Frontal plane dynamic margins of stability in individuals with and without transtibial amputation walking on a loose rock surface.

Uneven walking surfaces pose challenges to balance, especially in individuals with lower extremity amputation. The purpose of this study was to determine if lateral stability of persons with unilateral transtibial amputation (TTA) is compromised when walking on a loose rock surface. Thirteen TTA and 15 healthy controls walked over level ground and over a loose rock surface at four controlled speeds. Dependent measures, including medial-lateral center of mass (COM) motion, step width variability, lateral arm swing velocity, and mean and variability of the minimum margins of stability (MOSmin), were compared between subject groups and across conditions. TTA had greater average MOSmin than Control subjects (p=0.018). TTA exhibited decreased MOSmin on their prosthetic limbs compared to their intact limbs (p=0.036), while Control subjects did not exhibit side to side differences. Both groups increased MOSmin with increasing walking speed (p≤0.001). There was no difference in the average MOSmin between walking surfaces (p=0.724). However, the variability of MOSmin was greater on the rocks compared to level ground. Both subject groups increased step width, step width variability, COM range of motion and peak COM velocity when walking on the rock surface. TTA exhibited greater variability of both step width and MOSmin, which suggests that they made larger step-to-step corrective responses, more often, to achieve the same average result.