FES and Peripheral Nerve Injuries: Exploring Benefits of Functional Electrical Stimulation
Let's start with a few definitions of the topics we cover in this article. First if all we will review what a peripheral nerve injury is and then, one of our favourite topics, Functional Electrical Stimulation or FES.
What is a peripheral nerve injury?
A peripheral nerve injury is damage to any nerve located outside of the brain and spinal cord. Basically, we can imagine injuries to arms or legs or for example, the brachial plexus region where the shoulder meets the trunk.
These nerves can affect sensation and motor function (the ability to consciously contract muscle) and are responsible for transmitting signals between various parts of the body and the central nervous system (CNS).
Peripheral nerve injuries can result from a variety of causes, including trauma, cuts, diseases such as diabetes, or compression/crushing of a limb.
Symptoms of a peripheral nerve injury can include numbness, tingling, weakness, or pain in muscles of the affected area. Commonly used treatments for a peripheral nerve injury may include physical therapy, medication, and surgery in severe cases.
We are looking in this article at the specific application of something called Functional Electrical Stimulation (FES) which can play an important role in maximising functional recovery.
What is FES?
FES is a conservative technique of applying forms of electrical stimulation, normally through electrodes placed on the affected muscle. Carefully chosen forms of electrical energy will be designed to trigger muscular contractions in the denervated or paretic (paralysed) muscle. We have many articles on this site describing how we apply low-level electrical currents to the muscle through electrode pairs placed on the skin. By careful selection of the form of FES we can make a muscle contract or relax, ease types of pain or even encourage wound healing.
The application of FES techniques has proven beneficial in enhancing functional recovery in people with spinal cord injuries, peripheral nerve injuries, and many other conditions such as stroke, and cerebral palsy.
In particular, this article explores FES and peripheral nerve injuries, and how this functional electrical stimulation can potentially help with nerve regeneration, muscle strengthening, and functional recovery.
Spinal Cord Injury and FES
The RehaStim/RehaMove 2 is a powerful tool for FES Cycling and for situations when the lower motor neurons are intact
Many of our clients with a spinal cord injury (SCI) have experienced the loss of sensory, motor, and autonomic functions below the level of injury. The injury can be so called “complete” or “incomplete”, and depending on the level of the injury to the spinal cord , the individual may have paralysis or paresis of the lower and upper extremities.
FES is a technique used in patients with spinal cord injuries, for example, with FES Cycling and studies have shown FES to be effective in enhancing muscle activation, and sometimes walking ability, and functional recovery in these patients. FES has been shown to improve gait symmetry, muscle bulk, and muscle strength.
Several studies have also shown the utilisation of FES in the treatment of upper limb motor function after spinal cord injury. Electrical stimulation of the muscles of the upper limb can again be used to improve muscle activation, range of movement, and functional recovery.
In many of these cases, when the so-called lower motor neurons are intact, a stimulator such as the RehaMove system is effective as it relies on activating the intact nerve structures.
Peripheral Nerve Injury and FES
As we noted above, peripheral nerve injuries can be caused by trauma, surgery, or disease.
Injuries direct to the peripheral nerves are not involving the spinal cord but still result in muscle weakness, muscle atrophy, and reduced muscle activation because of the effect on local nerves. Peripheral nerve injuries also commonly result in sensory loss and pain.
When such a local nerve injury occurs the result is “de-nervation” and the commonly available forms of FES such as with the RehaMove system will not work. This is because they rely on the local, within muscle, nerve structure being intact to produce a muscle contraction.
At Anatomical Concepts we use two type of FES unit that can work even with denervated muscle - they can be programmed to make the muscle fibres contract directly. These are the Edition 5 and the RISE stimulator. Both units support stimulation for innervated and denervated muscle. The Edition 5 has additional support for pain applications. Both the case forms are the same so both units look the same but the protocols within them are very different. The Edition 5 is more versatile and the RISE stimulaotr is better for long term denervation situations.
There are a number of benefits from using an FES unit optimised for denervated muscle.
The Edition 5 electrotherapy device produces a wide range of protocols including those for denervated muscle
They can support the maintenance of the muscle structure if re-innervation is expected. Reinnervation can take a long time so this can be very helpful.
They can encourage nerve regeneration
They can provide a better long term health outcome if re-innervation is not expected
Peripheral Nerve Regeneration and FES
Nerve regeneration is a process by which damaged axons in the peripheral nerve regenerate and then re-innervate the target muscle. The regeneration process is regulated by neurotrophic factors and is dependent on the close proximity of the target muscle and the injured peripheral nerve.
Although much of the formal research evidence is based on animal studies, there is a lot of case study evidence that supports the application of FES to enhance nerve regeneration by stimulating the injured peripheral nerve or denervated muscle. FES has been shown to improve functional recovery by enhancing axonal regeneration and motor neuron survival after nerve injury.
Axonal Regeneration and FES
Axonal regeneration is the growth of the axonal sprouts from the proximal stump of the injured nerve toward the distal stump. This process is regulated by several factors, including molecular signaling pathways and the proximity of the target muscle.
FES can improve axonal regeneration by stimulating the target muscle, which provides trophic support and enhances the growth of axonal sprouts. FES has also been shown to enhance motor neuron survival and the differentiation of motor neurons in the injured peripheral nerve. Thus, FES is an effective technique in enhancing axonal regeneration and functional recovery after nerve injury. In the early days of FES application we typically use a bipolar, rectangular pulse train with pulse widths of 200 ms or more. The effect is a low frequency burst of pulses that cause the muscle to twitch in response.
Muscle Atrophy and FES
Muscle atrophy is a process of muscle wasting characterised by the reduction in muscle bulk, strength, and function. Muscle atrophy can be the distressing consequence of a prolonged period of immobilisation, disuse, or simply due to the nerve injury.
Functional electrical stimulation (FES) with the RISE or Edition 5, can be used to prevent muscle atrophy by providing a low-level of electrical stimulation to the denervated muscle. These units are very effective in preserving both the tissue mass and quality providing they are used diligently. In building muscle we start with the twitch contractions mentioned above and then over time introduce a stimulation protocol that produces tetanic muscle contractions that strengthen and build muscle. The pulsewidths are perhaps 40 ms and are such that a frequency of around 20Hz is used.
Reinnervation and FES
Reinnervation is the process by which the injured peripheral nerve regenerates and innervates the target muscle. The process is dependent on several factors such as the proximity of the target muscle to the injured nerve, the degree of denervation, and the duration of denervation.
Functional electrical stimulation (FES) has been shown to enhance the prospects of reinnervation by enhancing the sprouting of axons from the proximal stump of the injured nerve. The stimulation of the muscle also provides trophic support to the regenerating motor neurons, which improves the differentiation and survival of the motor neurons. FES also helps in preserving the motor endplate, which is essential for reinnervation after nerve injury.
Muscle Strength and FES
Functional electrical stimulation (FES) has been shown to improve muscle strength in patients with peripheral nerve injuries by inducing muscular contractions. FES can also enhance muscle strength by improving muscle activation, preventing muscle atrophy, and enhancing muscular endurance. Studies have shown that FES can improve muscle strength by up to 50% in patients with peripheral nerve injuries.
Conclusion
Functional electrical stimulation (FES) is an effective technique in enhancing functional recovery in patients with spinal cord injuries or peripheral nerve injuries. The technique can improve muscle activation, prevent muscle atrophy, enhance muscular endurance and strength, and assist in nerve and axonal regeneration. FES is a non-pharmacologic intervention without significant side-effects, which adds an essential therapeutic option to neurological physiotherapy. Further studies on FES are necessary to comprehend the scope, limitations, and methodology for effective clinical translation.