To assess the reliability of the Eaton and Glickel classification for base of thumb osteoarthritis.
The interrater and intrarater reliability of this classification were assessed by comparing ratings from 6 raters using quadratic weighted kappa scores.
Median inter-rater reliability ranged from kappa of .53 to .54; intrarater reliability ranged from kappa of .60 to .82. Using unweighted kappa interrater reliability was "slightly" reliable, and intrarater reliability was "fairly" reliable. Overall, the value of the intraclass correlation for all 6 raters was .56.
This radiological classification does not describe all stages of carpometacarpal joint osteoarthritis accurately enough to permit reliable and consistent communication between clinicians. Therefore we believe it should be used with an understanding of its limitations when communicating disease severity between clinicians or as a tool to assist in clinical decision making.