Intra- and interobserver repeatability of radiographic measurements in hallux surgery: improvement and validation of a method.

To test the hypothesis that the reproducibility of radiographic measurements of the first metatarsophalangeal angle and the intermetatarsal angle I-II can be increased by exact guidelines, we calculated the intra- and interobserver reliability of both methods. 4 independent observers (2 senior residents and 2 orthopedic trainees) evaluated 50 pre- and 50 postoperative plain dorsoplantar radiographs with their method of preference and then with Mitchell et al.'s method (1958). The mean intraobserver coefficient of repeatability for the metatarsophalangeal angle improved from 5.9 degrees to 4.2 degrees and for the intermetatarsal angle I-II, from 4.4 degrees to 2.8 degrees. The interobserver coefficient of repeatability improved from 6.5 degrees to 5.0 degrees for the metatarsophalangeal angle, and from 4.9 degrees to 3.6 degrees for the intermetatarsal angle I-II. This improvement in measurement accuracy was more marked for postoperative measurements, due to deformation of the metatarsal after the osteotomy which made it more difficult to find the longitudinal axis of the metatarsal. The improvements in the accuracy of measurements were also greater in the two inexperienced observers, since their measurements differed more when they had no exact guidelines for their drawings.