title: The reliability of four widely used patellar height ratios.
abstract: OBJECTIVE
  The objective of this study was to evaluate the inter-observer reliability and the intra-observer reliability of four patellar height ratios: Insall-Salvati (IS), modified Insall-Salvati (MIS), Blackburne-Peel (BP) and Caton-Deschamps (CD).
  
  
  METHODS
  The patellar height ratios were assessed by four independent examiners using weight-bearing lateral knee radiographs in 30° flexion. Intra-class correlation coefficients and Fleiss' kappa's were determined.
  
  
  RESULTS
  The inter-observer reliability was excellent for the IS and moderate for the other ratios. When the ratio values were categorized, the inter-observer reliability was strong for the IS, moderate for the MIS and BP, and poor for the CD. The intra-observer reliability was excellent for the IS, MIS and CD, and strong for the BP. When the ratio values were categorized, the intra-observer reliability was strong for the IS and MIS, and moderate for the other ratios.
  
  
  CONCLUSIONS
  Although the IS showed best reliability, we advise to use the MIS as it showed the second best reliability but is, according to the literature, associated with better validity.
authors.affiliation: Department of Orthopaedic Surgery, Medisch Centrum Alkmaar/Centre for Orthopaedic Research Alkmaar (CORAL), Alkmaar, the Netherlands. d.c.duijvenbode@mca.nl.
authors.forename: Dennis
authors.initials: D
authors.lastname: van Duijvenbode
authors.affiliation: Department of Orthopaedic Surgery, Medisch Centrum Alkmaar/Centre for Orthopaedic Research Alkmaar (CORAL), Alkmaar, the Netherlands.
authors.forename: Michel
authors.initials: M
authors.lastname: Stavenuiter
authors.affiliation: Department of Orthopaedic Surgery, Medisch Centrum Alkmaar/Centre for Orthopaedic Research Alkmaar (CORAL), Alkmaar, the Netherlands.
authors.forename: Bart
authors.initials: B
authors.lastname: Burger
authors.affiliation: Department of Radiology, Medisch Centrum Alkmaar, Alkmaar, the Netherlands.
authors.forename: Cees
authors.initials: C
authors.lastname: van Dijke
authors.affiliation: Department of Radiology, Ziekenhuis Gelderse Vallei, Ede, the Netherlands.
authors.forename: Jacco
authors.initials: J
authors.lastname: Spermon
authors.affiliation: Faculty of Human Movement Sciences, MOVE Research Institute Amsterdam, Amsterdam, Netherlands.
authors.forename: Marco
authors.initials: M
authors.lastname: Hoozemans
mesh_terms: D000293:Adolescent; D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D015588:Observer Variation; D010329:Patella / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D011859:Radiography; D016059:Range of Motion, Articular; D015203:Reproducibility of Results; D012189:Retrospective Studies; D016474:Weight-Bearing; D055815:Young Adult
keywords: Patella alta; Patellar height; Reliability; Reproducibility; Variability