title: The intra- and inter-observer reliability of the CT-scan based X index to quantify glenoid bone loss in chronic anterior shoulder instability and its impact on decision making.
abstract: OBJECTIVE
  The X index is a measure of the antero-inferior glenoid bone loss on unilateral 2D CT-scans in the preoperative analysis of chronic anterior shoulder instability. Recurrence rate was shown to be higher after stabilization surgery if X index is superior or equal to 0.4. The objective of this study was to assess the intra- and inter-observer reliability of the X index.
  
  
  METHODS
  Sixty patients with an X index ≥0.4 were included retrospectively. The X index was measured twice by two independent evaluators, 15 days apart. The measurement was performed on a unilateral 2D CT-scan by dividing the length of the antero-inferior glenoid defect over the maximal antero-posterior diameter of the glenoid. Reliability of X index was assessed with intra-class correlation coefficient (ICC, ρ). Two points were added to the ISIS calculation if its glenoid criterion was "zero" and we compared this modified score to the original one.
  
  
  RESULTS
  The intra-observer reliability of the X index measurement was "excellent" (ρ = 0.95 ± 0.01, p < 0.0001) while the inter-observer reliability was "good" (ρ = 0.59 ± 0.08, p < 0.0001). In patients with a glenoid bone loss visualized by the X index, 48.3 % had a negative sclerotic glenoid line sign. This proportion significantly decreased with the augmentation of the X index, p = 0.02. The average original ISIS score was 3.4 ± 1.9 and became 4.3 ± 1.7 (p < 0.00001) when the X index was incorporated.
  
  
  CONCLUSIONS
  The X index is a reliable and simple unilateral 2D CT-scan measurement. AP shoulder radiographs significantly underestimated glenoid bony lesions.
authors.affiliation: Hôpital Centre de Chirurgie Orthopédie et de la Main, 10 av Achille Baumann, 67400, Illkirch-Graffenstaden, France, ali.maqdes@gmail.com.
authors.forename: Ali
authors.initials: A
authors.lastname: Maqdes
authors.forename: Yves
authors.initials: Y
authors.lastname: Chammai
authors.forename: Regis
authors.initials: R
authors.lastname: Lengert
authors.forename: Shahnaz
authors.initials: S
authors.lastname: Klouche
authors.forename: Philippe
authors.initials: P
authors.lastname: Clavert
authors.forename: Philippe
authors.initials: P
authors.lastname: Hardy
authors.forename: Jean-Francois
authors.initials: JF
authors.lastname: Kempf
mesh_terms: D000293:Adolescent; D000328:Adult; D001862:Bone Resorption / Q000000981:diagnostic imaging*; D002908:Chronic Disease; D003657:Decision Making; D005260:Female; D061165:Glenoid Cavity / Q000000981:diagnostic imaging*; D006801:Humans; D007593:Joint Instability / Q000000981:diagnostic imaging* / Q000503:physiopathology; D008297:Male; D015588:Observer Variation; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods / Q000592:standards; D055815:Young Adult