A soft supernumerary hand for rehabilitation in sub-acute stroke: a pilot study

Abstract

In patients with subacute stroke, task specific training (TST) has been shown to accelerate functional recovery of the upper limb. However, many patients do not have sufficient active extension of the fingers to perform this treatment. In these patients, here we propose a new rehabilitation technique in which TST is performed through a soft robotic hand (SoftHand-X). In short, the extension of the robotic fingers is controlled by the patient through his residual, albeit minimal, active extension of the fingers or wrist, while the patient was required to relax the muscles to achieve full flexion of the robotic fingers. TST with SoftHand-X was attempted in 27 subacute stroke patients unable to perform TST due to insufficient active extension of the fingers. Four patients (14.8%) were able to perform the proposed treatment (10 daily sessions of 60 min each). They reported an excellent level of participation. After the treatment, both clinical score of spasticity and its electromyographic correlate (stretch reflex) decreased. In subacute stroke patients, TST using SoftHand-X is a well-accepted treatment, resulting in a decrease of spasticity. At present, it can be applied only in a small proportion of the patients who cannot perform conventional TST, though extensions are possible.

Figure 1

Rehabilitation setup. (A1) SoftHand-X Supernumerary Robotic Hand and its main subsystems, including the hand hardware and the sensing system used to convert motions of the patient into motions of the robot, top view (A2) and side view (A3), with main system dimensions (in mm). (B) Photographic sequence (B1, B2, B3, B4, B5) of the motion pattern of the supernumerary robotic hand, inspired to the most statistically frequent human hand motion, described in literature as the first postural synergy of grasping. (C) Grip patterns of the soft supernumerary robotic hand conforming to the shape of different objects to achieve a natural-looking grasp posture: (C1) a credit card, (C2) a drinking glass, (C3) a bottle, (C4) a banana, and (C5) a screwdriver. (D) Illustration of the full rehabilitation scenario: a patient (white) is sat comfortably and wears the supernumerary limb (red); a therapist (green) guides the patient in the manipulation of objects (blue) resting on a table. (E) Close-up picture of one of the rehabilitation phases: the patient must reach a plastic cube placed on the table, grab it, and then release it. The physiotherapist supports the arm and forearm, facilitating the patient's proximal movements. The grip and release movements are performed through the robotic hand under patient’s control, without the help of the physiotherapist.

Figure 2

Clinical scores in experimental and control group. (A) Motor section of Fugl–Meyer Assessment for Upper Extremity (FMA-UE) and (B) hand-wrist domain of FMA-UE motor section; experimental group patients P1 to P4 (left), mean and standard deviation of experimental and control group (right). The motor section of FMA-UE is scored out of 66, with sub-scores of 24 for the wrist and hand. (C) Medical Research Council (MRC) for the strength of wrist and finger flexor and extensor muscles for each patient of the experimental group, and (D) means and standard deviation across patients of the experimental group. MRC is rated from 0 = no contraction, to 5 = normal strength. (E) MAS for the wrist flexors and (F) for the finger flexors; patients P1 to P4 (left), mean and standard deviation across experimental and control group (right). The MAS rates muscle tone from 0 (no increased muscle tone) to 4 (rigid flexion or extension). Note that control group data for panels (A), (B), (E) and (F) is available only at T0 and T2.

Figure 3

EMG activity of Flexor Carpi Radialis (FCR) and Flexor Digitorum Superficialis (FDS) produced by passive stretching in the four patients of the experimental group. First vertical dotted line indicates the start of passive stretch of the wrist and fingers, while the second vertical dotted line indicates the end of passive stretch. Spontaneous Tonic Muscle Activity (STMA) is before the first line, Dynamic Stretch Reflex (DSR) is between the two lines, and Static Stretch Reflex (SSR) is after the second line (see “Stretch reflex assessment and measurement”). No EMG activity was detected prior to passive stretch in any patient (i.e., STMA was not found in any patient). Spasticity (i.e., DSR with or without SSR) was present in all 4 patients at T0 in both FCR and FDS, with the exception of patient 3, in whom spasticity was present only in FCR. After treatment (T1), spasticity disappears in patients 1, 2, 4 and decreases in patient 3.