Spinal cord injury (SCI) is damage to the critical part of the central nervous system that carries information to and from the muscles and sensory organs of the body. There are two main types of SCI: complete and incomplete. For years it’s been believed that a complete injury, where no movement is possible below the damage, was a permanent sentence of disability. Now, with a recent study published in the journal Brain, that may all be changing, and with it the possibilities for thousands of individuals with complete SCI.

After sustaining an SCI, patients are examined using the ASIA scale. This instrument is used to determine whether any sensory or motor function is present below the level of injury. It’s possible that some motor and sensory functions are present but impaired, that sensory function is present without motor, and vice versa, and finally that neither function is present.

In people with some sensory or some motor function, more studies recently have shown that there is some potential for recovery. Regardless of the likelihood for substantial improvement, the mere possibility represents a huge difference to the patient, and serves to motivate intensive rehabilitation efforts in many cases. Previously it was believed that in patients with complete injury, where no motor or sensory function is present below injury level, the same recovery was impossible. This is a small oversimplification, because it’s possible that an injury is incomplete even if the individual demonstrates no sensory or motor function; this is assessed with nerve conduction studies.

Considering that prognostic difference, it’s clear that any treatment capable of returning movement to patients with complete injuries would not only impact those receiving the treatment, but thousands with complete SCI who had given up hope of regaining the ability to walk. Harkema and colleagues demonstrated that such a treatment does exist, in two subjects with complete motor and sensory loss, and two subjects with complete motor loss and some sensation intact below the injury level.

“This study demonstrates that individuals diagnosed as clinically motor complete can develop functional connectivity across the lesion in the presence of epidural stimulation…Anatomical connections may have persisted after the injury that were previously ‘silent’ because of loss of conduction as a result of disruption of myelin or the ionic channels of the neurons”

Unlike nerves in the peripheral nervous system, nerves of the central nervous system (CNS) do not regenerate after serious damage. The mechanisms for this difference are not completely understood, but the different glial cells within central nerves appear to be a major factor. These support cells, which are critical for development and proper function of the healthy CNS, inhibit regeneration of those same neurons after injury. In contrast, the glial cells of the peripheral system can serve to facilitate reconnection and regeneration when those nerves are damaged.

Based on that understanding, the belief prior to this study was that some small connections must remain intact for recovery to be possible. All four subjects were tested periodically using aforementioned nerve conduction studies to detect any residual connectivity between neurons above and below the level of spinal cord injury; no functional connectivity was present in any subject. Prior to enrolling in the study, patients had received at minimum 80 locomotor training sessions, using a method also developed by Harkema where physical therapists manually assist individuals in advancing their legs while walking over a treadmill.

The treatment program consisted of two components: an epidural electrical stimulator used to alter the excitability of spinal neurons, allowing them to fire with a reduced input from intact neurons above the injury, and an intense, repetitive stand-training program. Specifically, the epidural stimulator was implanted, four subjects were tested for voluntary movement with the stimulator before training, trained through the intensive program, and then tested for voluntary movement again after training.

After the stimulation and stand-training treatment, the four participants with complete motor loss were able to perform small movements under their own volition, when using the epidural stimulator device. Again, in these four individuals with complete motor loss below the level of their injuries, it was considered impossible to regain that voluntary movement.

“These results demonstrate that humans diagnosed with complete motor paralysis can recover volitional motor drive which can drive coordinated, task-specific movements in the presence of lumbosacral spinal cord epidural stimulation.”

These results mean that some connectivity must have remained intact since the time of injury that had not been identified. Because it wasn’t known that some connections were present, these individuals believed that their motor loss was permanent. There are without a doubt many more people living with SCI with the same belief. These findings should give motivation to everyone with complete SCI, because they mean that some connectivity may persist, which in turn means that some amount of recovery, however unlikely, may yet be possible. Much more investigation is needed into where these pathways might be, including but also beyond the corticospinal tract, where many motor neurons are found.

As always, thank you for reading. If you are interested in reading the study and supplemental materials, which not only outline the program but also contain a rich discussion of the implications and possible mechanisms of observed changes, it is available for free.