Introduction

The NeuroControl Freehand System1,2,3,4,5 from Cleveland, Ohio, USA, is an implanted FES device intended for the restoration of hand function in C5 and C6 level tetraplegics. The device consists of an active receiver/stimulator which is placed in the chest wall in a similar way to a cardiac pace maker. Eight leads come from the receiver/stimulator and pass under the skin to a connector site in the upper arm. Here they are joined to epimyseal electrode leads, passed under the skin from the forearm and hand. Power and control signals are passed through the skin to the receiver/stimulator from a skin mounted coil. The subject controls the device by movement of the opposite shoulder, using a skin surface mounted position detector. Hand opening, closing and strength of the grasp are proportional to the distance moved by the shoulder. Both palmar and lateral grasps are possible, selected by pressing a button on the shoulder controller. Tendon transfer surgery is used to augment the system, typically Brachioradialis to Extensor Carpi Radialis for voluntary wrist extension and Posterior Deltoid to Triceps for elbow extension.

This paper reports the first nine Freehand users in Salisbury. A report of the surgical implementation of the system with the same nine subjects has been published elsewhere.6

Method

The purpose of the clinical assessments was to demonstrate the efficacy of the Freehand system both in terms of standardised measures such as a hand function test and grip strength but also to demonstrate its usefulness in every‐day life by an ADL assessment. Sensory ability was also collected to monitor any possible nerve damage due to the procedure.

Outcome measures

The Grasp Release Test (GRT) was devised by the Cleveland group to quantify changes in hand function following receiving the implant.7 It consists of six tasks, three requiring a lateral pinch and three manipulated with a palmar grasp. They are as follows:

  • Picking up wooden pegs and dropping them in a box.

  • Lifting a 250 gm weight and placing it on a box.

  • Gripping and pushing down a plunger. This device is intended to simulate the act of stabbing with a fork and is calibrated to the standard baked potato.

  • Picking up wooden cubes and dropping them in a box.

  • Lifting a plastic cylinder, the same dimensions as a small juice can and placing it on a box.

  • Lifting a videotape and placing it on a box.

Before the main test a pre-test was used to determine whether it was possible for the subject to perform each task. The main part of the test was completed. It was repeated three times. The order of tasks was randomised to prevent bias due to fatigue. The repetitions that could be achieved with the number of errors in 30 s were recorded for each task.

Grip strength was measured using a modified pinch meter. Three grips were recorded, a lateral grasp, a palmar grasp and a five finger grasp.

Activities of Daily Living (ADL) were assessed by patient goals. Before receiving the implant the subject chose eight activities that they could not perform or wished to improve. Tasks were scored to record the amount of assistance or aids required in the set up, performance, and take down stages of each task.

Sensory ability was monitored using static two-point discrimination.8 The medial and lateral side of each finger and thumb pulp were recorded.

Outcome measure assessments were made prior to receiving the implant and after 1 year of functional use of the system. Additionally, the GRT and grip strength measurements were made at the end of the training period, approximately 3 months post surgery. ADL re-assessments were only made at the post-training stage.

Analysis

Continuous data variables were analysed using Wilcoxon signed rank tests. Statistical significant change was assumed at P<0.05.

Ethics

The local ethics committee approved this study and signed informed consent was obtained from each participant.

Results

Out of the nine freehand users, eight were male while one was female. The mean age was 38.4 years with a mean time since injury of 10.1 years at the time of implantation. At the time of writing the total implant experience was 30 years. Four subjects had an international classification (Table 1) for the implanted side of O0, one of O1, two of OCu1 and two of Ocu2.

Table 1 International classification for tendon transfer surgery

Two subjects discontinued using the system. The first developed a lesion of the posterior interosseus nerve as it passes under the supinator, after 3 months of system use. The lesion, which prevented finger, thumb and wrist extension, was of unknown origin but was not thought to be directly related to the system.

The second subject reported problems with bowel motility, experienced after 2 to 4 days of use, leading to severe constipation. Before being involved in the project, his bowel care was managed by the use of glycerine suppositories every 2 days and Senakot taken the night before. Retrospectively, he reported that loss of reflex activity began while using the external exercise stimulator. Repeated trials of periods when the implant was used and rest periods have confirmed the relationship between bowel activity and stimulation. Bowel emptying ceases after 3 to 4 days of use. We suspect an autonomic function disturbance, possibly raised sympathetic activity inhibiting sigmoid dumping. Beta-blockers were rejected due to the already low blood pressure. Following a literature review it was suggested that nicotine could be used as a colonic accelerator administered using patches. After an initially promising start when use of the system for exercise was possible, the subject became ill and was admitted to hospital for 10 days with symptoms consistent with a UTI. Use of the patches was discontinued and symptoms responded to antibiotics. No causal relationship between the illness and the use of the patches has been established but is still under investigation.

GRT results

Grasp Release Test results are presented comparing test scores pre-implantation with scores with and without the implant at the post-training stage (n=8) and at 1 year post training (n=6) (Table 2). At 1 year the cohort is reduced to six. Subject 3 was unable to use his system following a posterior interosseus nerve lesion and subject 5 had continuing problems controlling the device. GRT results at the post-training stage are sown in Figures 1,2,3,4. All subjects who had completed the training stage showed improvements in GRT score when the system was used. Subjects could perform on average 5.1 types of task (maximum 6) post-implant with the system compared with 1.4 (P=0.010) pre-implantation and 1.5 (P=0.011) post-implantation without the implant. At 1 year the number of types of task was 5.5 (P=0.027) with the system while without 1.2 (P=0.028) could be achieved. There were also significant changes in the total number of task repetitions performed. Subjects could perform on average 37.4 repetitions post-implant with the system compared with 12.7 (P=0.028) pre-implantation and 20.2 (P=0.046) post-implantation without the implant. The number of repetitions was increased at 1 year to 50.5 (P=0.046) with the system and 24.3 (P=0.028) unassisted.

Table 2 Grasp release test
Figure 1
figure 1

This figure illustrates the ability some voluntary wrist extension gives. While only two subjects had ECRL MRC score of 4 or more before surgery, subjects 5 and 7 also had some weak wrist extension

Figure 2
figure 2

This figure illustrates the subject's GRT ability with the system. For those subjects without wrist extension this represents the total gain in function

Figure 3
figure 3

This figure represents the change in ability compared with the subject's ability prior to implantation

Figure 4
figure 4

This figure demonstrates that four subjects demonstrated a change in GRT function even when the system was not used. In subjects 1 and 5 this may be due to improved tenodesis grasp while in subjects 7 and 9 it may be due to reduced wrist flexion following Br to ECRL tendon transfer

Two subjects (1 and 5) showed increased scores in some tasks without the implant. This was due to improved tenodesis grip following Brachioradialis (BR) to Extensor Carpi Radialis Brevis (ECRB) tendon transfer. One subject showed a slight decline in GRT score when using the system for the block test as this task was easier to perform with a tenodesis grasp than with the system. Two subjects showed a decline in the block test without the system. However, both subjects had an effective tenodesis grasp prior to implant and achieved high scores both with and without the implant. The decline may therefore be considered insignificant.

Comparing the individual tasks, five of the six tasks at the post-training stage were performed significantly better post-implantation when the system was used in comparison with pre-op performance (Table 2). The exception is the block task, which was approaching significance at the 0.05 level. Improvement in tenodesis grip of the C6 subjects post-op led to an improvement in the tasks requiring little force when the system was not used. This led to the changes seen in comparison to using the system being non-statistically significant in two of the six tasks although again a trend towards a significant change is present for the can task. Overall performance improved at 1 year in all tasks when the system was used. However, the reduced number of subjects gave fewer statistically significant results.

Overall, the C5 subjects were unable to complete any of the tasks without the system while they could complete most tasks with the system. The C6 subjects could complete some of the tasks involving light objects or little force pre-implantation but could complete all tasks and usually more repetitions with the system.

Grip strength

Grip strength measurements are presented comparing the lateral, palmar and five finger grasp strengths pre-implant with those with and without the implant at the end of training stage and at 1 year. Four subjects had sufficient tenodesis grip to produce a measurable grip pre-implant. They had a mean lateral, palmar and five finger grasp of 0.93N, 0.96N and 1.04N respectively. This was not significantly changed post-implantation when the implant was not used in this subgroup. With the implant post-implantation the mean lateral, palmar and five finger grasp of all eight subjects had increased to 11.2N, 9.5N and 10.4N respectively, all changes shown to be significant (P=0.012) level using the Wilcoxon signed rank test. Grip strength was maintained at 1 year showing a slight increase. The mean lateral, palmar and five finger grasp had increased to 15.2N, 10.4N and 14.7N respectively.

ADL

The most commonly chosen tasks were writing with a pen, using a fork or knife, drinking from a cup and using the telephone. Almost all ADL tasks were achieved at the end of the training period, post implantation. Out of the 64 chosen tasks, on average 3.8 new tasks could be performed by each Freehand System user with adaptive equipment being eliminated from 1.8 tasks. Carer assistance was eliminated from an average of 0.9 tasks while self-assist techniques were discontinued in 1.5 tasks indicating that they were performed in a more normal manner. On average, Freehand users preferred to use their system in 6.5 tasks out of the eight original chosen tasks.

Two point discrimination test

All subjects who had no sensory ability before implantation, all of who had C5 level lesions had no change in their sensory ability as measured by two point discrimination. However, the subjects with C6 level injuries demonstrated some changes (Table 3). Subject 1 showed improved sensation in six areas of the hand, three of which had not demonstrated any sensory ability pre-implantation. Subject 9 had five areas of improved sensory ability as did subject 5. Subject 7, however, who had initially poorer sensation than subjects 1, 5 and 9 recorded a slight reduction in sensation in one area. To test the significance of the measurements the two point scores were ranked, ie npt=0, 1pt=1, 15 mm=2, 10 mm=3, 8 mm=4, 6 mm=5, 4 mm=6 and 2 mm=7. The hand scores for each subject pre-op and at 1 year where then compared using the Wilcoxon Signed Rank Test. Subjects 1, 5 and 9 showed statistically significant changes. While it can not be ruled out that these changes were due to the gradual change in the subjects' neurological condition, as the subjects were 14, 12, 19 and 12 years post-injury at implantation it is reasonable to assume they were in a stable condition. The results suggest that where there is limited sensory ability, increased hand activity may lead to a training effect in sensory ability.

Table 3 Static two-point discrimination

Discussion

GRT

All subjects improved their score on the GRT indicating that the functional ability of their grip had improved. Subjects who had active wrist extension did not improve their score for the lighter tasks but were able to achieve heavier tasks when the system was used. Subjects without voluntary wrist extension were not able to achieve any task without the system but could achieve most tasks when it was used. Some improvements were seen even without the system in those subjects whose voluntary wrist extension had been provided or improved by tendon transfer.

Grip strength

All subjects were able to grip with some force when the system was used. However, the grip provided is approximately 5% of maximum voluntary contraction for normals but this is an order of magnitude greater than was possible using, where possible, their tenodesis grip.

ADL

The ADL results must be examined with some caution as they indicate what was possible rather than what was normal practice for the Freehand user. Nevertheless most ADL goals were achieved and the use of the system preferred in over 80% of activities. Overall the system was most successful for activities that required a moderate amount of force. Activities that required a wide opening of the hand to acquire objects were less successful. While the system allowed new tasks to be performed, other tasks were performed without assistance or without adaptive devices for the first time. This represents an increase in independence for the Freehand user.9

Two point discrimination

Changes in two point discrimination following electrical stimulation have been reported in one other study where 11 subjects who had had a stroke received electrical stimulation to improve wrist and finger extension using skin surface electrodes.10 While improvements in hand function were reported with this group it is possible that the sensation of the stimulation may also have been a factor. The sensation experienced by Freehand users due to the stimulation is considerably less than experienced in the other study so it is possible that this neuroplastic effect may be due to sensory input due to increased use of the hand. This may be similar to the improvement seen in stereognosis seen in cerebral palsy patients following tendon transfer surgery which has resulted in improved hand function.11,12

Conclusion

Seven of our nine subjects are current daily users of their systems and are able to achieve improved function. The system provides an active grasp with strength, enabling relatively heavy objects to be manipulated. This leads to greater independence and quality of life for its users, which could not be achieved by any other means.

Supplier

The Freehand System is CE marked and FDA approved and is available from The NeuroControl Corporation, 8333 Rockside Road, Valley View, Ohio 44125, USA. Tel. 001 216 912 0101.