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The reliability of four widely used patellar height ratios
Dennis van Duijvenbode1, Michel Stavenuiter2, Bart Burger2
1Department of Orthopaedic Surgery, Medisch Centrum Alkmaar/Centre for Orthopaedic Research Alkmaar (CORAL), Alkmaar, the Netherlands. d.c.duijvenbode@mca.nl.
Purpose:
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.
Conclusion:
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.
