Intrarater and interrater reliability of the Eaton classification of basal joint arthritis.

The Eaton classification is a radiographic rating used to define the severity of basal joint arthritis. Despite widespread use, the intrarater and interrater reliability has never been determined. Seven men and 33 women, mean age 60 years (range, 31-88 y) were clinically diagnosed with basal joint arthritis. Forty radiographs of these patients' basal joints (21 right and 19 left) were staged according to Eaton, stages I through IV. Three hand surgeons with a Certificate of Added Qualification and 3 orthopedic surgical residents reviewed the films on 2 separate occasions at least 1 week apart. The results of intrarater and interrater reliability were assessed by using kappa statistical analysis, with results classified as poor (0-.50), moderate (.51-.75), or excellent (>.75). The overall mean intrarater and interrater reliability was moderate,.657 and.529, respectively. The hand surgeons' intrarater reliability (.666) was slightly better than the residents (.648). There was a greater difference in the mean interrater reliabilities among the hand surgeons (.601) than the orthopedic residents (.487). These results are similar to those found when other orthopedic radiographic classifications have been evaluated for interrater and intrarater reliability.