Bioengineering a
Walk to First


July 2011

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Rob Summers may be the first baseball star who is remembered primarily for a thrilling walk to first base. His historic feat was not a milestone on the diamond, but rather a triumph of biomedical engineering and pure tenacity.

Five years ago, Summers was an up-and-coming pitcher on the nation's top-ranked college team, the Oregon State Beavers, when a freak traffic accident left him paralyzed below the chest. Today, Summers is making headlines as the first paraplegic to do what was heretofore unthinkable—stand up and take steps on his own power. His story, and that of the big-league team of bioengineers, physicians, surgeons, and physical therapists who helped him, will go down in the books for giving the spinal cord injury community real reasons to hope for a practical cure.

Getting to First Base

After the accident, Summers' determination to regain the use of his legs helped him withstand hours of grueling but ultimately fruitless physical training. Then he learned of an exciting new clinical study of a technology originally approved by the U.S. Food and Drug Administration to treat chronic back pain: epidural spinal stimulation.

Rob Summers has now taken his first steps in four years.
Photo courtesy of Rob Summers

The researchers and clinicians leading the study were from top-flight institutions such as California Institute of Technology, UCLA, and the University of Louisville. Their technique had shown early success in restoring voluntary mobility in animal subjects, and they had been searching for the ideal human candidate who could help them translate their findings into clinical use. As a seasoned athlete determined to regain the use of his legs by any means, Summers fit the bill perfectly for this rigorous, multiyear study.

His journey to first base began when surgeons implanted a sheet of 16 electrodes on his lower spine, connected by subcutaneous wires to a receiver placed just below the hip. An external control device is used to send wireless signals to the receiver, which sends pulses to the electrodes. That technology, marketed by Medtronic, New York, NY, was selected because it had already been approved by the FDA. The success of this study will likely lead to the study of other devices more customized to the needs of patients with total paralysis.

Electrical stimulators of the sort that enable Summers to walk cost up to $20,000 and are typically used to relieve pain. Doctors were surprised that it was able to help Summers voluntarily move his legs.
Photo courtesy of University of Louisville

Under stimulation, Summers can do what no one with similar disabilities had done before. He can stand up on his own, at will. He can take steps with assistance. Doctors don't yet know exactly how or why it works, but in essence, they know epidural stimulation helps restore the neural networks involved in locomotion. Even without direct signals from the brain, some signaling pathways appear to remain intact and functional.

Cal Tech's Joel Burdick, the engineering lead on the project, says the goal of the system "is to stimulate the native standing and stepping control circuitry in the lower spinal cord so as to coordinate sensory-motor activity and partially replace the missing signals from (the brain) and shout: 'Get going!' to the nerves."

The results of their work with Summers far exceeded the team's expectations, Burdick says.

Epidural Stimulation

Even before he succeeded in walking, Summers reported that spinal stimulation had improved his ability to control bladder, bowel, and sexual functions. For patients who lack the stamina to train at Summers' level, those benefits alone would significantly enhance quality of life.

The research team did not set out to stimulate movement in the leg muscles. That's been done before. Instead, they believed it would be possible to use epidural stimulation to create an environment for independent, voluntary movement—movement not triggered by direct brain-to-nerve-to-muscle commands but rather by some as-yet-unknown sensory signaling process.

In part because of this athlete's drive to exceed goals, it took only three sessions for Summers to pull off the astonishing feat of pushing himself into a standing, weight-bearing position for nearly a half-hour at a time. With the use of a harness and hands-on help from his therapists, he can take steps on a treadmill. Over time, training and stimulation also helped Summers to move major joints at will.

"The spinal cord is smart," says Susan P. Howley, executive vice president for research at the Christopher and Dana Reeve Foundation, Short Hills, NJ, which helped fund the study. "Absent communication from the brain, it can interpret sensory feedback and send instructions to the legs about movement. What this study suggests is that there are potentially promising new therapeutic approaches for spinal cord repair and recovery in this patient population."

Michael MacRae is an independent writer.

The spinal cord is smart. Absent communication from the brain, it can interpret sensory feedback and send instructions to the legs about movement.

Susan P. Howley, executive VP for research, Christopher and Dana Reeve Foundation

 
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by Michael MacRae, ASME.org