Abstract
Spasticity is a common disabling complication caused by the upper motor neurons dysfunction following neurological diseases such as stroke. Currently, the assessment of the spastic hypertonia triggered by stretch reflexes is manually performed by clinicians using perception-based clinical scales, however, their reliability is still questionable due to the inter-rater and intra-rater variability. In order to objectively quantify the complex spasticity phenomenon in post-stroke patients, this study proposed a multi-layer assessment system based on a novel measurement device. The exoskeletal device was developed to synchronously record the kinematic, biomechanical and electrophysiological information in sixteen spastic patients and ten age-matched healthy subjects, while the spastic limb was stretched at low, moderate and high velocities. The mechanical impedance of the elbow joint was identified using a modified genetic algorithm to quantify the alterations in viscoelastic properties underlying pathological resistance. Simultaneously, the time-frequency features were extracted from the surface electromyography (sEMG) signals to reveal the neurophysiological mechanisms of the spastic muscles. By concatenating these single-layer decisions, a support vector regression (SVR)-based fusion model was developed to generate a more comprehensive quantification of spasticity severity. Experimental results demonstrated that the stiffness and damping components of the spastic arm significantly deviated from the nonspastic baseline, and strong correlations were observed between the proposed spasticity assessment and the severity level measured by clinical scales ( R = 0.86, P = 1.67e - 5 ), as well as the tonic stretch reflex threshold (TSRT) value ( R = - 0.89, P = 3.54e - 6 ). These promising results suggest that the proposed assessment system holds great potential to support the clinical diagnosis of motor abnormalities in spastic patients, and ultimately enables optimal adjustment of treatment protocols.
Highlights
S PASTICITY is a motor disorder induced by the hyperexcitability of tonic stretch reflexes [1], resulting in a velocity-dependent increase in muscle tone with exaggerated tendon jerk, as a common clinical manifestation of upper motor neuron syndrome following central nervous system injuries [2]–[4]
We started by investigating the identification reliability of the inertia, damping and stiffness parameters, thereby analyzing the biomechanical variation evoked by external perturbation
The values of inertia component were found to be more clustered than that of the damping and stiffness components across subjects, which can be attributed to the fact that the human upper extremity has a certain inertia, most of the time assumed to be dependent on the structural parameters
Summary
S PASTICITY is a motor disorder induced by the hyperexcitability of tonic stretch reflexes [1], resulting in a velocity-dependent increase in muscle tone with exaggerated tendon jerk, as a common clinical manifestation of upper motor neuron syndrome following central nervous system injuries [2]–[4]. The clinical assessment of spasticity is accomplished by manually perceiving limb resistance based on rating scales (e.g. Ashworth Scale [10], Modified Ashworth Scale (MAS) [11], Tardieu Scale [12], and Modified Tardieu Scale (MTS) [13]). Among these scales for spasticity assessment, MAS is most widely accepted since it has easy-to-use procedures, for example, clinicians judge the amount of muscle resistance during the stretch of patient’s relaxed muscles by using qualitative terms such as no increase (MAS 0), slight increase (MAS 1 and 1+), more marked increase (MAS 2) and considerable increase (MAS 3). The inter-rater and intra-rater reliability of these clinical scales has been questioned due to the intrinsic limitations of “feel the resistance” [14]–[16]
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