To increase the quality of life of stroke patients, better diagnostics with the ability to identify the cause of motor impairment are needed. Robotic diagnostics increases the resolution of measurements, allows for tracking progress over a longer period, and can be used to evaluate new treatments. The Shoulder Elbow Perturbator (SEP) was developed to improve the diagnostics of post-stroke motor impairment. The SEP has already been tested on patients, showing promising results in identifying the cause of motor impairment, but no SEP system performance analysis has been published. To identify the joint properties of the elbow accurately, the SEP should have a bandwidth of at least 12 Hz. Furthermore, admittance and velocity control are required for various possible experimental tasks. This paper shows that the SEP performs adequately for the desired perturbations and experimental conditions for system identification of the human elbow. The SEP's performance is analysed with multisine signals to determine the bandwidth and endpoint dynamics. The velocity controller bandwidth is 50 Hz, and the admittance controller bandwidth is 65 Hz. Furthermore, the controller is stable. Thus, the SEP meets all the requirements and should be able to provide the desired perturbations and experimental conditions needed for system identification of the human elbow.

Background: Upper limb impairments in a hemiparetic arm are clinically quantified by well-established clinical scales, known to suffer poor validity, reliability, and sensitivity. Alternatively, robotics can assess motor impairments by characterizing joint dynamics through system identification. In this study, we establish the merits of quantifying abnormal synergy, spasticity, and changes in joint viscoelasticity using system identification, evaluating (1) feasibility and quality of parametric estimates, (2) test–retest reliability, (3) differences between healthy controls and patients with upper limb impairments, and (4) construct validity. Methods: Forty-five healthy controls, twenty-nine stroke patients, and twenty cerebral palsy patients participated. Participants were seated with the affected arm immobilized in the Shoulder-Elbow-Perturbator (SEP). The SEP is a one-degree-of-freedom perturbator that enables applying torque perturbations to the elbow while providing varying amounts of weight support to the human arm. Participants performed either a ‘do not intervene’ or a resist task. Elbow joint admittance was quantified and used to extract elbow viscosity and stiffness. Fifty-four of the participants performed two sessions to establish the test–retest reliability of the parameters. Construct validity was assessed by correlating system identification parameters to parameters extracted using a SEP protocol that objectifies current clinical scales (Re-Arm protocol). Results: Feasibility was confirmed by all participants successfully completing the study protocol within ~ 25 min without reporting pain or burden. The parametric estimates were good with a variance-accounted-for of ~ 80%. A fair to excellent test–retest reliability was found (ICC= 0.46 - 0.98) for patients, except for elbow stiffness with full weight support (ICC= 0.35). Compared to healthy controls, patients had a higher elbow viscosity and stiffness during the ‘do not intervene’ task and lower viscosity and stiffness during the resist task. Construct validity was confirmed by a significant (all p< 0.03) but weak to moderate (r= 0.36 - 0.50) correlation with parameters from the Re-Arm protocol. Conclusions: This work demonstrates that system identification is feasible and reliable for quantifying upper limb motor impairments. Validity was confirmed by differences between patients and controls and correlations with other measurements, but further work is required to optimize the experimental protocol and establish clinical value.

In this paper we presented the mechanical design and evaluation of a low-profile and lightweight exoskeleton that supports the finger extension of stroke patients during daily activities without applying axial forces to the finger. The exoskeleton consists of a flexible structure that is secured to the index finger of the user while the thumb is fixed in an opposed position. Pulling on a cable will extend the flexed index finger joint such that objects can be grasped. The device can achieve a grasp size of at least 7 cm. Technical tests confirmed that the exoskeleton was able to counteract the passive flexion moments corresponding to the index finger of a severely affected stroke patient (with an MCP joint stiffness of k = 0.63Nm/rad), requiring a maximum cable activation force of 58.8N. A feasibility study with stroke patients (n=4) revealed that the body-powered operation of the exoskeleton with the contralateral hand caused a mean increase of 46° in the range of motion of the index finger MCP joint. The patients (n=2) who performed the Box & Block Test were able to grasp and transfer maximally 6 blocks in 60 sec. with exoskeleton, compared to 0 blocks without exoskeleton. Our results showed that the developed exoskeleton has the potential to partially restore hand function of stroke patients with impaired finger extension capabilities. An actuation strategy that does not involve the contralateral hand should be implemented during further development to make the exoskeleton suitable for bimanual daily activities.