For more than 20 years, clinicians working with children with cerebral palsy have been gathering “a deluge of data” to understand and treat their patients’ walking difficulties. But they still weren’t sure which children with the brain disorder would most benefit from intensive corrective surgeries to muscles, tendons and bones intended to help them move more smoothly and efficiently.
In fact, the orthopedic surgeries — which can require months of therapy and recovery —result in significant improvement in only 50 percent of the children. Some kids are even made worse.
Now researchers from the University of Washington’s Department of Mechanical Engineering have analyzed pre- and post-operative data collected over two decades from 473 children with cerebral palsy.
In collaboration with scientists at Gillette Children’s Specialty Healthcare in St. Paul, Minn., the UW engineers have used that analysis to create what they’re calling the Walk DMC, an assessment tool that uses routinely collected electromyography (EMG) data to identify which kids are the strongest candidates for surgery — and to help develop alternative treatments for children needing a different solution.
“It was clear that we were collecting all this data,” said Kat Steele, a UW assistant professor of mechanical engineering. “But more data is not necessarily a good thing. A lot of [its value] comes in how we interpret it.”
Cerebral palsy is caused by a brain injury shortly before or after a baby is born, and affects approximately three children in 1,000. The injury disrupts normal physical development, potentially resulting in weakness, shorter muscles and tendons, and skeletal deformities that can make walking difficult or even impossible. The orthopedic surgeries, which are generally performed around ages 7 to 12, aim to correct some of those issues and improve movement.
The problems with walking and other movement are not, however, caused by abnormalities in the musculature and bones alone. Motor control — the brain’s ability to activate and relax muscles and coordinate motion — plays an essential role in movement, and these skills vary widely in children with cerebral palsy.
“It’s a very complex problem,” said Steele, who is a co-author of a paper explaining the Walk DMC metric published this month in the journal Developmental Medicine & Child Neurology.
“You can have two individuals who are walking visually nearly identically,” she said, “but how they’re controlling that motion can be very different.”
Many of the clinicians working with cerebral palsy patients over the years have believed that motor control plays a major role in determining who benefits most from orthopedic surgery, but their ability to quantitatively assess a child’s motor control was difficult, Steele said.
The Walk DMC — an acronym for the Walking Dynamic Motor Control Index, and a play on Run-D.M.C., a seminal New York hip-hop group — is calculated using EMG data collected when a child is walking. It comes from sensors that detect the independent activation of different leg muscles. The calculation results in a score that indicates how close or far a child’s motor control is from typical development.
Bruce MacWilliams is a biomechanical engineer and orthopedic specialist at Shriners Hospitals for Children in Salt Lake City. MacWilliams, who was not part of the study, said they conduct EMGs in initial assessments with children, but were not relying heavily on the tool to guide their treatment plans.
That’s already changed, he said, with the creation of the Walk DMC score.
“We’re going to put EMGs on everybody,” MacWilliams said. “There is more research to do, but it is very promising. It has changed our practice.”
In addition to the challenges created by the fact that brain injuries are different from person to person, walking — an act most of us don’t think twice about — is actually a complicated set of movements. With each step some muscles are contracting while others relax and then their roles flip in a symphony of coordinated movement.
One of the more common walking patterns in children with cerebral palsy is called crouch gait in which they walk with flexed hips, knees and ankles, causing them to move in a crouched position.
In one child, crouch gait could be caused by shortened muscles and tendons while their motor control is good, resulting in a nearly normal Walk DMC score of 90 or 100. In another child, motor control could be playing a larger role, causing muscles to contract together at the wrong time, and their Walk DMC score could be 60 or 70. Orthopedic surgery in this latter case might cause more harm than good.
“When a child with cerebral palsy has a substantial impairment in selective motor control, the orthopedic surgeries may not be as successful,” said Jessica Rose, professor of Orthopaedic Surgery at the Lucile Salter Packard Children’s Hospital and the Stanford University Medical Center. “It might not be what’s causing the gait abnormality.”
The Walk DMC tool “would be the first objective assessment of muscle activation patterns while walking, and it is a real step forward,” said Rose, who was not part of the study. “It’s a very innovative application of statistics.”
One of the advantages of the new assessment tool is that it utilizes equipment already regularly in use in clinical settings, so it won’t require investments in new technology and can be easily adopted, said Steele, who directs the UW Human Ability & Engineering Lab.
The Walk DMC research was funded by the National Institute of Neurological Disorders and Stroke within the National Institutes of Health.
Steele and her colleagues at Gillette, which include Michael Schwartz, director of biomedical engineering research at Gillette Children’s Specialty Healthcare, and Adam Rozumalski, an engineer at Gillette Children’s Hospital, will be able continue their work thanks to a new $1.5 million NIH grant.
The plan is to test the Walk DMC metric as a predictive tool for who will benefit from surgeries, and help drive research in alternative treatments for children with more serious motor control challenges.
“We’re going to keep pushing it forward,” Steele said.
