Reliability of a quantitative rating scale for assessment of horses with distal tarsal osteoarthritis

Various radiographic rating scales have been described for use in horses with distal tarsal osteoarthritis but little information is available on their reliability. The aim of this study was to develop a radiographic rating scale based on the results of an expert consultation process (the Delphi process), and to test the reliability of the radiographic rating scale. Seven radiographic features were identified as important indicators of distal tarsal osteoarthritis and these were then incorporated in the radiographic rating scale, which used a 100-mm-long visual analog scale. On two occasions nine equine veterinarians applied the radiographic rating scale, and a verbal descriptive rating scale, to three sets of tarsal radiographs, each comprising four standard radiographic views. Reliability was assessed using Bland-Altman plots and by calculating the 95% agreement limits. Analysis of variance (ANOVA) was used to identify significant interactions between the ratings of different assessors made from different views and at each assessment. Rating of distal tarsal osteoarthritis was different for the nine assessors. The most precise second ratings were between 16 mm higher and 18 mm lower than the first. Significant variables were "joint," "assessor," and "assessment" (univariable ANOVA); and "joint and assessor" and "assessor and assessment" (multivariable ANOVA). The radiographic rating scale developed for interpretation of distal tarsal osteoarthritis was less reliable than a verbal descriptive rating scale.