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Neuroprostheses

Neuroprostheses may provide the most promising gains in arm and hand function to individuals with SCI (Kilgore et al., 2018). Neuroprostheses utilize functional electrical stimulation or myoelectrically controlled systems to move prostheses or robotic end effectors. This is achieved through stimulation of residual motor nerves via transcutaneous, percutaneous, or implanted electrodes (Krucoff et al., 2016). Transcutaneous stimulation utilizes electrodes placed on the surface of the skin to stimulate a motor point of the muscle of interest (Baker et al., 1993; Mortimer 1981, while percutaneous and fully implanted electrodes are placed under the skin or in the muscle to stimulate the motor nerve of the muscle of interest (Cameron et al., 1997; Hoshimiya & Nanda 1989).

A variety of neuroprosthetic systems exist including the Handmaster-NMS-1, BGS, and ETHZ-ParaCare systems. All have been applied successfully as rehabilitation tools to restore grasping function in individuals with SCI. However, the most widely used neuroprosthesis for grasping is the Freehand system. Generally, to control the neuroprosthesis, individuals use an on/off switch or apply analog sensors to generate a desired command. There is usually a time delay of one or two seconds from command issue to grasp execution. Therefore, the speed that an individual can grasp and release objects is somewhat limited. Besides the technological drawbacks of neuroprostheses, an important barrier contributing to the use of neuroprostheses (or lack thereof) is the commercial availability of the device. Despite demonstrated improvements in upper extremity function and QOL following stroke or SCI, only one device is commercially available (Venugopalan et al., 2015). For a full list of the benefits and drawbacks of neuroprostheses, please refer to Table 10.

Table 10: Benefits and Drawbacks of Neuroprostheses Systems

Benefits of Neuroprostheses Drawbacks of Neuroprostheses
  • Induces long term changes within the CNS (Popovic et al., 2002)
  • Used as a rehabilition system to promote recovery and better hand function as a permanent device
  • Augment grasp and manipulation functions required for ADLs.
  • Technology still being developed
  • Application is labour intensive
  • Acceptance of device by patient
  • Implantation may not be successful
  • Surgery
  • Technical and maintenance difficulties
  • Extensive training
  • Donning time (if transcutaneous)
  • Long-term reliability of hand function

Neuroprostheses can increase independence, reduce the need for other assistive devices, and decrease the time it takes to carry out activities of daily living (Kilgore et al., 2018). As such, neuroprotheses are typically used to complete tasks such as eating, drinking and personal hygiene. It is important to note that neuroprostheses are distinct from brain computer interfaces. Neuroprostheses connect any part of the nervous system to a device, whereas BCIs connect the brain with a computer and/or robotic system (Krucoff et al., 2016).

With advances in the technological capacity of neuroprostheses, many studies have examined their use in individuals with SCI. As such, the methodological details and results from 18 studies are presented in Table 11.

Table 11 Neuroprotheses Interventions post-SCI

Kilgore et al., 2018

USA

Pre-Post

N=13

Population: Mean age=37 yr; Gender: males=10, females=3; Time since injury: 5.5 yr; Level of injury: C5 – C6.

Intervention: A surgically implanted myoelectrically-controlled neuroprosthesis was evaluated in 15 arms in individuals with cervical-level spinal cord injury. Outcome measures were assessed at baseline, one and three mo following surgery.

Outcome Measures: Active range of motion; Grip strength; Ability to pick up and release objects.

1.     Stimulation produced active extension and flexion for all five digits in all 15 arms studied, however, no statistics were reported. No subject had any active movement in their fingers or thumbs when the stimulation was turned off.

2.     There was a significant increase in grip strength when the neuroprosthesis was turned on for all individuals (p<0.0001).

3.     Using the neuroprosthesis, all 15 arms could manipulate at least 5 out of 6 objects, whereas only one hand could manipulate 4 objects prior to implantation.

Kilgore et al., 2008

USA

Pre-post

N=3

Population: Mean age: 34.0±9.5 yr; Level of injury: C5=1, C6=2.

 

Intervention: A second generation neuroprosthesis system was implanted into individuals and functional outcomes were evaluated.

Outcome Measures: Grasp and Release Test (GRT), Activities of Daily Living Abilities (ADLAT), Craig Handicapped Assessment and Reporting Tool (CHART), NP Usage Survey.

1.     Functional Outcomes: all three subjects used their NP to perform activities that they could not perform prior to implantation (post implant follow up ranged from 2-4 yr).

2.     Body Structures and Function: every subject improved in pinch force strength; post op pinch force with the NP was significantly greater than without the NP (paired-sample t-test, p=0.038).

3.     Activities: every subject was able to double the number of objects manipulated in the GRT with NP (two subjects completed 6/6 tasks; one subject 5/6 tasks)

4.     ADLAT all three subjects improved in least five activities with one subject in all nine.

5.     Participation: all three subjects increased their scores for physical independence, one in the mobility task, one in the social integration scale, one subject a decrease in occupation subscale.

6.     Device Usage: 2/3 reported daily usage of the NP; 1/3 used the device 50% of the time.

Peckham et al., 2001

USA

Pre-post

NInitial=51; NFinal=50

Participants: Age: 16-57 yr; Gender: males=42, females=9; Level of injury: C5-C6; Mean time since injury: 4.6 yr.

Intervention: Participants were trained to use the neuroprosthesis and to use it for functional activities. Once they were satisfied with their ability to perform daily activities or when they reached a plateau in proficiency then rehab was complete.

Outcome Measures: Pinch strength, active ROM, Grasp-Release Test, Activities of Daily Living (ADL) Abilities Test, ADL Assessment Test & user satisfaction survey.

1.     When the neuroprosthesis was activated all participants increased their pinch force in lateral pinch (p<0.001) and some increased their pinch force in palmar grasp (p<0.001).

2.     98% of participants moved at least one object with the neuroprosthesis (p<0.001) and 37 improved by moving at least three more objects (p<0.001).

3.     Disability was reduced in 49 of 50 participants as measured by the ADL abilities or ADL assessment tools.

Taylor et al., 2001

UK

Pre-Post

NInitial=9; NFinal=8

Population: Age: 31-48 yr; Gender: males=7, females=1; Level of injury: C4-6; Time since injury=43-430 mo; Follow-up time=8-53 mo.

Intervention: Interviews- reviewing use of Neuro Control Freehand System.

Outcome Measures: Amount of Care & The System.

1.     No statistical results reported

2.     Completion of personal care was provided by outside nursing agencies. (mean 11.5 hr/day, range 3-24 hr); four users had additional care from family members (mean 3.4 hr/day, range 2-5 hr); no users claimed that care given by family members had decreased

3.     System-donning external components 5-10 min; most users reported no significant problems fitting the external equipment; two users had problems locating the coil; three locating the shoulder controller; one had persistent problems maintaining the position through the day due to the adhesive tape used becoming detached (four reported this as an occasional problem); four users had problems with skin allergy to the tape or double sided adhesive rings; two users reported that the system made transfers more difficult; three users never stopped using the system due to system failure; some problems with equipment reliability; no change in paid caregiver time; six users felt more
confident when using the system; seven felt their quality of life had improved.

 

 

Carroll et al., 2000

Australia

Pre-post

N=6

 

 

Population: Mean age: 29.1 yr; Gender: males=4, females=2; Level of injury: tetraplegia; Time since injury: 1.2-11.3 yr.

Intervention: The Freehand System – an implanted multichannel neuroprothesis.

Outcome Measures: Pinch forces, Grasp and Release Test (GRT), Activities of Daily Living (ADL) Test.

 

 

1.     There was significant improvement in lateral pinch and palmar grasp force after rehabilitation with and without the neuroprothesis.

2.     Force differences were not found between presurgery and rehabilitation without neuroprothesis.

3.     With neuroprothesis, subjects could grasp, move and release more items in the 30 sec GRT, as compared to without the neuroprothesis.

4.     In 35/48 ADL events, less assistance was used (physically or assistive equipment) with the neuroprosthesis. In 41/48 ADL events, neuroprosthesis use was preferred in all subjects.

5.     After study, 5/6 subjects still used neuroprosthesis daily.

Mulcahey et al., 1997 USA

Pre-post

N=5

Population: Age: 16-18 yr; Level of injury: C6=5, Time since injury: >1yr.

Intervention: Implanted Freehand System.

Outcome Measures: Grasp Release Test, Activities of Daily Living (ADL).

1.     40 electrodes implanted, 37 continued to work, all implant stimulators have functioned without problems with follow up ranging between 16-25 mo.

2.     Grasp Release Test-lateral pinch and palmar grasp forces – Wilcoxon test, FES forces were significantly greater than tenodesis forces for both grasps (p=0.043).

Mulcahey et al., 2004

USA

Case Series

N=4

Population: Age: 13-16 yr; Level of injury: tetraplegia; Time since injury: 4-16 wk.

Intervention: The following muscles were implanted with intramuscular electrodes: Extensor digitorum profundus, extensor pollicis longus, flexor pollicis longus, adductor pollicis, and opponens pollicis for each subject.

Outcome Measures: Muscle Strength-Pinch Force & Hand Function, Performance of Activities of Daily Living (ADL), Satisfaction with + without the Freehand System (Canadian Occupational Performance Measure (COPM)), Upper Extremity Capacity, Quadriplegic Index of Function.

1.     No statistical results reported.

2.     No perioperative complications reported.

3.     Subjects began Freehand System use between 2-5 days after implantation.

4.     Muscle Strength-no subject gained significant strength in any key muscle on their freehand limb.

5.     Pinch Force-with Freehand System – each subject realized significant improvement in pinch force.

6.     Upper Extremity Capacity-first 11 questions – no difference with or without Freehand-last set of questions Freehand System improved scores.

7.     Quadriplegic Index of Function-all subjects increased their level of independence.

 

8.     Freehand System Open-ended Questions-all subjects would repeat implantation.

Alon & McBride 2003

USA

Pre-Post

N=7

Population: Gender: males=7, females=0; Level of injury: C5-C6; Mean time since injury: 6 mo.

Intervention: Subjects practiced with the neuroprothesis daily to regain grasp, hold, and release ability and to restore selected functions of 1 of the 2 paralyzed hands. Subjects were observed 2-3x/wk for 3 wks.

Outcome Measures: Activities of Daily Living (ADL) tasks, Hand impairment measures (two grasp and release tests).

1.     All were 100% successful in using the handmaster in the studied ADL and grasp (hold and release) tasks.

2.     Improvements were noted in strength (0.57±98N to 16.5±4.4N, finger linear motion (0.0cm to 8.4±3.2cm) and Fugi-Meyer scores (p<0.05).

Hobby et al., 2001

UK

Pre-post

N=9

Population: Age: 16-55 yr; Level of injury: tetraplegia.

Intervention: The patients, using an external stimulator, built up the muscles strength in the hand and forearm, to ensure the muscles were in good condition at the time of surgery.

Outcome Measures: Grip Strength, Activities of Daily Living (ADL).

 

 

1.     7/9 use Freehand System daily.

2.     Provided an active grip of some strength which allowed many functional activities.

3.     Increase in self-confidence.

4.     For over 80% of their selected ADL goals, user preferred to be independent with their Freehand system than use previous method or have activity performed by caregiver.

Snoek et al., 2000

Netherlands

Pre-Post

NInitial=10; NFinal=4

Population: Age: 20-65 yr; Gender: males=8, females=2; Level of injury: C4 to C6; Classification: 3-Cu=3, 1-O=5, 2-O=1, 0-O=1; Fitted hand: Right n=6, Left n=4.

Intervention: Training for use of Handmaster.

Outcome Measures: Not specified.

1.     Six people left the study for various reasons (>50%). Over all the four remaining were able to perform several tasks with the Handmaster that they were not able to without it (i.e., 3/4 were able to put the splint on independently).
Mangold et al., 2005

Switzerland

Case Series

N=11

Population: Age: 15-70 yr; Gender: males=9, females=2; Level of injury: C5-C7; Severity of injury: AIS A-D.

Intervention: FES was carried out with a stationary stimulation system and two portable systems (ETHZ-Paracare FES system, and Complex Motion).

Outcome Measures: Videos of functional tasks: hand function tests, Self-designed functional tests, Follow-up query-assessment of muscle strength.

1.     Cervical SCI patients can benefit from transcutaneous FES of hand muscles during rehabilitation with respect to muscle strengthening, facilitation of voluntary muscle activity and improvements of ADL functions.

2.     Surface FES system is more flexible in its application and does not need surgical procedures.

3.     High flexibility in electrode placement, stimulation programmes, and FES control devices is required in order to adapt the system to individual needs.

Memberg et al., 2003

USA

Case Series

N=22

Population: Level of injury: C5-C6.

Intervention: Epimysial or intramuscular electrodes were implanted on the triceps. Following surgery standard stimulation exercise regimens were followed.

Outcome Measures: Elbow extension moments at different elbow positions, Performance in controllable workspace experiments, Comparison to an alternative method of providing elbow extension in these individuals (posterior deltoid to triceps tendon transfer).

1.     Variation in elbow moment across subjects significantly greater than the variance within subjects (ANOVA p<0.001).

2.     10/11 elbows tested elbow moment generated by triceps stimulation at different elbow angles, elbow moment weakest with elbow in more extended position (30º flexion) and peaked with elbow at 90º flexion, significant ANOVA p<0.001.

3.     Elbow moment generated by triceps stimulation at 90º and 120º elbow flexion was significantly greater than elbow moment produced by tendon transfer (ANOVA p<0.05), no difference between elbow extension methods at 30º elbow flexion.

4.     Triceps stimulation and posterior deltoid together provided a greater elbow moment than each method separately, difference significant at each elbow position p<0.05, except at 90º.

5.     Quantitative workspace assessment done on 5 arms, more successful with triceps stimulation, significant for each subject, chi square p<0.05).

6.     Average acquisition time with triceps stimulation less than without stimulation 4/5 arms (3.2-6.4 seconds) and significant in 3/5 arms (unpaired t-test p<0.01) and not for one p=0.076.

Taylor et al., 2002

UK

Case Series

N=9

Population: Mean age: 38.4 yr; Gender: males=7, females=1; Level of injury: C4-C6; Mean time since injury: 10.1 yr.

Intervention: Assessment of the Freehand System.

Outcome Measures: Grasp Release Test, Grip Strength, Activities of Daily Living (ADL), Sensory ability (static 2 pt discrimination).

 

1.     Grasp release test results: increase in the types of tasks that subjects could perform (pre n=1.4) and post implantation (n=5.1 p=0.011).

2.     One-yr post implantation the types of tasks performed was 5.5 p=0.027, without the system it was 1.2 (p=0.028).

3.     Number of repetitions increased post implantation from 12.7 to 37.4 (p=0.028) and without the implant post-implantation (20.2, p=0.046).

4.     At one-yr number of repetitions was increase to 50.5, p=0.046 with the system and without 24.3, p=0.28.

Bryden et al., 2000

USA

Case Series

N=4

Population: Age: 23-48 yr; Level of injury: C5-C6.

Intervention: Participants were implanted with an upper extremity neuroprothesis including a triceps’ electrode to provide stimulated elbow extension. Participants exercised triceps 4-6 hr/session using a programmed electrical stimulation exercise regimen that includes breaks. Participants exercised either nightly or every other night-whatever was best for maintaining an optimal amount of strength.

Outcome Measures: Five overhead reaching tasks, Amount of assistance required to complete the task, Survey of home use.

1.     No statistical analysis was completed.

2.     Passive elbow extension was within normal limits.

3.     With stimulated triceps subjects attained full elbow extension; without it full range was not met.

Wuolle et al., 1999

USA

Case Series

NInitial=42; NFinal=30

Population: Age: 13-53 yr; Gender: males=26, females=8; Level of injury: tetraplegia; Follow-up time: 1 yr.

Intervention: Implemented with a hand neuroprosthesis that provides grasp and release.

Outcome Measures: Standardized test of grasp and release (GRT), Measurements of pinch strength and range of motion, Satisfaction survey, Activities of Daily Living (ADL) survey.

 

 

1.     General Satisfaction: 87% were positive agree or strongly agree, 97% would recommend neuroprosthesis to others, 90% were satisfied with neuroprosthesis, 90% stated neuroprosthesis was reliable, 87% would have surgery again, 80% felt the neuroprosthesis met their expectations, & 77% would pay for the neuroprosthesis if they had the money.

2.     Life Impact: 88% responses were positive for life impact; 90% stated neuroprosthesis improved their quality of life; 87% positive impact on their life (90% reported did not make a negative impact); 83% provided a benefit ADL; 87% responses regarding changes in ADL were positive; 93% participants could perform ADL easier; 93% could perform ADL such as painting and shaving; 90% had increased confidence when performing ADL; 83% could perform ADL more normally; 73% could perform ADL faster.

3.     Independence: 81% of responses were positive; 87% reported they were able to function more independently; 83% used less adaptive equipment; 87% required less assistance from others; 67% felt more comfortable out in the community alone.

4.     Occupation: 57% of responses to occupation questions were positive

5.     Appearance: 87% felt their hand appearance was unchanged or improved.

6.     Usage: used prosthesis median of 5.5 days/wk – ranged from 15 participants (44%) who donned the neuroprosthesis 7day/wk to five participants (15%) who used it less than one day/wk; 24/34 participants (71%) used it ≥4 day/wk; range of usage C4/C5, C5/C5, C6/C6 levels was the same (0-7 day/wk) C5/C6 group – used it most regularly 4-7 day/wk with most participants 8/10 reporting daily use.

7.     Activities: most frequently reported activities included eating, drinking, shaving, brushing teeth, brushing hair, writing, operating a computer, playing games.

8.     Quality of Life: 18/34 positive comments; 1/34 responded neutrally; 1/34 responded negatively.

9.     Improvements: Additional stimulus channels, an implanted command source, smaller, lighter external control unit – easier to don, improve
hand and arm function, make device operable if user is confined to bed.

Kilgore et al., 1997

USA

Case Series

N=5

Population: Age: 28-57 yr; Level of injury: C5-C6; Severity of injury: complete; Time since injury: 2-9 yr.

Intervention: Implanted neuroprosthesis.

Outcome Measures: Grasp force, Grasp-Release Test, Tests of Activities of Daily Living (ADL) (functional independence), Usage Survey.

1.     Pinch force ranged from 8 to 25N, with stimulation and greater than tenodesis grasp alone.

2.     All demonstrated functional grasp patterns and were able to manipulate at least three more objects with the neuroprosthesis; had increased independence and were able to use the neuroprosthesis at home on a regular basis; the implanted stimulator proved to be safe and reliable.

Smith et al., 1994

USA

Case Series

N=5

Population: Age: 13-19 yr; Gender: males=5; Level of injury: C5-C6; Time since injury: 3-72 mo.

Intervention: Intramuscular electrodes were implanted in the upper extremity muscles (Freehand System).

Outcome measures: Breslow test.

 

1.     No predicted difference between electrodes in intrinsic and extrinsic muscles (p=0.93).

2.     Significant differences were predicted between exit sites (p=0.016) + across muscle groups (p=0.047).

3.     Survival likelihoods poorer for electrodes exiting dorsally.

4.     At 90 days after implant survivals probabilities of the finger + thumb extensors + thumb abductors were no significant than that of thumb adductor + flexor muscle groups.

Smith et al., 1996

USA

Case Series

N=5

Population: Age: 13-19 yr; Gender: males=3, females=2; Level of injury: C5=5; Time since injury: 3-72 mo.

Intervention: Implanted Freehand System and tendoesis.

Outcome Measures: CWRU Hand System (Case Western Reserve University), Grasp and Release Test.

1.     With the implanted system and tenodesis each case of improved performance in later sessions was significantly better as compared to the initial session. (p<0.05).

2.     The average grasp forces with FNS increased; the range was from 8.9N (SD+5.2) to 22.5N (SD+8.6) and the palmar grasp forces increases from 2.1N (SD+2.9) to 11.1N (SD+6.0).

Discussion

A multitude of studies have investigated the feasibility and efficacy of neuroprostheses for SCI rehabilitation. Based upon the literature, a variety of neuroprostheses exist including myoelectrically controlled neuroprostheses, the Freehand system, Ness H200, and the EHTZ Paracare system. Despite several differences between these systems, all studies demonstrated that use of the system was feasible and more importantly, efficacious. All of the neuroprostheses used resulted in significant positive functional outcomes for individuals with SCI. However, the commercial unavailability of these devices impacts clinical use greatly.

The Freehand System results in significant positive functional outcomes for individuals with tetraplegia, however, there is limited opportunity for standardized clinical use at this time as the device is not commercially available. In addition, most patients need to undergo multiple surgeries for the implantation of electrodes and other various components of the device in order to gain optimal use of the system. This represents another barrier to the wide spread application of the Freehand System.

The NESS H200 developed by Nathan et al., and produced by Neuromuscular Electrical Stimulator Systems, Ra’anana, Israel is the only commercially available upper limb surface FES system (Ragnarsson 2008; Venugopalan et al., 2015). It has been FDA approved for use with individuals with stroke and SCI. It is predominantly used as an exercise tool for stroke subjects and is commercially available in a limited number of countries (Popovic et al., 2002). The NESS H200 has three surface stimulation channels used to generate grasping function in tetraplegia and stroke subjects. One channel is used to stimulate the extensor digitorum communis muscle at the volar side of the forearm. The second channel stimulates the flexor digitorium superficialis and profundus muscles. The third stimulation channel generates thumb opposition. The system is controlled with a push button that triggers hand opening and closing functions. The system is easy to don and doff. However, there are some limitations in its design: the rigid arm splint does not provide enough flexibility of the electrodes for stimulation of the finger flexors for grasp, and it is a stiff orthosis that fixes the wrist joint angle and prevents full supination of the forearm (Popovic et al., 2002).

The ETHZ-Para Care System was developed collaboratively between ParaCare, the University Hospital Zurich, the Rehabilitation Engineering Group at Swiss Federal Institute of Technology Zurich and Compex SA, Switzerland. The system was designed to improve grasping and walking function in SCI and stroke patients. Surface stimulation FES system is programmable, with four stimulation channels and can be interfaced with any sensor or sensory system. The system provides both palmar and lateral grasps. The device has some reported disadvantages that include a lengthy time to don and doff (seven to ten minutes), and it is not commercially available. The next generation of the device will be called the Compex Motion (Popovic et al., 2001; Popovic et al., 2006). The Compex Motion device is currently available in clinical trials with approximately 80 units available. The Compex Motion stimulator was designed to serve as a hardware platform for the development of diverse FES systems that apply transcutaneous (surface) stimulation technology. One of the main advantages in this system is that it is easily programmable (Popovic et al., 2006).

In summary, neuroprostheses are a promising rehabilitative therapy for SCI. Use of a variety of systems demonstrates significant improvements in hand function and quality of life. However, the lack of commercial availability and invasiveness of surgery are deterrents to its clinical use. Future research should focus on developing an affordable and easily accessible neuroprosthesis system.

Conclusion

There is level 4 evidence (from two pre-post tests; Kilgore et al., 2018 and Kilgore et al., 2008) that a surgically implanted neuroprosthesis significantly improves grip strength/pinch force to enhance hand function and ADLs in individuals with SCI.

There is level 4 evidence (from five pre-post studies; Peckham et al., 2001; Taylor et al., 2001; Hobbey et al., 2001; Carroll et al., 2000; Mulcahey et al., 1997) that the implanted Freehand System results in positive increases in grip strength, grasping and overall independence.

There is level 4 evidence (from two pre-post studies; Alon and McBride, 2003; Snoek et al., 2000) that with sufficient practice using the NESS H200 neuroprosthesis, individuals with SCI may regain grasp, hold and release abilities.

There is level 4 evidence (from eight case series; Mulcahey et al., 2004; Memberg et al., 2003; Taylor et al., 2002; Bryden et al., 2000; Wuolle et al., 1999; Kilgore et al., 1997; Smith et al., 1994; Smith et al., 1996) that the implanted Freehand System increases grip strength, grasping, ADL and function, and overall independence.

There is level 4 evidence (from one case series; Mangold et al., 2005) that the ETHZ-ParaCare neuroprosthesis is flexible (non-surgical) and has significant positive outcomes in rehabilitation and the ability to perform daily living tasks.

  • A variety of neuroprostheses exist that have demonstrated significant improvements in upper extremity function. As technology and surgical procedures advance, these systems may become more affordable and accessible for individuals with SCI.