Investigating the Validity and Reliability of Inertial Measurement Units for Post-Stroke Upper Extremity Rehabilitation

Abstract

Background: Stroke contributes significantly to the global rates of disability and mortality. A widely recognised consequence of a stroke is motor impairment, including upper extremity impairments. Rehabilitation has a significant role in the improvement of upper extremity functioning. However, the field of rehabilitation care is currently confronted with several challenges. Telerehabilitation, which includes wearable motion sensors such as Inertial Measurement Units (IMUs), offers a promising solution to improve rehabilitation care in a home-based environment. Therefore, the ArmCoach4Stroke (AC4S) project, initiated by the Erasmus Medical Centre and Rijndam Rehabilitation Institute, was established to develop and evaluate a wearable system for upper extremity rehabilitation at home for post-stroke patients.

Aim: As part of the AC4S project, the aim of this thesis was to investigate the test-retest reliability and criterion validity of an IMU-sensor based method, compared to an optoelectronic system, for measuring kinematic metrics of the upper extremity in post-stroke patients.

Methods: The data from two protocols were subjected to analysis: a reliability and validity protocol. During both protocols, participants were equipped with IMUs and executed predefined calibration movements, as well as reaching and lifting exercises. For the validity protocol, patients also wore markers of the gold standard marker-based Vicon system. The measurements of the validity protocol were performed in a laboratory setting, whereas the reliability protocol simulated measurements in an ecological environment. The indices of calibration movements and exercises were selected manually. The orientations of the IMU sensor were estimated and joint angle metrics were calculated for the reaching and reach-and-return phase of movements. A statistical analysis of the metrics was performed to investigate test-retest reliability and criterion validity separately. This involved the use of the intraclass correlation coefficients (ICC) and Spearman correlation coefficients, respectively.

Results: Eventually, 18 participants were analysed for the reliability protocol and 7 for the validity protocol. The reliability protocol yielded ICCs indicating both good reliability (values >0.75) and poor reliability (values <0.5) for some metrics. Significant test-retest differences were identified for certain metrics. The Spearman correlation coefficients for the validity protocol indicated strong correlations (values >0.7). However, the p-values were above the level of significance. The results further demonstrated considerable differences in absolute values between IMU and Vicon joint angles across various metrics.

Conclusion: A large variability and poor-moderate reliability were observed for multiple metrics, indicating underlying issues with the measurements or metric calculations. Substantial differences in absolute joint angle values were evident, not only between Vicon and IMU, but also between test-retest sessions or between patients. This indicates suboptimal orientation estimation, angle definitions or other fundamental problems that need further investigation.