Analysis of agreement between the German translation of the American Foot and Ankle Society's Ankle and Hindfoot Scale (AOFAS-AHS) and the Foot Function Index in its validated German translation by Naal et al. (FFI-D)

Despite its wide use in clinical outcome measurement, there is yet no validated German language version of the AOFAS-AHS available. After finishing cross-cultural adaption of the AOFAS-AHS according to the AAOS guidelines, an analysis of agreement was carried out. This was done by means of the 18-item Foot Function Index in its validated German translation by Naal et al. (FFI-D). The results of 91 orthopedic patients as well as healthy persons in both scores were then compared intraindividually. The cohort consisted of 46 individuals with hindfoot disorders and 45 persons without any hindfoot complaints. The FFI-D-Score was linearly transformed in the range 0-100 points of the AOFAS. Encouraging correlation was then found for the patients with hindfoot disorders (Spearman's correlation 0.73 (95 % CI 0.52-0.85); a median deviation of -2 points (interquartile range -13 points; +13 points) in patients with hindfoot disorders implied good median intraindividual score concordance. However, with 30 of these 46 patients showing score deviations beyond or below a pre-specified +/- 10 points range of clinically tolerable deviations, the scores cannot be considered exchangeable. Although the agreement analysis was performed for the German translation of the two questionnaires, analogous results can be expected also for other languages. It should be noted that the results do not allow for judging which of the scores is better suited to give a valid statement on patient outcome in treatment of hindfoot disorders. To verify which of these two scores is better suited to represent hindfoot-dysfunction a subsequent study using instrumental gait analysis and surface EMG is being carried out.