Implanted neuroprosthesis for restoring arm and hand function in people with high level tetraplegia

Abstract

Objective: To develop and apply an implanted neuroprosthesis to restore arm and hand function to individuals with high level tetraplegia.

Design: Case study.

Setting: Clinical research laboratory.

Participants: Individuals with spinal cord injuries (N=2) at or above the C4 motor level.

Interventions: The individuals were each implanted with 2 stimulators (24 stimulation channels and 4 myoelectric recording channels total). Stimulating electrodes were placed in the shoulder and arm, being, to our knowledge, the first long-term application of spiral nerve cuff electrodes to activate a human limb. Myoelectric recording electrodes were placed in the head and neck areas.

Main outcome measures: Successful installation and operation of the neuroprosthesis and electrode performance, range of motion, grasp strength, joint moments, and performance in activities of daily living.

Results: The neuroprosthesis system was successfully implanted in both individuals. Spiral nerve cuff electrodes were placed around upper extremity nerves and activated the intended muscles. In both individuals, the neuroprosthesis has functioned properly for at least 2.5 years postimplant. Hand, wrist, forearm, elbow, and shoulder movements were achieved. A mobile arm support was needed to support the mass of the arm during functional activities. One individual was able to perform several activities of daily living with some limitations as a result of spasticity. The second individual was able to partially complete 2 activities of daily living.

Conclusions: Functional electrical stimulation is a feasible intervention for restoring arm and hand functions to individuals with high tetraplegia. Forces and movements were generated at the hand, wrist, elbow, and shoulder that allowed the performance of activities of daily living, with some limitations requiring the use of a mobile arm support to assist the stimulated shoulder forces.

Keywords: Activities of daily living; Electric stimulation; Electrodes, implanted; Quadriplegia; Rehabilitation.

Figure 1

A) The IST-12 implantable stimulator-telemeter, with 12 stimulation channels and 2 EMG recording and telemetry channels. B) Intramuscular (bottom) and nerve cuff (top) stimulating electrodes. C) Epimysial (top) and Intramuscular (bottom) EMG electrodes.

Figure 2

Stimulation patterns for the six arm muscles used in the reaching portion of the “eating” movement.

Figure 3

a) Stimulated reaching controlled by neck EMG signals in first subject. b) Stimulated arm flexion and internal rotation controlled by neck EMG signals, allowing the first subject to place a carrot in her mouth. A mobile arm support was used to overcome shoulder stiffness. c) and d) Second subject extending and flexing arm while using a mobile arm support.

Figure 3

a) Stimulated reaching controlled by neck EMG signals in first subject. b) Stimulated arm flexion and internal rotation controlled by neck EMG signals, allowing the first subject to place a carrot in her mouth. A mobile arm support was used to overcome shoulder stiffness. c) and d) Second subject extending and flexing arm while using a mobile arm support.

Figure 3

a) Stimulated reaching controlled by neck EMG signals in first subject. b) Stimulated arm flexion and internal rotation controlled by neck EMG signals, allowing the first subject to place a carrot in her mouth. A mobile arm support was used to overcome shoulder stiffness. c) and d) Second subject extending and flexing arm while using a mobile arm support.

Figure 3

a) Stimulated reaching controlled by neck EMG signals in first subject. b) Stimulated arm flexion and internal rotation controlled by neck EMG signals, allowing the first subject to place a carrot in her mouth. A mobile arm support was used to overcome shoulder stiffness. c) and d) Second subject extending and flexing arm while using a mobile arm support.

Figure 4

A) X-ray showing 3 of the 4 nerve cuff electrodes implanted in the first surgery of the subject 1. B) Nerve cuff electrode placed around the suprascapular nerve. C) Diagram of dual 12-channel stimulator systems in the first subject.

Figure 5

Arm moments for subject 1. a) Axillary and suprascapular nerve cuff electrodes. b) Four contacts of the musculocutaneous nerve cuff electrode. c) Four contacts of the radial nerve cuff electrode. Contacts that recruited the triceps caused elbow extension moments, while contacts that activated the brachioradialis caused elbow flexion moments. Contact 4 was only tested during the percutaneous phase and was not connected to the implanted stimulator.

Figure 5

Arm moments for subject 1. a) Axillary and suprascapular nerve cuff electrodes. b) Four contacts of the musculocutaneous nerve cuff electrode. c) Four contacts of the radial nerve cuff electrode. Contacts that recruited the triceps caused elbow extension moments, while contacts that activated the brachioradialis caused elbow flexion moments. Contact 4 was only tested during the percutaneous phase and was not connected to the implanted stimulator.

Figure 5

Arm moments for subject 1. a) Axillary and suprascapular nerve cuff electrodes. b) Four contacts of the musculocutaneous nerve cuff electrode. c) Four contacts of the radial nerve cuff electrode. Contacts that recruited the triceps caused elbow extension moments, while contacts that activated the brachioradialis caused elbow flexion moments. Contact 4 was only tested during the percutaneous phase and was not connected to the implanted stimulator.