David Rushton

Functional Electrical Stimulation and rehabilitation—an hypothesis

Functional Electrical Stimulation (FES), used to mimic a weak or paralysed movement, sometimes is followed by a specific recovery of voluntary power in that movement. The mechanism by which this occurs is unclear, and the presumption has often been that FES may somehow promote adaptive changes in cortical connectivity. However, the unique feature of electrical stimulation is that it activates nerve fibres both orthodromically and antidromically. The antidromic impulse in motor nerve fibres will reach the anterior horn cell, but it can go no further up the neuraxis. If the corticospinal-anterior horn cell synapse is a Hebb-type modifiable synapse (i.e. one that is strengthened by the coincidence of presynaptic and postsynaptic activity), then FES, combined with coincident voluntary effort through a damaged pyramidal motor system, could help to promote restorative synaptic modifications at anterior horn cell level, by this unique adaptive mechanism.

Long-term intensive electrically stimulated cycling by spinal cord-injured people: effect on muscle properties and their relation to power output.

Inactivity and muscular adaptations following spinal cord injury (SCI) result in secondary complications such as cardiovascular disease, obesity, and pressure sores. Functional electrically stimulated (FES) cycling can potentially reduce these complications, but previous studies have provided inconsistent results. We studied the effect of intensive long‐term FES cycle training on muscle properties in 11 SCI subjects (mean ± SEM: 41.8 ± 2.3 years) who had trained for up to 1 hour/day, 5 days/week, for 1 year. Comparative measurements were made in 10 able‐bodied (AB) subjects. Quadriceps maximal electrically stimulated torque increased fivefold (n = 5), but remained lower than in AB individuals. Relative force response at 1 HZ decreased, relaxation rate remained unchanged, and fatigue resistance improved significantly. Power output (PO) improved to a lesser extent than quadriceps torque and not to a greater extent than has been reported previously. We need to understand the factors that limit PO in order to maximize the benefits of FES cycling. Muscle Nerve 38: 1304–1311, 2008

Recruitment by motor nerve root stimulators: significance for implant design

Three paraplegics have been implanted with stimulators of the lumbar anterior roots. Twelve roots were trapped in slots, each with three electrodes, a central cathode and two anodes, but the anodes in all the slots were connected together to reduce the number of wires. Cross-talk between roots was observed at lower levels than expected. Cross-talk was assessed from the ratio of the roots threshold to the threshold of the contralateral response (expected ratio: 72). Two hypothetical reasons for this low ratio were: that the cathode current was not equally shared by the anodes; or that the contralateral responses were reflex. Experiments showed that neither explanation was valid. The ratio of the contralateral to ipsilateral threshold for individual slots (K(1)) was sometimes low because the ipsilateral threshold was high. By taking the ratio of the lowest contralateral response to lowest ipsilateral response, for all roots in each subject (K(2)), the ratio should approach the theoretical value. However, for the two subjects with small slots, it was 7.9 and 15.3, much less than 72, suggesting that the original theory was incorrect. Approximate calculations of the activation function suggest that the reason may be that roots which run close to a slot, but not through it, may pass through a virtual anode region outside the ends of the slots, and that anodal break stimulation in those regions causes the cross-talk. Our estimate is that this cross-talk would be expected to occur at intensities above 5.3 times the cathodal threshold. If the roots are stimulated in pairs, below the levels of cross-talk, experimental results show that the moments obtained in response are additive to within 5%.

Implant provision of key, pinch and power grips in a C6 tetraplegic

An 11-channel multiplexed stimulator of nerves and muscles in the left forearm was implanted for hand control in January 1986 in a 21 year old woman who, after sustaining a C6 spinal lesion 7 years earlier, had voluntary shoulder and elbow movement but paralysed hands, trunk and legs. The patient controls the stimulation via a microcomputer control box and an RF transdermal link. We have investigated the control of her stimulated hand with a joystick under her contralateral hand which she moves from the shoulder and elbow. Since 1986, we have tried a variety of joystick control schemes involving power and key grips. Currently, for grip adjustment, forward and backward joystick movements correspond to thumb extension and abduction, respectively giving in addition both finger and wrist extension, whereas right and left joystick movements yield first closure and thumb opposition/adduction and flexion, respectively. Useful grasps are available by moving the joystick forward and then left (key grip), by moving the joystick backward and left (pinch grip), or by moving the joystick back and right (power grip). Thus, three distinct grips may be selected using these three quadrants of joystick movement. An additional control mode was found to be desirable to augment the patients limited voluntary wrist positioning and provide wrist stability while adjusting finger grip.

Exploring positive adjustment in people with spinal cord injury.

This study explored adjustment in people with spinal cord injury; data from four focus groups are presented. Thematic analysis revealed four themes, managing goals and expectations, comparison with others, feeling useful and acceptance, showing participants positively engaged in life, positively interpreted social comparison information and set realistic goals and expectations. These positive strategies show support for adjustment theories, such as the Cognitive Adaptation Theory, the Control Process Theory and Response Shift Theory. These results also provide insight into the adjustment process of a person with spinal cord injury and may be useful in tailoring support during rehabilitation.

Selecting candidates for a lower limb stimulator implant programme: A patient-centred method

Objective: To develop an effective selection procedure for lower limb functional neurostimulation (LLFNS) for standing in paraplegia.Design: The selection procedure and exclusion criteria were based on the previous experience of two clinical centres with experience of LLFNS.Setting: Two Regional Spinal Injuries units in southern England.Subjects: 254 fully rehabilitated paraplegics living in the community.Intervention: Patients were invited to participate in the programme, and if suitable to subject themselves to a rigorous staged selection procedure from which they could withdraw at any time.Outcome measure: Functionally successful home standing using closed-loop surface electrical stimulation.Results: 57/254 patients were suitable on paper and were accessible. 19 of these (CI=10–28) were interested in the project and attended one of the spinal centres for details. Twelve (CI=5–19) of these fulfilled the selection criteria and started on the training programme; and 10 of them completed the muscle training programme successfully. Seven patients (CI=2–12) achieved closed-loop standing in the laboratory and four patients (CI=1–8) did so at home.

Cost-Effectiveness Comparison of Tizanidine and Baclofen in the Management of Spasticity

AbstractObjective: Baclofen and tizanidine are both used for the treatment of muscle spasticity of spinal origin. Their effectiveness, cost and adverse-effect profiles differ. This paper sets out to estimate the cost effectiveness of each drug, and the impact of changing from baclofen to tizanidine. Design: A simplified but realistic model of physician behaviour and patient response was developed as a decision tree and populated with data derived from the available published clinical comparative trials. We considered patients with spasticity caused by multiple sclerosis or spinal cord injury. The outcome measure used was ‘cost per successfully treated day’ (STD). Costs were estimated from the perspective of the UK National Health Service at 2000 values. Results: Expected cost for a cohort of 100 patients over 1 year was estimated to be £181 545 with baclofen and £211 930 with tizanidine. The estimated number of STDs was 20 192 with tizanidine and 17 289 with baclofen. The overall cost effectiveness of managing spasticity using baclofen and tizanidine was very similar (£10.50 and £10.49 per STD respectively). The incremental cost effectiveness (ICE) of using tinzanidine as an alternative to baclofen for first-line treatment was £10.47 per STD. Sensitivity analysis found the model to be robust to changes in key parameters Conclusion: Drug cost should not be a determining factor in making this treatment choice, as the cost effectiveness ratios are similar for both products.

A reconnectable multiway implantable connector

A well-tried plug-and-socket connector system designed for connecting multichannel implanted cables was adapted so as to allow disconnection and reconnection during surgery. Five different sealing techniques were tested in vitro, and it was found that only one of them had the required qualities of high leakage path impedance (taken as more than one megaohm for the worst sample) after three months of saline soak, together with demountability under surgical conditions. The system has subsequently been successfully implemented in a patient in whom reconnection was required two years after implantation.