Oct. 09, 2021
Spinal cord injury (SCI) can significantly limit an individual's ability to reach forward or laterally and manipulate objects from a seated position. This movement, which requires leaning from a stable seated position to the limit of stability, followed by a return to an upright sitting position, is an integral part of many activities of daily living (ADL).
To address this problem, researchers from Physical Medicine and Rehabilitation and the Rehabilitation Medicine Research Center at Mayo Clinic and others tested the effects of epidural spinal electrical stimulation (ES) on seated reaching performance in two participants with chronic, complete loss of motor and sensory functions below their thoracic-level SCIs. The researchers also studied how stimulating different electrode locations along the lumbosacral spinal segments impacted participants' reach distance while seated on a mat and in their wheelchairs. The results of this study were published in Frontiers in Systems Neuroscience in 2020. First author Megan L. Gill, P.T., D.P.T., and corresponding author Kristin D. Zhao, Ph.D., are researchers at Mayo Clinic's Assistive and Restorative Technology Laboratory in Rochester, Minnesota.
Background about ES
Over the last decade, spinal electrical stimulation, including ES, has emerged as a promising approach to retrain impaired neurocircuitry and improve function in individuals with upper motor neuron damage. This form of spinal electrical stimulation is thought to facilitate a "central state of excitability" within spinal networks below the level of SCI.
In a separate article published in Nature Medicine in 2018, a team of researchers including Drs. Zhao and Gill demonstrated that ES used in combination with task-specific physical therapy enabled a study participant with complete paraplegia to stand and step independently. In their 2018 article, the study team also noted that this combination of ES plus physical therapy, an intensive program referred to as multimodal rehabilitation (MMR), appeared to facilitate recovery of function in the supraspinal-spinal connectome.
Other published reports also have demonstrated that individuals with SCI who receive ES and perform MMR sessions for multiple days a week over several months can achieve improvements in standing performance, independent weight-bearing stepping activity and trunk stability.
Building on that experience, the co-authors of the Frontiers in Systems Neuroscience article designed their study to focus on reaching abilities.
Methods
To focus on reaching abilities, researchers enrolled two individuals with midthoracic SCI due to trauma occurring more than three years before study enrollment:
- Participant 1 was a 26-year-old man who sustained a traumatic SCI at the T6 vertebral level.
- Participant 2 was a 37-year-old man who sustained a traumatic SCI at the T3 vertebral level.
Both study participants were diagnosed with complete loss of motor, sensory and autonomic functions below the level of injury, a level A on the American Spinal Injury Association Impairment Scale (AIS).
The researchers assessed the participants' reaching performance, with and without ES, at several time points throughout the study using the modified functional reach test. Participant 1 performed 1,164 reach tests over 26 time points, and participant 2 performed 480 reach tests over 17 time points.
Results and conclusions
Overall, the study results demonstrate that ES generated instantaneous improvements in seated reaching performance. The researchers note that the study yielded significant new information about the use of ES in patients with SCI:
- Median reach distances achieved during ES were higher than those achieved without ES for both participants.
- When ES was not enabled, reaching ability returned to its original functional state of paralysis for both participants.
- ES-enabled improvements in the forward reach distances were notably greater than those observed in lateral reach distances, in both mat and wheelchair environments, for both participants.
- ES delivered in the caudal region of the electrode array resulted in greater forward reach distances than those achieved when ES was delivered in the rostral region.
"Overall, these findings suggest that ES could serve as a therapeutic tool for restoring functional motor activity that improves trunk stability and seated reaching abilities," explains Dr. Zhao. "This is an encouraging and significant finding, because currently, the only available interventions are long-term, strenuous exercise programs that have yielded only marginal improvements."
The team's observation that stimulation delivered in the caudal regions produced longer forward reaches than those achieved with stimulation in the rostral regions also is of interest.
"This suggests that unique ES configurations may be needed to enable maximum reaching performance in all directions," explains Dr. Gill. "Learning how to optimize those configurations may become a critical feature in the development of next-generation ES technologies if we want to use ES for enhancing the performance of activities of daily living in individuals with SCI."
"Gaining a better understanding of lower extremity activation patterns during reaching and returning to the upright sitting position could help us learn how to adjust ES configuration to optimize reaching performance," adds Dr. Zhao.
The research team acknowledges that future studies investigating the impact of ES on reaching abilities should include a larger sample size and individuals with different classifications of SCI to determine the generalizability of their results.
For more information
Rehabilitation Medicine Research Center. Mayo Clinic.
Assistive and Restorative Technology: Kristin D. Zhao. Mayo Clinic.
Gill ML, et al. Epidural electrical stimulation of the lumbosacral spinal cord improves trunk stability during seated reaching in two humans with severe thoracic spinal cord injury. Frontiers in Systems Neuroscience. 2020;14:79.
Gill ML, et al. Neuromodulation of lumbosacral spinal networks enables independent stepping after complete paraplegia. Nature Medicine. 2018;24:1677.