Inter- and intraclass correlations for three standard foot radiographic measurements for plantar surface angles. Which measure is most reliable?

Abstract

BackgroundThe purpose of this study was to evaluate the reliability and reproducibility of three commonly used radiographic measures for plantar surface angles. MethodsThe calcaneal angle (CA), calcaneal pitch angle (CPA), and length-height index (LHI) was measured by three independent examiners on two occasions on lateral foot radiographs. Intra- and inter-rater correlations were calculated using a general linear estimate model and post-hoc tests for repeated measures. Bland–Altman’s plots with limits of agreement were used for observer differences in scores. ResultsThe intra-class correlations for the CA ranged from 0.91 to 0.94, for the CPA from 0.93 to 0.98, and for the LHI from 0.96 to 0.97. The inter-class correlations were 0.80 for CA, 0.83 for CPA and 0.93 for LHI. ConclusionsThe results of this study strongly suggest that the length-height index was the most consistent and reliable measure for arch height.Level of evidence: Diagnostic Level II, validity.