The Biomechanical Effects of Off-the-Shelf Foot Orthoses on the Gait of Able-Bodied Subjects: A Prospective Study.

Non-prescription foot orthoses (FO) or inner-soles can be obtained "off the shelf' from, for example, sports shops and chemists. They are available with different designs and materials, and are aimed at people who seek comfort and support for their feet. These FO can be found with similar components as prescription FO, however, the former are mass produced and therefore may not provide an appropriate fit for a particular subject's foot morphology. There is therefore a need to assess the biomechanical effects of these FO to determine their immediate effects and to suggest implications following long term use. Two "off the shelf' FO were investigated. One was a flat insole with a heel pad, the other a flat insole with a heel pad and a medial arch support. Level walking kinetic and kinematic data were collected before, during and after use of the FO from 12 healthy subjects (6 subjects per FO). A questionnaire was also developed to investigate the subject's perception of comfort and satisfaction with the FO. Healthy subjects were selected for the FO testing because these FO are intended for healthy subjects. The analysis was performed on a case by case basis such that each subject acted as his own reference. Prior to the FO study, a comparison of two available kinematic marker sets, the Skin Marker set (SMS), and the Wand Marker set (WMS), was undertaken to select the one with best performance to use in the gait measurements. Using the selected WMS a data repeatability study was subsequently carried out with 6 healthy subjects. The results from this study were used to detect changes in gait parameters due to FO use. The FO study showed that the orthoses used do not make a proper fit with all anatomical medial-longitudinal arches, may not reduce eversion in all users, and can cause an increased knee abduction moment, which may pose a potential health risk to the knee and surrounding structures. The results suggest that greater guidance needs to be provided with "off the shelf' orthoses, which may necessitate a more detailed clinical and biomechanical examination of the foot before purchase, and improved classification in terms of the components and materials used, and the dimensions of such orthoses