Human gait on an irregular surface: Effects of age and peripheral neuropathy on step variability.

Abstract

Patients with peripheral neuropathy (PN), who are at a 6-fold risk for falls and 15 times more likely to be injured in a fall, find irregular surfaces particularly challenging to walk across. We therefore tested the hypothesis that neither age nor neuropathy would affect step variability during locomotion on flat or irregular surfaces. Step kinematics were measured optoelectronically while groups of healthy young (N = 12 women), older (N = 12 women) and older PN (N = 42, 20 women) subjects walked at their comfortable speed along a 6-m walkway covered with a flat or an irregular surface. The irregular surface increased step width and step time variability in all subject groups (p < 0.05): older women exhibited greater step width variability than younger women (15%, p < 0.001); PN patients exhibited similar step variability to the older women, but walked at a significantly slower speed (39%, p < 0.001) and with a wider base of support. Walking with a cane, running a finger along a vertical wall, or wearing bilateral semi-rigid ankle braces significantly reduced step variability in the PN patients (p < 0.05). When healthy young women (N = 12) walked across a flat surface, a single 1.2 cm-high protuberance under the medial forefoot caused crossover steps and stance foot inversional angular peak acceleration to correlate negatively with next-step step width (r = -0.4, p = 0.001). A 3-D direct dynamics biomechanical simulation predicted that foot inversional acceleration should be larger in older women, and larger still in PN patients due to decreased ankle torque development and rotational stiffness, and increased feedback delays. A similar 2-D frontal plane model for healthy young women demonstrated that a crossover step is likely due to an active response to the perturbation in the form of increased swing limb hip adduction torque. A crossover step is thus a strategy to rapidly unload the inverting stance foot. In conclusion, step time variability on the irregular surface differentiated these subject groups better than did corresponding tests on the flat surface. Step width variability increased in all groups on the irregular surface, particularly in the PN group. Finally, bilateral ankle braces improved the performance of neuropathic patients walking on the irregular surface.