Reproducibility test on a children's insole for measuring the dynamic plantar pressure distribution

INTRODUCTION:: This study aimed to establish the reproducibility of a insole measuring system specifically designed for use inside children's shoes. It is important to carry out such an investigation before any measurements are taken in order to ensure that any errors associated with the system are known and quantified. The children's insole had 84 pressure sensors, compared to the adult insoles, with 99 pressure sensors. The sensor technology was essentially the same as used in the adult Pedar system, and incorporated capacitance-based pressure transducers. MATERIALS AND METHOD:: An eight year old boy, height 123 cm, weight 29 kg, was used in the study. Dynamic tests were carried out with the Pedar insole measuring system. The subject walked on a treadmill, at a speed comfortable for him (3 km/h), with the insoles placed between the foot and the shoe. No fixation of the insole to the shoe was used. Seven runs were completed, each with four tests recorded of more than twenty steps. In between each run the insoles were completely removed from the shoe and then replaced. A zero measurement was also taken before the continuation of the next run. Before analysis of the data, twenty steps were selected. The first two steps in each sequence were ignored and the following twenty steps were used in the analysis, ten each for the left and the right foot. Any additional steps recorded were also ignored. The average force for the test data file was initially noted, together with the local pressure for each of the forefoot, midfoot, heel and toe regions, for both the left and the right foot, separately. RESULTS:: The within test data and in-between test data when walking on a treadmill at constant speed was found to be reproducible (F(0.01)) for 6 out of 7 tests for the left and the right foot. The standard deviation of the average force for the left and the right foot was 3%. The 95% confidence intervals for the mean of the peak pressure in the total object was within 6% for the treadmill and free walking data. There was no significant difference between these data. The 95% confidence intervals for the mean of the peak pressure under the big toe was 9% for the treadmill data and 16% for the free walking data. CONCLUSIONS:: These results, together with other published data (McPoil et al. 1995) show that the pedar children's insole system provides accurate and reproducible measurements of the dynamic plantar pressure distribution. The clinician can therefore use this system with confidence as a therapeutic or rehabilitative tool.