Electrical stimulation and denervated muscles after spinal cord injury

Subhalakshmi Chandrasekaran, John Davis, Ines Bersch, Gary Goldberg, Ashraf S Gorgey, Subhalakshmi Chandrasekaran, John Davis, Ines Bersch, Gary Goldberg, Ashraf S Gorgey

Abstract

Spinal cord injury (SCI) population with injury below T10 or injury to the cauda equina region is characterized by denervated muscles, extensive muscle atrophy, infiltration of intramuscular fat and formation of fibrous tissue. These morphological changes may put individuals with SCI at higher risk for developing other diseases such as various cardiovascular diseases, diabetes, obesity and osteoporosis. Currently, there is no available rehabilitation intervention to rescue the muscles or restore muscle size in SCI individuals with lower motor neuron denervation. We, hereby, performed a review of the available evidence that supports the use of electrical stimulation in restoration of denervated muscle following SCI. Long pulse width stimulation (LPWS) technique is an upcoming method of stimulating denervated muscles. Our primary objective is to explore the best stimulation paradigms (stimulation parameters, stimulation technique and stimulation wave) to achieve restoration of the denervated muscle. Stimulation parameters, such as the pulse duration, need to be 100-1000 times longer than in innervated muscles to achieve desirable excitability and contraction. The use of electrical stimulation in animal and human models induces muscle hypertrophy. Findings in animal models indicate that electrical stimulation, with a combination of exercise and pharmacological interventions, have proven to be effective in improving various aspects like relative muscle weight, muscle cross sectional area, number of myelinated regenerated fibers, and restoring some level of muscle function. Human studies have shown similar outcomes, identifying the use of LPWS as an effective strategy in increasing muscle cross sectional area, the size of muscle fibers, and improving muscle function. Therefore, displaying promise is an effective future stimulation intervention. In summary, LPWS is a novel stimulation technique for denervated muscles in humans with SCI. Successful studies on LPWS of denervated muscles will help in translating this stimulation technique to the clinical level as a rehabilitation intervention after SCI.

Keywords: DXA; LMN injury; LPWS; MRI; denervation; electrical stimulation; spinal cord injury; stimulation parameters.

Conflict of interest statement

None

Figures

Figure 1
Figure 1
Seddon’s classification of peripheral nerve injury. Displays three types of injury along the axon of a neuron as compared to a healthy nerve.
Figure 2
Figure 2
Briefly summarizes the anatomy of the conus medullaris and the cauda equina. The Conus Medullaris forms the end of the spinal cord near the lumbar vertebral sections L1 and L2. The cauda equina is comprised of a bundle of lumbar and sacral nerve roots and connects to the conus medullaris.
Figure 3
Figure 3
Dual-energy X-ray absorptiometry scan of the right (A) and left (B) hip joints of a denervated individual with T7 level of injury. Femoral head and bone density deterioration post 6.5 years of injury.
Figure 4
Figure 4
A comparison between two patients with SCI. The right thigh shows dramatic muscle atrophy in an individual with a T12 complete denervated SCI as compared to an innervated individual with SCI (left). SCI: Spinal cord injury.
Figure 5
Figure 5
Placement of the electrodes in a SCI patients with LMN. A rubber-based electrode is covered in a salt free gel (A) before being placed in a wet, conductive sponge (B) which prevents surface tissue damage. The covered electrode is then secured with elastic straps in position above the knee extensor groups (C). LMN: Lower motor neuron; SCI: spinal cord injury.

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