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There is no standardized method reported in the literature to measure ROM of the ankle after a total ankle arthroplasty, which limits the possibility to compare results from the various ankle designs. It seems that most of the measurements are a combination of ankle and midfoot motion, not the tibiotalar joint. A protocol was developed to accurately measure the true tibiotalar and midfoot motion before and after an ankle replacement. Lateral radiographs were taken of the ankle with the patient in a weightbearing position, and measurements were done along fixed landmarks. In this study, the tibiotalar, midfoot, and combined ROM were measured preoperative and 1 year postoperative in a standardized, reproducible fashion. The preoperative tibiotalar ROM was 18.5° and combined ankle and midfoot motion 25.1°. The true tibiotalar motion after an Agility total ankle arthroplasty was 23.4°, and the combined ankle and midfoot motion was 31.3°. The average improvement in ROM in the tibiotalar joint was approximately 5°, and combined ROM was 6.1°. Preoperative ROM proved to be the main factor determining the eventual postoperative ROM. It is possible to accurately measure the true ankle and the midfoot motion and those measurements should be used when reporting on the results of ankle replacements. Total ankle arthroplasty resulted in a statistically significant, but clinically less than expected, increase in ROM.