Reliability of in-shoe plantar pressure measurements in rheumatoid arthritis patients.

Plantar pressures measurement is a frequently used method in rehabilitation and related research. Metric characteristics of the F-Scan system have been assessed from different standpoints and in different patients, but not its reliability in rheumatoid arthritis patients. Therefore, our objective was to assess reliability of the F-Scan plantar pressure measurement system in rheumatoid arthritis patients. Twelve rheumatoid arthritis patients were included in this study. Plantar pressures measurement was carried out in six consecutive walks and average peak pressure on seven spots analyzed for each walk. Intraclass correlation was estimated for each spot and for within-patient coefficient of variation between spots. For each spot, average within-patient coefficient of variation between walks was also calculated. Repeated measures of analysis of variance and Hotelling's T test, both with Holm correction, were used to test equality of mean measurement across patients between walks. The intraclass correlations, which were all statistically significant at P<0.0001, ranged from 0.897 to 0.999, with a mean of 0.97 for single measure and 0.99 for average measure estimates. Overall median of within-patient coefficient of variation between walks was 7%. None of the tests of equality of means showed significant differences between walks. On both feet, the highest variability of measurements was observed at midfoot, whereas all the other spots demonstrated excellent reliability. The measurement setup was found to be highly reliable and therefore suitable for clinical practice, as well as for research. If possible, taking an average of several measurements is recommended.