Abstract
Background. Stroke is one of the most common causes of physical disability worldwide. The majority of survivors experience impairment of movement, often with lasting deficits affecting hand dexterity. To date, conventional rehabilitation primarily focuses on training compensatory maneuvers emphasizing goal completion rather than targeting reduction of motor impairment.
Objective. We aim to determine whether finger dexterity impairment can be reduced in chronic stroke when training on a task focused on moving fingers against abnormal synergies without allowing for compensatory maneuvers.
Methods. We recruited 18 chronic stroke patients with significant hand motor impairment. First, participants underwent baseline assessments of hand function, impairment, and finger individuation. Then, participants trained for 5 consecutive days, 3 to 4 h/d, on a multifinger piano-chord-like task that cannot be performed by compensatory actions of other body parts (e.g., arm). Participants had to learn to simultaneously coordinate and synchronize multiple fingers to break unwanted flexor synergies. To test generalization, we assessed performance in trained and nontrained chords and clinical measures in both the paretic and the nonparetic hands. To evaluate retention, we repeated the assessments 1 day, 1 week, and 6 months post-training.
Results. Our results showed that finger impairment assessed by the individuation task was reduced after training. The reduction of impairment was accompanied by improvements in clinical hand function, including precision pinch. Notably, the effects were maintained for 6 months following training.
Conclusion. Our findings provide preliminary evidence that chronic stroke patient can reduce hand impairment when training against abnormal flexor synergies, a change that was associated with meaningful clinical benefits.
Introduction
Stroke is one of the leading causes of death and disability globally,1,2 resulting in a wide range of physical, emotional, and cognitive consequences.3 Among the most common physical sequela of stroke are hemiparesis and spasticity, two forms of motor impairment that affect daily living and overall quality of life in approximately 80% of survivors.3 Hand impairment, in particular, is often present in the chronic stage after stroke, frequently manifesting itself as both a decrease in finger strength, loss of dexterity (negative signs), and abnormal hand flexion synergy, characterized by a pattern of involuntary motor activation resulting in finger and hand flexion (positive signs).4,5 Indeed, one of the most prominent deficits in hand dexterity is increased finger enslaving, or unintended force produced by the uninstructed fingers. This hand function abnormality is thought to be a direct result of lesions to the motor cortex and corticospinal tract,5,6,7,8,9 as these are known to be critical for the control of independent finger movements (i.e., finger individuation).5,10–13
Previously, we have shown that stroke patients recover both finger individuation and strength relying on separable recovery processes.5 Recovery asymptotes after the first 3 to 6 months, although typically remains far from the level of performance of healthy individuals, especially for the individuation component. Over the past few years, different training and rehabilitation strategies have assessed the effect of finger and hand training as well as virtual reality environments in chronic stroke patients in an attempt to improve deficits in dexterous movement.14–20 Some of these works reported positive gains in clinical measures of hand dexterity. However, these studies cannot distinguish between compensatory maneuvers versus true impairment reduction as the mechanism underlying clinical benefits. Specifically, these studies did not fully assess force control in the finger individuation tasks,14,18–20 used gross measures of hand dexterity and did not report a detailed individuation metric,14,16 and/or did not report post-training long-term retention of clinical outcomes or retention of improvement in finger individuation.14,18,20 In the present study, we use a direct and quantitative measure of finger dexterity5.
The goal of this study was to discern whether true hand motor impairment can be reduced in the chronic phase after stroke following personalized multidimensional training targeting finger dexterity that minimizes the use of compensatory maneuvers to facilitate performance. To this end, we modified a previously published piano-chord-like task13,21 to train finger dexterity by asking participants to practice in an intense manner against their baseline flexion synergy. Task difficulty during practice was adjusted for each participant based on baseline ability, controlling for individual differences in initial weakness and performance. Participants cannot perform this task by recruiting actions beyond their fingers. We tested both the short- and long-term retention of trained and nontrained hand-chord postures. We quantified hand dexterity by measuring finger individuation and also gauged the impact of the training on clinical outcome measures of impairment, activity, and participation. We hypothesized that intensive training focused on moving fingers against abnormal synergies while minimizing compensatory movements, would improve the ability of patients with chronic stroke to individuate their fingers and perform functional tasks better.
Materials and Methods
Participants
We recruited a cohort of eighteen participants with ischemic stroke and hemiparesis (5 female, 13 male; age 61.3 ± 2.1 years, mean ± SEM). We administered multiple screening assessments during the pretest session to determine participant eligibility. We included participants if they met the following inclusion criteria: (1) age 21 years and older; (2) ischemic stroke at least 6 months prior (time poststroke of 49.7 ± 11.4 months, mean ± SEM), confirmed by computed tomography, magnetic resonance imaging, or neurological report; (3) residual unilateral upper extremity weakness; (4) ability to give informed consent and understand the tasks involved; (5) appearance of flexion synergy in the hand, evaluated by observation of a trainee and/or neurologist; and (6) the ability to extend fingers ≥5° from resting position, as evaluated by a stroke specialist. We excluded participants with one or more of the following criteria: (1) cognitive impairment, as seen by a score of <20/30 on the Montreal Cognitive Assessment (MoCA); (2) history of a physical or neurological condition that interferes with study procedures or assessment of motor function (e.g., severe arthritis, severe neuropathy, Parkinson’s disease); (3) inability to sit in a chair and perform upper limb exercises for one hour at a time; (4) participation in another upper extremity rehabilitative therapy study during the study period; (5) terminal illness; (6) social and/or personal circumstances that interfere with the ability to return for therapy sessions and follow-up assessments; (7) pregnancy; and (8) severe visuospatial neglect, as seen by a score of <44/54 on the Star Cancellation Test. Among the screened patients, 3 patients were excluded from the study. One participant had hemorrhagic stroke, one showed cognitive-related issues in understanding the task and could not sign the informed consent, and the third patient did not show residual unilateral upper extremity weakness. For detailed participant characteristics, see Table 1.
| Table 1. Patient Characteristics in the Trained Cohort.a |
Table 1. Patient Characteristics in the Trained Cohort.a
Apparatus to Measure and Train Finger Dexterity
We tested participants’ hand function using an ergonomic device, designed and published previously5, that measures isometric forces produced by each finger (Figure 1A). The hand-shaped keyboard was comprised of 10 keys with force transducers (FSG-15N1A, Honeywell; dynamic range 0-50 N) underneath each key at the position of the fingertips. Downward flexion force exerted at each fingertip was measured at a sampling rate of 200 Hz. The data were digitized using National Instruments USB-621x devices interfacing with MATLAB (The MathWorks, Inc) Data Acquisition Toolbox. Visual stimuli were presented on a computer monitor (22 inches), run by custom software written in MATLAB environment using the Psychophysics Toolbox (Psychtoolbox).22
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Source: https://journals.sagepub.com/doi/full/10.1177/1545968320939563