Multi-feature Compensatory Motion Analysis for Reaching Motions Over a Discretely Sampled Workspace

TL;DR

Results indicate that compensatory motions occur mainly in a right trapezoid region in the upper left area and a vertical trapezoid region in the middle left area for right-handed subjects reaching horizontally and vertically, which might guide motion selection in clinical rehabilitation, occupational therapy, and prosthetic evaluation.

Abstract

The absence of functional arm joints, such as the wrist, in upper extremity prostheses leads to compensatory motions in the users' daily activities. Compensatory motions have been previously studied for varying task protocols and evaluation metrics. However, the movement targets' spatial locations in previous protocols were not standardised and incomparable between studies, and the evaluation metrics were rudimentary. This work analysed compensatory motions in the final pose of subjects reaching across a discretely sampled 7*7 2D grid of targets under unbraced (normative) and braced (compensatory) conditions. For the braced condition, a bracing system was applied to simulate a transradial prosthetic limb by restricting participants' wrist joints. A total of 1372 reaching poses were analysed, and a Compensation Index was proposed to indicate the severity level of compensation. This index combined joint spatial location analysis, joint angle analysis, separability analysis, and machine learning (clustering) analysis. The individual analysis results and the final Compensation Index were presented in heatmap format to correspond to the spatial layout of the workspace, revealing the spatial dependency of compensatory motions. The results indicate that compensatory motions occur mainly in a right trapezoid region in the upper left area and a vertical trapezoid region in the middle left area for right-handed subjects reaching horizontally and vertically. Such results might guide motion selection in clinical rehabilitation, occupational therapy, and prosthetic evaluation to help avoid residual limb pain and overuse syndromes.

Figures (12)

• Figure 1: Experiment setup (horizontal placement) and the custom arm bracing system.
• Figure 2: The workflow of this project. A total of 1372 reaching data are collected from 7 subjects under the unbraced and braced condition, reaching the 49 targets horizontally or vertically. The reaching final pose (final joint locations and angles) and subjects' static anthropometry information are used to calculate four compensatory motion evaluation metrics: average joint location deviation, average joint angle difference, group separability score, and group clustering accuracy score. The four components are combined as the Compensation Index and presented in heatmap format.
• Figure 3: The first row includes the nomenclatures of the body segment and the symbolic representations of joint locations. The second and third rows include the nomenclatures, graphic and symbolic representations and Normal Range of Motion (NROM) of the joint movement along each orientation.
• Figure 4: Heatmap representation and the relationship with the grid. The number in each grid indicates the number of the target location.
• Figure 5: Elbow, shoulder, and trunk average joint location deviations.