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Spinal Cord Stimulation to Improve WalkingWise Young, Ph.D., M.D. W. M. Keck Center for Collaborative Neuroscience Rutgers University, Piscataway
Herman, et al. recently published a study reporting that epidural stimulation of the lumbar spinal cord can facilitate locomotor recovery in a person with spinal cord injury (Hermann R, He J, Luzansky SD, Willis W, Dilli S (2002). Spinal cord stimulation facilitates functional walking in a chronic incomplete spinal cord injured. Spinal Cord 40: 65-68). Download the article (pdf 135 Kb).
Although several news reports have focused their attention on the fact that epidural stimulation allowed a person to walk after spinal cord injury, I believe that the more important story lies in the fact that this study heralds a new, more efficient, and practical approach that will make both supported and independent ambulatory training feasible.
Several studies in the past decade from Germany (Werner, et al. in Bonn) and from several U.S. centers (including Edgarton & Dobkin at UCLA and the Miami Project) have shown that intensive ambulation training using weight support and treadmills can restore locomotor function to significant numbers of people with partial function. As many as 40% of people with spinal cord injury may regain useful and independent walking despite some never having walked after their injury.
Supported ambulatory training, however, is very labor intensive. For somebody who is not walking, at least three therapists may be necessary for the initial phases of the training. One person has to operate and watch the treadmill while two people manually move the legs on the treadmill, until the subject develops automatic stepping behaviors. The training takes several hours a day for many months.
These requirements put such training outside of the reach of many people who may benefit from such training. Consequently, several companies and laboratories have turned their attention to building device that can promote stepping behavior with less labor-intensive interventions. These walking devices include muscle stimulation and robotic devices to move the legs. The cost of these devices are prohibitive.
This report from Herman, et al. suggest that epidural stimulation at L1-L2 activates the central pattern generator (CPG), producing full locomotor patterns. A person with spinal cord injury typically only activate a proportion of muscles that participate in walking. During walking, these muscles are overworked and the gait is inefficient. Epidural stimulation recruits more leg muscles to participate in the gait training, improving both the rate and efficiency of walking.
Epidural stimulation thus not only has the potential of changing household walking to long distance ambulation but the improvements of walking speed, endurance, and efficiency occurred with shorter training periods and the beneficial effects appeared to be lasting. The improvements in gait are dramatic, improving the walking rate from 7 seconds per meter to 3 seconds per meter with 20-30% in energy used for walking.
Some critics may dismiss the significance of this approach to ambulatory training because it would be applicable only to people with incomplete spinal cord injury. However, it is likely that future regenerative therapies will convert many so-called "complete" spinal cord injuries with no motor or sensory function into partial function. The goal of rehabilitation would be to convert partial function to useful function.
More studies are required to demonstrate that these effects of epidural stimulation are applicable to many people. At the recent Socety for Neuroscience meeting in November 2001, Milan Dimitrijevic and colleagues reported the efficacy of epidural stimulation in activating reciprocating gait in 10 patients with spinal cord injury and showing detailed electromyographic recordings indicating the appropriate patterns.
Epidural electrical technology is neither difficult nor expensive to implement. Epidural electrical and a stimulator. The FDA has already approved epidural stimulator for pain control and thus this indicaton for epidural stimulation should not present a significant obstacle.
In summary, epidural spinal cord stimulation can significantly improve both the rate and extent of locomotory function after spinal cord injury, as well as the efficiency of walking. This approach can be applied alongside ambulatory training both on treadmills and overground walking and promises to reduce the cost and duration of training.