Statistical analysis of timeseries data reveals changes in 3D segmental coordination of balance in response to prosthetic ankle power on ramps

Nathaniel T Pickle,Anne K Silverman,Nicholas P Fey,Jason M Wilken

doi:10.1038/s41598-018-37581-9

Abstract

Active ankle-foot prostheses generate mechanical power during the push-off phase of gait, which can offer advantages over passive prostheses. However, these benefits manifest primarily in joint kinetics (e.g., joint work) and energetics (e.g., metabolic cost) rather than balance (whole-body angular momentum, H), and are typically constrained to push-off. The purpose of this study was to analyze differences between active and passive prostheses and non-amputees in coordination of balance throughout gait on ramps. We used Statistical Parametric Mapping (SPM) to analyze time-series contributions of body segments (arms, legs, trunk) to three-dimensional H on uphill, downhill, and level grades. The trunk and prosthetic-side leg contributions to H at toe-off when using the active prosthesis were more similar to non-amputees compared to using a passive prosthesis. However, using either a passive or active prosthesis was different compared to non-amputees in trunk contributions to sagittal-plane H during mid-stance and transverse-plane H at toe-off. The intact side of the body was unaffected by prosthesis type. In contrast to clinical balance assessments (e.g., single-leg standing, functional reach), our analysis identifies significant changes in the mechanics of segmental coordination of balance during specific portions of the gait cycle, providing valuable biofeedback for targeted gait retraining.

Highlights

Advanced robotic leg prostheses for people with below-knee amputations have been developed[1] that are capable of generating the same magnitude of mechanical power as a biological ankle during the push-off phase of gait[2,3]
Post-hoc pairwise analyses of trunk contributions to frontal-plane H showed a brief period of significantly increased contributions at toe-off (66% gc) on all grades for individuals with transtibial amputation (TTA) using the active compared to passive prosthesis (Fig. 3a, Table 1)
Trunk contributions were more positive just after toe-off in non-amputees compared to individuals with TTA using the active prosthesis at 0° and +10° ramp angles (Fig. 3b, Table 1)

Summary

Introduction

Advanced robotic leg prostheses for people with below-knee (transtibial) amputations have been developed[1] that are capable of generating the same magnitude of mechanical power as a biological ankle during the push-off phase of gait[2,3]. This capacity to actively generate mechanical power during stance (when the foot is in contact with the ground) contrasts with conventional passive energy-storage-and-return prostheses, which absorb elastic energy during loading that is released passively during unloading. The range of sagittal-plane H during prosthetic leg stance is greater in people with TTA using both passive and active prostheses compared to non-amputees at various walking speeds[11,12] as well as on stairs[13] and ramps[14], suggesting either an impaired ability to regulate H or a willingness to compromise stability for the sake of other objectives

Objectives

Methods

Results

Conclusion