A PEDOBAROGRAPHY-BASED TOOL FOR FUNCTIONAL ANALYSIS OF THE FOOT

In podiatric medicine, diagnosis of foot disorders is often merely based on tests of foot function in static conditions or on visual assessment of the patient9s gait. There is a lack of tools for the analysis of foot type and for diagnosis of foot ailments. In fact, static footprints obtained via carbon paper imprint material have traditionally been used to determine the foot type or highlight foot regions presenting excessive plantar pressure, and the data currently available to podiatrists and orthotists on foot function during dynamic activities, such as walking or running, are scarce. The device presented in this paper aims to improve current foot diagnosis by providing an objective evaluation of foot function based on pedobarographic parameters recorded during walking. 23 healthy subjects (16 female, 7 males; age 35 ± 15 years; weight 65.3 ± 12.7; height 165 ± 7 cm) with different foot types volunteered in the study. Subjects9 feet were visually inspected with a podoscope to assess the foot type. A tool, comprised of a 2304-sensor pressure plate (P-walk, BTS, Italy) and an ad-hoc software written in Matlab (The Mathworks, US), was used to estimate plantar foot morphology and functional parameters from plantar pressure data. Foot dimensions and arch-index, i.e. the ratio between midfoot and whole footprint area, were assessed against measurements obtained with a custom measurement rig and a laser-based foot scanner (iQube, Delcam, UK). The subjects were asked to walk along a 6m walkway instrumented with the pressure plate. In order to assess the tool capability to discriminate between the most typical walking patterns, each subject was asked to walk with the foot in forcibly pronated and supinated postures. Additionally, the pressure plate orientation was set to +15°, +30°, −15° and −30° with respect to the walkway main direction to assess the accuracy in measuring the foot progression angle (i.e. the angle between the foot axis and the direction of walk). At least 5 walking trials were recorded for each foot in each plate configuration and foot posture. The device allowed to estimate foot length with a maximum error of 5% and foot breadth with an error of 1%. As expected, the arch-index estimated by the device was the lowest in the cavus-feet group (0.12 ± 0.04) and the highest in the flat-feet group (0.29 ± 0.03). These values were between 4 – 10 % lower than the same measurements obtained with the foot scanner. The centre of pressure excursion index [1] was the lowest in the forcibly-pronated foot and the largest in the supinated foot. While the pressure plate used here has some limitations in terms of spatial resolution and sensor technology [2], the tool appears capable to provide information on foot morphology and foot function with satisfying accuracy. Patient9s instrumental examination takes only few minutes and the data can be used by podiatrists to improve the diagnosis of foot ailments, and by orthotists to design or recommend the best orthotics to treat the foot condition.