Evolution of Neuroprosthetic Approaches to Restoration of Upper Extremity Function in Spinal Cord Injury

Abstract

Background: Spinal cord injury (SCI) occurring at the cervical levels can result in significantly impaired arm and hand function. People with cervical-level SCI desire improved use of their arms and hands, anticipating that regained function will result in improved independence and ultimately improved quality of life. Neuroprostheses provide the most promising method for significant gain in hand and arm function for persons with cervical-level SCI. Neuroprostheses utilize small electrical currents to activate peripheral motor nerves, resulting in controlled contraction of paralyzed muscles. Methods: A myoelectrically-controlled neuroprosthesis was evaluated in 15 arms in 13 individuals with cervical-level SCI. All individuals had motor level C5 or C6 tetraplegia. Results: This study demonstrates that an implanted neuroprosthesis utilizing myoelectric signal (MES)-controlled stimulation allows considerable flexibility in the control algorithms that can be utilized for a variety of arm and hand functions. Improved active range of motion, grip strength, and the ability to pick up and release objects were improved in all arms tested. Adverse events were few and were consistent with the experience with similar active implantable devices. Conclusion: For individuals with cervical SCI who are highly motivated, implanted neuroprostheses provide the opportunity to gain arm and hand function that cannot be gained through the use of orthotics or surgical intervention alone. Upper extremity neuroprostheses have been shown to provide increased function and independence for persons with cervical-level SCI.

Keywords: functional electrical stimulation; myoelectric control; neuroprosthesis; spinal cord injury; upper extremity function.

Figure 1.

Stimulated range of motion for all 15 hands in the study. Each region represents the median joint range of motion obtained in the study. Movement was obtained for the proximal two joints in all digits for all hands. Range was recorded with the wrist splinted in neutral and stimulation of the lateral (thumb range) or palmar (finger range) pinch. CMC = carpometacarpal joint; DIP = distal interphalangeal joint; MP = metacarpal phalangeal joint; PIP = proximal interphalangeal joint.

Figure 2.

Lateral and palmar grasp force obtained for all 15 hands in the IST-12 study, with comparison to the Freehand cohort. Black line indicates the median and the boxes represent the second and third quartiles. Every hand improved in pinch strength with the neuroprosthesis. Pinch strength without the neuroprosthesis is generally due to passive tenodesis grip. NP = neuroprothesis.

Figure 3.

Grasp and Release Test results of the 15 IST-12 arms studied. Using the neuroprosthesis (NP), all 15 arms could pass at least five of the six objects, whereas only one hand could pass as many as four objects prior to implantation (or after implantation with the NP turned off).