent; D001837:Body Weights and Measures; D002648:Child; D005260:Female; D006801:Humans; D007738:Kyphosis / Q000000981:diagnostic imaging*; D008141:Lordosis / Q000000981:diagnostic imaging*; D008159:Lumbar Vertebrae; D008297:Male; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D013904:Thoracic Vertebrae