The accuracy of footprint contact area measurements: Relevance to the design and performance of pressure platforms

Background: Footprints can be used for a variety of purposes, including the classification of foot type according to arch index. Pressure platforms offer an efficient method for collecting footprints but the accuracy of the electronic images, and their similarity to traditional ink prints, has not be determined. Objective: To determine the accuracy of contact area measurements estimated from multisensor, array type pressure platforms with a sensor element size of 5 × 6 mm. Design: Measurements of the contact areas of footprints were acquired directly from ink images and compared with estimates obtained using the grid pattern of an imitation sensor array. The difference between paired values was used as an indication of the likely measurement error. Results: Using a standard method, the imitation sensor array produced large errors (>10%) in the contact area measurements for all sites of the foot. By using a modified method, however, estimates for the main part of the footprint image and the hallux could be obtained to within almost 2% of the reference measurement. Contact area for the lesser toes was poorly estimated by the array, and the error always exceeded 8%. Conclusions: Operational pressure platforms have the potential to produce images with sufficient accuracy for use in many studies requiring footprint analysis. Measurements from the lesser toes should be interpreted with caution because of the large errors. New platforms, incorporating smaller sensors, would be valuable for future studies of the lesser toe region. Operational pressure systems should be evaluated individually to determine their specific error levels.