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. 2022 Jul:2022:1-6.
doi: 10.1109/ICORR55369.2022.9896608.

Design of Spiral-Cable Forearm Exoskeleton to Assist Supination for Hemiparetic Stroke Subjects

Ava Chen, Lauren Winterbottom, Katherine O'Reilly, Sangwoo Park, Dawn Nilsen, Joel Stein, Matei Ciocarlie

Design of Spiral-Cable Forearm Exoskeleton to Assist Supination for Hemiparetic Stroke Subjects

Ava Chen et al. IEEE Int Conf Rehabil Robot. 2022 Jul.

Abstract

We present the development of a cable-based passive forearm exoskeleton that is designed to assist supination for hemiparetic stroke survivors. Our device uniquely provides torque sufficient for counteracting spasticity within a below-elbow apparatus. The mechanism consists of a spiral single-tendon routing embedded in a rigid forearm brace and terminated at the hand and upper-forearm. A spool with an internal releasable-ratchet mechanism allows the user to manually retract the tendon and rotate the hand to counteract involuntary pronation synergies due to stroke. We characterize the mechanism with benchtop testing and five healthy subjects, and perform a preliminary assessment of the exoskeleton with a single chronic stroke subject having minimal supination ability. The mechanism can be integrated into an existing active hand-opening orthosis to enable supination support during grasping tasks, and also allows for a future actuated supination strategy.

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Figures

Fig. 1.
Fig. 1.
Supination exoskeleton worn as a standalone device (Top) and as an integrated supination and hand-opening orthosis to assist grasping (Bottom).
Fig. 2.
Fig. 2.
Diagram highlighting spiral exotendon-routing concept. The tendon (red) is anchored to an orthosis on the dorsal side of the hand, and is guided in a spiral path around the arm via a sheath embedded in a thermoplastic brace (cyan) strapped to the forearm. This cable can be retracted within a hand-turned winch (blue) mounted at the base of the forearm; cable tension imposes supination torques about the wrist.
Fig. 3.
Fig. 3.
Supination is considered in this paper as a distributed-rotation motion along the forearm. The proposed spiral cable mechanism generates relative torque between the hand and proximal region of the forearm (sections highlighted green). Use of the forearm itself as a reference plane enables the device to be wholly contained below the elbow.
Fig. 4.
Fig. 4.
Biomechanics of the supinator muscle: the supinator (purple) anchors to the ulna and humerus, and encircles the radius like a sling before attaching to the bone. Its contraction rotates the radius against the ulna.
Fig. 5.
Fig. 5.
Left: the supination brace and hand orthosis used for this study. Right: assembly and internals of hand-turned cable adjustment mechanism.
Fig. 6.
Fig. 6.
Image series of stroke subject demonstrating usage of cable adjustment mechanism. From left to right: (1) subject wearing device in unlocked state; (2) reaching to turn adjustment dial; (3) tightening mechanism to supinate arm; (4) device fully-engaged, with arm fixed in a near-neutral orientation.
Fig. 7.
Fig. 7.
Top: able-bodied resistive loading results reported as mean and standard deviation aggregated across all five subjects and trials (n = 70). Bottom: aggregated results for Trials 1, 3, and 5 (n = 15, 15, 11) depicting slight degradation of device performance over repeated cyclic strain. (Trials 2 and 4 are not shown to reduce figure clutter.)
Fig. 8.
Fig. 8.
Stroke subject reaching forward while wearing an elastic supinator band (Left) and while wearing the proposed device (Right). Our device assists supination independent of arm extension.
Fig. 9.
Fig. 9.
Stroke subject reaching for (Top) and grasping (Bottom) a bottle. The device enables a functional grasp for lifting the bottle to drink.
Fig. 10.
Fig. 10.
Table II and Left: total extent of inclinometer readings when stroke subject attempts to maintain a vertical (0°) end-effector orientation while performing forward-reach task. Right, Top: photos of stroke subject performing experiment without device assistance (left) and with device fully engaged (right). Without device assistance, the subject has some control over end-effector orientation but cannot bring it out of a fully-pronated position. Engaging the cable mechanism both rotates the hand into a more vertical orientation and allows the subject to better maintain this angle.
See this image and copyright information in PMC

References

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