Pressure distribution beneath the foot in sideslope walking
Dynamic loading profiles beneath the human foot during sideslope walking were determined and differences to level walking established. The contact area of the foot was measured, and the arch index derived from the footprint. Thirty healthy adults walked on a tillable walkway which had a polymer sensor pressure platform mounted at the mid-point. The sideways tilt could be adjusted in 2° increments from level to 8°. By walking in both directions on the sideslope, volunteers placed their right foot in either the upslope or downslope position. Loading profiles and contact areas were recorded for upslope and downslope foot placements at each angle of tilt. The characteristics of the electrically resistive polymer sensors were determined prior to the walking trials. The sensor output was non-linear, mean within-sensor variation =3% (maximum 8%), mean hysteresis -9% (maximum 13%), pressure threshold sensitivity =35 kPa, and mean between-sensor variation =8% (maximum 18%) over the surface of the platform. The dynamic behaviour was reliable to 26Hz. The sensor was found to be sensitive to shear. The impact of this characteristic was assessed by comparison with a similar platform incorporating capacitive transducers that were not shear sensitive. The polymer sensor system indicated increased pressures beneath the heel with upslope foot placement, and similar increases beneath the central metatarsals with downslope placement. These features were not apparent in the profiles returned by the second platform. For both platforms, however, the first metatarsal showed increased pressures with downslope placement but decreased pressures with upslope placement. In addition, the initial contact time and duration of loading for the first metatarsal altered significantly. The contact area of the foot changed systematically with sideslope walking, such that the arch index increased with upslope placement and decreased with downslope placement. This study demonstrated that the conventional approach of assessing level walking would fail to identify the increased foot pressures that occur on sideslopes. This may have crucial implications for ulceration risk assessment. The systematic changes in arch index and first metatarsal loading indicate that sideslope walking might be beneficial in revealing aspects of the mechanical behaviour of the human foot if combined with a simultaneous kinematic analysis. Potentially, the method offers a new approach to assessing the functional capacity of the foot for both clinical and research purposes.