Estimation of 3D Body Center of Mass Acceleration and Instantaneous Velocity from a Wearable Inertial Sensor Network in Transfemoral Amputee Gait: A Case Study.

Hélène Pillet,Joseph Bascou,Giuseppe Vannozzi,Emeline Simonetti,Elena Bergamini

doi:10.3390/s21093129

Abstract

The analysis of the body center of mass (BCoM) 3D kinematics provides insights on crucial aspects of locomotion, especially in populations with gait impairment such as people with amputation. In this paper, a wearable framework based on the use of different magneto-inertial measurement unit (MIMU) networks is proposed to obtain both BCoM acceleration and velocity. The proposed framework was validated as a proof of concept in one transfemoral amputee against data from force plates (acceleration) and an optoelectronic system (acceleration and velocity). The impact in terms of estimation accuracy when using a sensor network rather than a single MIMU at trunk level was also investigated. The estimated velocity and acceleration reached a strong agreement (ρ > 0.89) and good accuracy compared to reference data (normalized root mean square error (NRMSE) < 13.7%) in the anteroposterior and vertical directions when using three MIMUs on the trunk and both shanks and in all three directions when adding MIMUs on both thighs (ρ > 0.89, NRMSE ≤ 14.0% in the mediolateral direction). Conversely, only the vertical component of the BCoM kinematics was accurately captured when considering a single MIMU. These results suggest that inertial sensor networks may represent a valid alternative to laboratory-based instruments for 3D BCoM kinematics quantification in lower-limb amputees.

Highlights

During the rehabilitation of people with lower-limb amputation, monitoring the kinematics of the body center of mass (BCoM) or the 3D ground reaction forces may reveal crucial information related to gait impairment [1,2,3]
Thighs, shanks and feet are the major contributors to 3D BCoM acceleration for people with transfemoral amputation [44], seven magneto-inertial measurement unit (MIMU) were mounted on these segments and manually aligned with their respective longitudinal axes
The results of the proposed framework are encouraging and suggest that MIMUs may represent a promising alternative to lab-based instruments when the 3D BCoM acceleration or velocity is targeted

Summary

Introduction

During the rehabilitation of people with lower-limb amputation, monitoring the kinematics of the body center of mass (BCoM) or the 3D ground reaction forces may reveal crucial information related to gait impairment [1,2,3]. The application of the segmental analysis method, which consists in modeling the body as a chain of rigid segments with known inertial properties, allows obtaining first the trajectory of the segments’ centers of mass and, following a weighted average, that of the BCoM [11] This method has been widely used in the literature for the estimation of BCoM displacement, velocity and acceleration, with some authors proposing optimal marker sets to facilitate the implementation of the method in the clinical field [12,13,14,15]. Both these methods constrain the acquisition to occur in a dedicated laboratory, which may not be adapted to clinical routine due to high system cost and complexity [17], and may result in the acquisition of a few steps only, especially when the force-plate-based method is adopted [2]

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