Mediolateral angular momentum changes in persons with amputation during perturbed walking

Abstract

Over 50% of individuals with lower limb amputation fall at least once each year. These individuals also exhibit reduced ability to effectively respond to challenges to frontal plane stability. The range of whole body angular momentum has been correlated with stability and fall risk. This study determined how lateral walking surface perturbations affected the regulation of whole body and individual leg angular momentum in able-bodied controls and individuals with unilateral transtibial amputation. Participants walked at fixed speed in a Computer Assisted Rehabilitation Environment with no perturbations and continuous, pseudo-random, mediolateral platform oscillations. Both the ranges and variability of angular momentum for both the whole body and both legs were significantly greater (p<0.001) during platform oscillations. There were no significant differences between groups in whole body angular momentum range or variability during unperturbed walking. The range of frontal plane angular momentum was significantly greater for those with amputation than for controls for all segments (p<0.05). For the whole body and intact leg, angular momentum ranges were greater for patients with amputation. However, for the prosthetic leg, angular momentum ranges were less for patients than controls. Patients with amputation were significantly more affected by the perturbations. Though patients with amputation were able to maintain similar patterns of whole body angular momentum during unperturbed walking, they were more highly destabilized by the walking surface perturbations. Individuals with transtibial amputation appear to predominantly use altered motion of the intact limb to maintain mediolateral stability.

Keywords: Gait; Stability; Transtibial amputation; Variability; Virtual reality.

Figure 1. Frontal plane angular momentum during NOP

The between-subjects mean ± SD (A – B) and group mean of within-subject variability ± SD (C – D). The whole body angular momentum (A, C) is normalized to Height × Body Mass × Walking Speed. The prosthetic/left leg and intact/right leg (B, D) angular momentum is normalized to Leg Length × Leg Mass × Walking Speed. AB are plotted in blue and TTA are plotted in red. The whole body and prosthetic leg are graphed from prosthetic/left heel strike to prosthetic/left heel strike with the intermediate gait events labeled on the x-axis. The intact leg is graphed from intact/right leg heel strike to intact/right leg heel strike.

Figure 2. Frontal plane angular momentum during PLAT

The between-subjects mean ± SD (A – B) and group mean of within-subject variability ± SD (C – D). The whole body angular momentum (A, C) is normalized to Height × Body Mass × Walking Speed. The prosthetic/left leg and intact/right leg (B, D) angular momentum is normalized to Leg Length × Leg Mass × Walking Speed. AB are plotted in blue and TTA are plotted in red. The whole body and prosthetic leg are graphed from prosthetic/left heel strike to prosthetic/left heel strike with the intermediate gait events labeled on the x-axis. The intact leg is graphed from intact/right leg heel strike to intact/right leg heel strike. The scale on the plots are the same as the NOP Figure 1.

Figure 3. Group mean frontal plane angular momentum variables

The mean range of the frontal plane angular momentum (A – B) and the mean variability over prosthetic/left single support (C – D) and intact/left single support (E – F) for both NOP and PLAT. AB are displayed as blue circles and TTA are displayed as red diamonds. All plots are represent the group means with 1 SD error bars.