Segmental contributions to sagittal-plane whole-body angular momentum when using powered compared to passive ankle-foot prostheses on ramps

Abstract

Understanding the effects of an assistive device on dynamic balance is crucial, particularly for robotic leg prostheses. Analyses of dynamic balance commonly evaluate the range of whole-body angular momentum (H). However, the contributions of individual body segments to overall H throughout gait may yield futher insights, specifically for people with transtibial amputation using powered prostheses. We evaluated segment contributions to H using Statistical Parametric Mapping to assess the effects of prosthesis type (powered vs passive) and ramp angle on segmental coordination. The slope main effect was significant in all segments, the prosthesis main effect was significant in the prosthetic leg (device and residuum) and trunk, and the slope by prosthesis interaction effect was significant in the prosthetic leg and trunk. The magnitude of contributions to sagittal-plane H from the prosthetic leg was larger when using the powered prosthesis. The trunk contributed more positive (backward) H after prosthetic leg toe-off when using the powered prosthesis on inclines, similar to the soleus muscle. However, trunk contributions to H on declines were similar when using a powered and passive prosthesis, suggesting that the powered prosthesis may not replicate soleus function when walking downhill. Our novel assessment method evaluated robotic leg prostheses not only based on local joint mechanics, but also considering whole-body biomechanics.

Figure 1

Adjustable ramp used for data collection at the Center for the Intrepid, Ft. Sam Houston, TX, USA.

Figure 2

Sagittal-plane whole-body angular momentum (H) in people with transtibial amputation using a passive and powered prosthesis when walking at ramp angles of 0°, ±5°, and ±10°, reproduced from [3]. Positive values indicate backward angular momentum, negative values indicate forward momentum.

Figure 3

SPM two-way, repeated measures ANOVA results. Rows correspond to main and interaction effects, and columns correspond to a different body segment: the prosthetic (residuum and prosthesis) and intact leg, prosthetic side and intact side arm, and trunk. The SPM {F} values are the F-scores of the ANOVA as a function of time. The dashed red line indicates the critical F-score needed to achieve significance, and is computed using Random Field Theory to maintain α=0.05 [18]. Regions of significant differences are shaded grey.

Figure 4

SPM pairwise comparisons of the sagittal-plane angular momentum contributions of the prosthetic leg (residuum and prosthesis), H_{Leg,Prosthetic}, when using the powered compared to passive prosthesis. Each column is a different slope. Top row shows the mean (±SD) of normalized H_{Leg,Prosthetic} when using the passive (black line) and powered (red line) prosthesis. Bottom row shows SPM{t}, the t-value as a function of time. Dashed red lines show the critical threshold for significance, calculated using Random Field Theory. Shaded regions indicate significant differences.

Figure 5

SPM pairwise comparisons of the trunk contributions to H when using the powered compared to passive prosthesis. Each column is a different slope. Top row shows the mean and standard deviation of normalized contribution to H when using the passive (black line) and powered (red line) prosthesis. Bottom row shows the SPM{t}, which is the t-value as a function of time. Dashed red lines show the critical threshold for significance, calculated using Random Field Theory. Regions where significant differences were found are shaded grey.