System identification: a feasible, reliable and valid way to quantify upper limb motor impairments

• Published in: Journal of neuroengineering and rehabilitation Vol. 20; no. 1; p. 67
• Main Authors: van de Ruit, Mark, van der Velden, Levinia L, Onneweer, Bram, Benner, Joyce L, Haarman, Claudia J W, Ribbers, Gerard M, Selles, Ruud W
• Format: Journal Article
• Language: English
• Published: England BioMed Central Ltd 25.05.2023; BioMed Central; BMC
• Subjects: Analysis; Arm; Biomechanics; Cerebral palsy; Diagnostics; Disability; Elbow; Elbow (anatomy); Estimates; Extremities, Upper; Feasibility studies; Human performance; Humans; Identification; Limbs; Medical records; Medical research; Methods; Motor Disorders; Motor impairments; Paralysis; Parameter identification; Perturbation; Physiological aspects; Reliability; Reproducibility of Results; Robotics; Spasticity; Stiffness; Stroke; System identification; Upper Extremity; Upper limb; Validation studies; Validity; Viscoelasticity; Viscosity; Netherlands; Biomechanics; Viscoelasticity; Motor impairments; Upper limb; Diagnostics
• ISSN: 1743-0003; 1743-0003
• DOI: 10.1186/s12984-023-01192-x

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. 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). 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 ([Formula: see text]) for patients, except for elbow stiffness with full weight support ([Formula: see text]). 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 [Formula: see text]) but weak to moderate ([Formula: see text]) correlation with parameters from the Re-Arm protocol. 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.