Efficacy of an implanted neuroprosthesis for restoring hand grasp in tetraplegia: a multicenter study.

OBJECTIVE: To evaluate an implanted neuroprosthesis that allows tetraplegic users to control grasp and release in 1 hand. DESIGN: Multicenter cohort trial with at least 3 years of follow-up. Function for each participant was compared before and after implantation, and with and without the neuroprosthesis activated. SETTING: Tertiary spinal cord injury (SCI) care centers, 8 in the United States, 1 in the United Kingdom, and 1 in Australia. PARTICIPANTS: Fifty-one tetraplegic adults with C5 or C6 SCIs. INTERVENTION: An implanted neuroprosthetic system, in which electric stimulation of the grasping muscles of 1 arm are controlled by using contralateral shoulder movements, and concurrent tendon transfer surgery. Assessed participants' ability to grasp, move, and release standardized objects; degree of assistance required to perform activities of daily living (ADLs), device usage; and user satisfaction. MAIN OUTCOME MEASURES: Pinch force; grasp and release tests; ADL abilities test and ADL assessment test; and user satisfaction survey. RESULTS: Pinch force was significantly greater with the neuroprosthesis in all available 50 participants, and grasp-release abilities were improved in 49. All tested participants (49/49) were more independent in performing ADLs with the neuroprosthesis than they were without it. Home use of the device for regular function and exercise was reported by over 90% of the participants, and satisfaction with the neuroprosthesis was high. CONCLUSIONS: The grasping ability provided by the neuroprosthesis is substantial and lasting. The neuroprosthesis is safe, well accepted by users, and offers improved independence for a population without comparable alternatives.

An implanted upper-extremity neuroprosthesis. Follow-up of five patients.

An implanted neuroprosthesis supplying functional neuromuscular stimulation was used to provide grasp and release to tetraplegic individuals. This article describes the results, at a minimum of three years, for the first five patients to have operative implantation of an eight-channel stimulator-receiver. All of the patients had a clinically complete spinal cord injury with motor function remaining at the level of the fifth or sixth cervical nerve root. In addition to implantation of the stimulator system, each patient had augmentative operations on the hand to improve function. The procedures included tendon transfers, side-to-side tendon anastomoses, arthrodesis of the interphalangeal joint of the thumb, and rotational osteotomy of the radius. The neuroprosthesis provides two grasp patterns controlled by voluntary motion of the shoulder or wrist. Functional evaluations included measurement of pinch force, a grasp-release test, evaluation of the level of functional independence, and usage surveys. Pinch force ranged from eight to twenty-five newtons. All five patients demonstrated functional grasp patterns, had increased independence, and were able to use the neuroprosthesis at home on a regular basis. The implanted stimulator has proved to be safe and reliable, with seven years as the longest time in situ at the time of writing.

Development of a quantitative hand grasp and release test for patients with tetraplegia using a hand neuroprosthesis.

We developed a quantitative grasp and release test for assessing a hand neuroprosthesis in C5 and C6 level tetraplegic patients. The objectives were (1) to determine if a patient's hand performance with the neuroprosthesis exceeded a defined, clinically acceptable baseline, (2) to compare performance with and without the neuroprosthesis, (3) to measure the consistency of performance over time, and (4) to compare performance among patients. In the test, patients grasped, moved, and released one of six different objects as many times as possible in five 30-second trials for each object, with and without the neuroprosthesis. Unlike earlier tests, the objects and the task were chosen to span a range of difficulties appropriate for C5 and C6 tetraplegic patients using a hand neuroprosthesis. Data from five patients showed that performance with the neuroprosthesis was above the baseline; performance improved with the neuroprosthesis, although it was not generally consistent across sessions; and the neuroprosthesis helped C5 patients manipulate most objects and helped C6 patients primarily with more difficult objects.

Functional evaluation of quadriplegic patients using a hand neuroprosthesis.

The objective of this retrospective study was to compare the abilities of quadriplegic patients to complete activities of daily living with and without the use of a portable hand neuroprosthesis. The neuroprosthesis provided synthetic hand grasp through functional neuromuscular stimulation of paralyzed forearm and hand muscles. Data were obtained from telephone interviews, patient records, and videotapes. Twenty-two quadriplegic patients were included in the study; 15 were functional at a C5 spinal cord injury level and seven at a C6 level. The median success rate (ie, the percentage of patients who could complete each activity) across the ten activities was 89% with the hand neuroprosthesis but was only 49% without the hand neuroprosthesis. All patients could perform more tasks when the neuroprosthesis was used, although the relative improvement of C5 patients was larger than that of C6 patients.

Electrode characterization for functional application to upper extremity FNS.

A quantitative method has been developed to characterize the isometric force vectors of electrically stimulated paralyzed muscles of the thumb. The vectorial force output as a function of the stimulus level was measured for individual electrode/muscle combinations in a number of intramuscular and epimysial electrodes implanted in paralyzed thenar muscles of cervical level spinal cord injury subejcts. Vectors are used to determine the output characteristics of each electrode/muscle combination. The characteristics studied include: the strength of the contraction, the stimulus level at which fibers from other muscles are stimulated, the recruitment gain of force, dependency of the output on the skeletal position, and the direction of force produced. These characteristics can then be used to select stimulus parameters to produce coordinated hand motion and force generation by functional neuromuscular stimulation (FNS). The range of muscle force and direction for each electrode/muscle combination showed considerable variation between subjects and between electrodes in the same subject. This variation is primarily due to differences in electrode placement within the muscle. Comparison between intramuscular and epimysial electrodes demonstrated similar characteristics in the force vector output. Preliminary results show the potential for using the force vector output to predict the cocontracted output of two muscles.

Synthesis of hand grasp using functional neuromuscular stimulation.

A functional neuromuscular stimulation system has been developed to provide grasp-release function in quadriplegic individuals. A single command input from the subject controls the stimulus levels to a number of electrodes, thus simultaneously activating several muscles. A method for synthesizing the command input to stimulus output relationship has been developed. The first step involves electrode profiling, which is a method for characterizing the output of an individual electrode/muscle combination. The electrodes are then grouped according to function and a set of rule based procedures is used to synthesize the basic grasp parameters. Results are presented demonstrating the output from lateral and palmar grasps developed by this method. The method has successfully resulted in grasping patterns that can be utilized functionally. Limitations of the method and future improvements are discussed.

Implantable functional neuromuscular stimulation in the tetraplegic hand.

Functional neuromuscular stimulation of the upper extremity provides manipulative capacity to persons with high level tetraplegia who have insufficient voluntary muscles available for tendon transfer surgery. We report an enhancement of the technique to include surgical implantation of a multichannel receiver-stimulator, sensory feedback stimulation, and tendon transfers. Tendon transfers were done with spastic, rather than voluntary motors employing standard surgical techniques. The system described has been operational for more than 1 1/2 years.

Functional neuromuscular stimulation neuroprostheses for the tetraplegic hand.

Functional neuromuscular stimulation (FNS) of the C5 and C6 tetraplegic upper extremity has been shown to be a valid clinical tool for restoring controlled movement in the paralyzed hand. The current clinical system consists of a shoulder position transducer controlling an external microprocessor-based stimulator, which excites paralyzed muscle via the peripheral nerve using percutaneous leads or a multichannel, implantable stimulator. Tendon transfer surgery of paralyzed but innervated muscle may augment the neurologically deficient upper extremity by allowing the substitution of stronger motors or the addition of new motors where flaccid paralysis (dennervation) eliminates the usual muscle from a grasp pattern. Sensory feedback in the form of machine state and cognitive information can be provided to the normally innervated C5 dermatome skin by subcutaneous electrodes. C5- and C6-level tetraplegics using FNS can independently perform single-hand manipulative tasks at a level similar to that of subjects with intact C7 roots, although they lack the elbow control.