Guide for participants on paraplegic muscle retraining and standing programmes
This guide describes the work being carried out at in the Department of Medical Physics and Biomedical Engineering at Salisbury District Hospital into the application of electrical stimulation (ES) with persons disabled by spinal cord injury (SCI). Primarily there are two programmes:
to retrain muscles as part of a treatment programme
to enable paraplegics to stand, for therapeutic or functional reasons Electrical stimulation is explained in some detail, with the potential benefits and possible problems you may encounter. The two programmes are then described.
Electrical Stimulation (ES)
What is ES ?
ES produces muscle contractions by artificially introducing a train of electrical impulses into the nerve that supplies the muscle, replacing the impulses that would have come from the brain before the spinal cord was damaged. It is done by placing electrodes on the skin surface, over the muscle in which you wish to produce a contraction. The electrical current passes from the first electrode, through the skin and underlying muscle and back to a second electrode. The electric field produced depolarises the membrane of the nerves that supply the muscle and the resulting impulse is propagated along the nerve which triggers the muscle to contract. This occurs in exactly the same way as non-paralysed muscle under voluntary control, using the bodies own energy supply to power the contraction. ES therefore only triggers the contraction, it does not power it. Each muscle fibre can be only either fully contracted at one strength or fully relaxed. Therefore, the strength of a contraction can only be increased by having more fibres contract or by getting the same fibres to contract more often. The number of fibres contracting can be increased by either increasing the amount of current or the duration of the stimulation pulse, so that the electric field penetrates deeper into the muscle. The number of times the fibre contracts can be increased by increasing its frequency. In practice a compromise is worked out between these parameters. The sensation of ES is a little like ‘pins and needles’. While it would not be fair to describe the sensation as entirely pleasant, those participants who have sensation quickly become accustomed to it.
Who can use ES in these programmes ?
In these programmes, ES is used to stimulate lower limb muscles. In order for
ES to work, the nerve supply to the muscle must be intact. At T12 the nature
of the spinal cord changes from a unified cord, with nerve roots emerging from
it, to a bundle of nerves which connect directly to the muscles. Any damage
below this level is therefore likely to cause damage to the nerves themselves
and prevent the stimulation from working. In practice, denervated muscle can
be stimulated but this requires a different type of stimulation (this is not
described in this guide). For acceptance onto these programmes, candidates must
be of good general health and have no other serious medical complications. Because
ES is used to move the legs, candidates with lower limb contractures or unstable
joints may be excluded. Other excluding factors may be those who suffer from
autonomic dysreflexia, those with cardiac pacemakers and those who are pregnant.
Beneficial effects of ES
The physiological effects of ES are still being assessed. However the following effects have been observed:
Increased muscle bulk: Following SCI, the paralysed muscles start to waste. The quadriceps depth is reduced by about three fifths, but measurements have shown that ES can reverse this decline, even up to the level before the SCI. This has obvious cosmetic appeal but also has physiological consequences, such as reducing the risk of developing pressure sores because of the increased cushioning effect of the muscle over bony protrusions.
Increased blood flow: Similarly, thigh blood flow is reduced to about two thirds of normal and can also be increased to original levels by ES. This improves the flow of blood back up to the heart, because the contracting muscle has a pumping action on the veins. Benefits include an improvement in the skin condition, reduced chance of developing pressure sores, warmer legs and reduced swelling at the feet.
Increase in bone mineral content: Due to disuse many SCI persons may develop a degree of osteoporosis. It has been reported by some researchers that ES can reverse this decline, but our limited
studies do not significantly support this.
Improvement in general health: Some people have claimed that their general
health is improved by regular exercising with ES and that they suffer from fewer
colds and urinary tract infections. These subjective claims are difficult to
assess, but probably arise from the increase in cardiovascular output.
Potential problems with ES
ES is a safe and well tested technique, however there are some potential problems. Often, because muscles become stronger with exercise, spasms will also be stronger. Though it is not normal for spasms to become more frequent. Spasms are generally reduced for a period after exercise, the amount of relief varying from person to person. If spasms become so strong that they interfere with normal activities or if there is any detrimental change in the pattern of spasms then this may be a reason to discontinue using ES. Occasionally some people have an allergic reaction to the electrodes. It is normal to have a slight reddening of the skin under the electrodes after stimulating, due to enlargement of the skin capillaries. If this reddening persists for more than about thirty minutes after use or if you notice any abnormal swelling then you would need to stop stimulating.
Paraplegic standing programme
All SCI persons are encouraged to stand passively on a regular basis, both during rehabilitation following their injury and once they have been discharged from hospital. There are a number of reasons why standing is encouraged; to prevent lower limb contractures, reduce the risk of fractures by minimising the development of osteoporosis, control spasticity, remove pressure from the pelvis, aid in the psychological rehabilitation of the patient and improve the blood circulation. Methods commonly used to stand SCI persons include the tilt table, the Oswestry Standing Frame and lower limb orthoses, such as calipers, Hip Guidance Orthosis and Reciprocal Gait Orthosis. ES has increasingly been investigated as a means of providing both standing and walking for paraplegics. It has several advantages over conventional techniques, in that the equipment is small and cosmetically more acceptable, not involving a large exoskeleton, and that it utilises the person’s own musculature. Standing may be for
therapeutic or functional reasons. When ES is used to produce a function, such
as standing, it is known as Functional Electrical Stimulation (FES). We are
currently engaged on two research programmes to investigate using FES to assist
paraplegics to stand. The two are inextricably linked’ one using surface
electrodes to stimulate the muscles and the other using an implanted stimulator
to stimulate the nerve roots as they exit the spinal cord.
Acceptance onto these programmes
It is important to note that there is a strict selection criteria for these programmes and not all paraplegics will be suitable. Candidates need to be at least one year post injury, have completed a normal hospital rehabilitation programme and have a complete mid-to-low thoracic lesion. Lesions below T12 generally result in denervated muscle and high level lesions may have inadequate voluntary muscle to maintain balance while standing. For any prospective candidate, their relevant medical records will be examined by the team
and discussed with their GP or spinal consultant. A meeting is then arranged,
at which the programme is fully explained, along with contraindications, possible
side-effects and the amount of time and effort required. A physical assessment
is carried out and the muscles are stimulated to ensure that the muscle is not
denervated. If the candidate is suitable and wishes to enter onto the programme,
consent is obtained. A bone density scan is arranged to assess for osteoporosis.
The subject then enters a muscle retraining programme, similar to that described. However, in this case, because the subject is aiming to stand,
it is imperative that they are fully committed. In addition, the gluteals need to be stimulated - despite the inconvenience in their fitting. Generally, a minimum three month period of retraining is performed, though for some subjects this may need to be increased. Assessments are more frequent than in the treatment programme, approximately every two weeks, and additional tests may be added to investigate other phenomenon. After this period, most subjects are strong enough to stand - the force required to stand being related to their body weight. In this way we try to ensure that it is safe to stand before attempted.
Surface FES standing
Since the mid-1980’s, Salisbury District Hospital has developed a standing
system, in conjunction with the Universities of Bath and Surrey and the Royal
National Orthopaedic Hospital, Stanmore. The standing system uses a computer
controlled neuromuscular stimulator with a portable standing frame.
The stimulator is small and is carried under the seat of the wheelchair for convenience. It delivers stimulation through surface electrodes on the skin - stimulating the quadriceps muscles to stand and the gluteal muscles to provide hip stability. The stand is continually monitored by measuring the knee angles using sensors worn in knee cuffs. The stimulator has a closed-loop control algorithm, which detects and corrects for deviations in the knee angles. The stimulator therefore adapts to changes in posture; such as during fatigue, spasms or voluntary postural changes. This process happens so rapidly that the user is usually unaware of any movement. The standing frame can be used as a balance aid, in or outside the home, and is attached to the
wheelchair. It is designed for ease and quickness of use and does not impede wheelchair accessibility. Consequently, the system can be used without supervision, at any location the user may choose, and provide the option for the user to have one hand free for functional tasks. Standing times of up to one hour have been recorded for a single stand, but it is more usual to train subjects to stand several times during the day, say up to a dozen stands each of less than 10 minutes. This is long enough to reach objects from high shelves or order a drink from a bar - therefore the device can be said to provide a useful function. The electrodes and knee angle sensors can be worn all day enabling the user to stand at any time.
To get to the stage of standing at home, subjects need to successfully complete the retraining programme and then attend weekly/fortnightly sessions over three months to practice standing (times approximate). This is required to obtain the correct posture and balance. As confidence is gained the subject is given simple tasks to do such as scratching his ear, reaching forward
and backwards, or drinking from a beaker. These sessions are also for the team to gain experience and optimise the closed-loop control parameters used in standing. The subject may then progress to standing at home. Though follow-ups are still important, visits become more infrequent (say every 2 months). It is important to emphasise that although safety is the central and most important design criterion, ultimately the safe use of the system is dependent on the user operating the system responsibly, as well as the equipment functioning properly. If the equipment should fail, this could lead to the user falling. To date, 23 complete lesion paraplegics have stood successfully with this system, 14 of whom have gone on to use it at home. Some have used it for therapeutic reasons alone, but most have attempted to use it functionally.
Implanted FES standing
Though the surface system has been successful, there are limitations to the system - primarily the requirement to wear electrodes and the time taken to don/doff them. With University College London and the Royal National Orthopaedic Hospital, Stanmore, we have been working on a programme using an implanted stimulator (Lumbosacral Anterior Root Stimulator Implant - LARSI) to provide lower limb functions with paraplegics by stimulation of the lumbosacral anterior nerve roots as they exit the spinal cord. This has received funding from different bodies since the early 1990’s.
Potential advantages are that ‘all’ muscles supplied by lumbosacral nerve roots can be activated. Therefore, it has the potential for us to develop more advanced manoeuvres such as stepping. It may also be possible to stimulate in such a way that different muscle fibres are activated sequentially, thus reducing the effects of fatigue. Potential problems include surgical (accidental surgical damage to the nerve roots could take a few months to recover; cerebrospinal fluid could leak along the implanted cables requiring the subject to have bed rest or surgical repair), implant (faults in the implant have been estimated to occur on average every 15 years; infections in the implant are rare but would mean that the implant had to be completely removed for at least a year)
and movement (the complex nature of the lumbar plexus means that stimulation of each nerve root is likely to result in combined movements at the joints).
The system comprises a multichannel implantable stimulator with a dedicated control language, which has been built at University College London. It is similar in principle to the Sacral Anterior Root Stimulator Implant (SARSI) or ‘bladder stimulator’ which 700 SCI persons have had implanted with a 90% success rate. The electrodes are attached to the anterior nerve roots and connected by flexible cables to an implanted receiver. The receiver is located subcutaneously on or just below the lower part of the rib cage, leaving a profile of approximately 1/2 cm above the skin contour. It is controlled by radio telemetry from an external transmitter, positioned on the skin over the receiver and programmed from a control box worn adjacent to it.
Before a candidate can be considered for an implant they need to have had successfully
completed the surface standing programme for a period of at least nine months
(3 months exercising, 3 months standing in the hospital, 3 months standing at
home - times approximate). Only those who are able to sustain a good posture
and who are willing to commit sufficient
time for testing procedures after the operation will be offered the option
of proceeding to the implanted system. The surgery takes approximately 6 hours,
requiring a hospital stay of 2-3 weeks, and leaves scars of 15 cm over the lumbar
spine and 7cm over the ribs.
Tests on the implant commence within a week of the operation. The subject will use the implant just to maintain muscle bulk in the first few weeks at home and attend weekly sessions to undergo further tests. We assess the sensitivity of each nerve root and then attempt to establish the relationship between the motor nerve roots and the forces that can be produced when they are stimulated. The primary tool used in this is the ‘multi-moment chair’, a purpose built force-rig in which the subject is supported whilst these measurements are made. Using the
results from these tests, the combination of roots to stimulate and at which levels is programmed into the stimulator and this is tried in clinical sessions. Because there are many permutations of these twelve roots, this can be a very time consuming process. It is therefore important to stress the commitment required by the subject. As before, standing is first mastered in the hospital before the system is used at home. After the initial stage of assessing root responses following implantation, the subject may be required to attend sessions in the hospital every two weeks. To date, 2 subjects have been implanted with a LARSI. The first is standing at home and the second is still undergoing testing following surgical nerve damage. We have also successfully tried different functions with our first subject, such as stepping and using a recumbent tricycle.
We will of course make every effort to ensure a successful outcome for each candidate, but we must make it clear that it is in the nature of such projects that results can not be guaranteed and that there are risks associated with the system. We aim to continually improve all our programmes offered to paraplegics and extend these into the general rehabilitation of paraplegics. To meet this, we therefore regard all subjects as being of prime importance. In a very real sense it is a partnership between the subjects and the researchers and we rely on your dedication for the furtherance of this work. If you have any comments or suggestions relating to this document or the programmes described they will be most welcome.
If you wish to know more please do not hesitate to contact us at:
Department of Medical Physics and Biomedical Engineering
Salisbury District Hospital, Salisbury, Wiltshire SP2 8BJ
Tel: 01722-336262 Extn. 4065