May 2015

Dual-task gait: The potential influence of orthotic devices

5AFOcollage2-copyClinicians know walking while performing a secondary task can be particularly difficult for elderly patients or those with neuromuscular impairments. But new research suggests the use of orthotic devices may improve dual-task gait, which could significantly improve quality of life.

By Cary Groner

People are natural multitaskers. We can walk and chew gum, in fact. We swim and count strokes, sit and count breaths, eat and count calories. And how we talk: We gab while doing chores, gossip while jogging, yak while driving, whisper during movies. We discuss pension plans while piloting commercial airliners and overshoot our destinations by a hundred miles. Communication and related cognitive tasks are so important to personal happiness and social cohesion that we’ve evolved to integrate them into almost anything we do, especially while getting around.

Perhaps not surprisingly, research suggests that ambulation includes a cognitive component that involves allocating attention to environmental factors.1,2 Anyone who’s inadvertently chest-butted a parking meter while walking and talking with a comely companion knows how it feels when that attention is poorly distributed. It hurts.

But for some people—kids with neuromuscular disease, the elderly, or those recovering from stroke, for example—that type of hurt can become routine, because maintaining any sort of stable gait requires so much attention that secondary tasks become dangerous distractions. As a result, any strategy to help stabilize or improve gait could, theoretically, offer more than immediate biomechanical advantages; it might also normalize interpersonal interactions and make socializing easier.

For some patient populations, maintaining any sort of stable gait requires so much attentional focus that secondary tasks become dangerous distractions

Until recently, however, there was scant evidence to quantify the effects of a more stable gait on secondary tasks such as counting or conversation. But this February, a team of Chicago researchers presented a paper at the annual meeting of the American Academy of Orthotists & Prosthetists in New Orleans showing that ankle foot orthoses not only were associated with improved gait parameters in children with myelomeningocele (MMC, the most severe form of spina bifida), but also were associated with enhanced performance on a simultaneous counting task.3

The researchers recruited 18 kids aged between 7 and 13 years who had MMC, fit them with custom solid AFOs, then assessed them two weeks apart. On the first visit, the participants walked with shoes, but without AFOs, under two conditions: just walking, or walking while performing a counting task (the counting was also done as a single task to establish a baseline). On the second visit, the children repeated these tasks (the order was randomized) while wearing AFOs.

Photo courtesy of Insightful Products.

Photo courtesy of Insightful Products.

“We were really taking the first step in examining kids with spina bifida to see what happens to their performance in these dual tasks,” said Nikta Pirouz, CPO, who practices at the Anne & Robert H. Lurie Children’s Hospital of Chicago.

Pirouz and her coauthors told LER that they were interested in helping determine the extent to which AFOs might have more than a biomechanical effect.

“Can they facilitate more meaningful social relationships, better performance in school, quality of life issues we might not normally think about as orthotists or therapists?” Pirouz asked. “Our overall goal is to provide our patients with a more efficient gait, and there are many ways to do that—balance, stability, alignment, pain reduction. And, if you’re able to increase their gait efficiency, in theory you should see an improvement in a dual task while they’re walking with their device, as an indirect measure of that increase.”

The researchers reported that velocity and stride length increased significantly when participants wore the AFOs, both when walking and when the secondary task was added. But the AFOs
didn’t just affect gait; counting performance also significantly improved. Both response rates and rates of correct response got better, and dual-task counting performance approached single-task levels. The authors suggested that the increase was likely due to the AFOs reducing the attentional demands of walking, freeing up cognitive resources for other activities. Moreover, the children prioritized the counting task, preserving performance in that realm even when velocity suffered.

Pirouz’s coauthor, Tasos Karakostas, MPT, PhD, associate director of the Clinical Motion Analysis Center at the Rehabilitation Institute of Chicago, explained that the theory underlying the research has to do with attention, which is related to the brain’s executive function.

Photo courtesy of Össur Americas.

Photo courtesy of Össur Americas.

“There is more work to be done, but the data suggest that an AFO can have a cognitive effect on performance,” he said. “The AFO seems to be tapping the attentional component of the executive function, though that function involves the integration of a number of things.”

Despite the promising findings, Pirouz noted that interpreting the team’s results presents demands.

“The next step is for us to more fully understand the mechanism, how AFOs affect attention, if they really do,” she said. “There are so many different gait variables that it’s going to take time. For example, in our study we found that velocity increased with the use of AFOs, but that it was driven by cadence in the dual task and by stride length in the single task. Interpreting that is a challenge, but that’s the path we want to go down so we can better understand what’s going on.”

Stroke patients

Other researchers are conducting similar investigations. For example, scientists in Nova Scotia enrolled 21 individuals with poststroke hemiplegia and evaluated the effects of an AFO on dual-task gait (velocity, step length, swing time) as well as on a secondary counting task.4

The lead investigator, Kim Parker, MASc, a rehabilitation engineer with the Capital District Health Authority in Halifax, told LER that her concerns are similar to those that interested Pirouz and her colleagues, though in a different patient population.

“People who have foot drop after a stroke have to concentrate so they don’t trip,” Parker said. “We wanted to know what gets sacrificed in that [dual-task] situation; is it motor control, or the cognitive task, or both? We thought that if we introduced a dual task, we’d be able to show more measurable benefits of having an AFO.”

Parker said the data have not been fully assessed, but preliminary analysis indicates that AFO use was associated with improvement in the measured gait parameters under both single- and dual-task conditions. It didn’t significantly affect performance of the secondary task, however. She acknowledged, like Pirouz, that these results invite further inquiry.

Photo courtesy of Richie Brace.

Photo courtesy of Richie Brace.

“I was surprised that we didn’t pick up a difference in accuracy or reaction times [in the counting task],” she said. “I thought that, without the brace, their cognitive test would decline, but it didn’t, and I’m not sure why.”

A colleague of Parker’s who collaborated on the study, Gail Eskes, PhD, of Canada’s Dalhousie University in Halifax, emphasized that such results shouldn’t be considered an experimental failure.

“I wouldn’t take that as a negative,” she said. “I would interpret it that they were able to walk with an AFO and not be affected by the dual task.”

Eskes, a neuropsychologist, has investigated the nature of cognitive-motor interference in depth.

“We’re always struggling with whether anything we do in the lab is going to relate to the challenges patients have when they leave the hospital and go back to their daily lives,” she said. “When I first got involved with this study, my concern was whether dual tasking would make walking with an AFO harder. I think that if walking isn’t hurt by the dual task, then you’re doing really well; it suggests that there’s plenty of attention for both things, that you’re doing it fairly normally.”

Cerebral palsy

One explanation for such disparate results may be simply that the patient populations studied are so heterogeneous. What applies to individuals with spina bifida may not apply to those with poststroke hemiplegia. Researchers must contend with such variables in both experimental design and interpretation of results.

In conditions such as cerebral palsy (CP), for example, there isn’t yet any dual-task literature about AFOs and gait, but there are studies that look at dual tasking and postural control. In a 2008 paper published in the Archives of Physical Medicine and Rehabilitation,5 researchers at the University of Oregon in Eugene investigated the interference between a secondary task and a postural task in eight
children with CP aged between 10 and 14 years, versus typically developing children in two age ranges: 4 to 6 years (n = 5) and 7 to 12 years (n = 6). The postural task involved shifting from wide stance to a less-stable narrow stance; the cognitive component was a visual-memory task.

The authors found the children with CP were more physically unstable and had less executive attention capacity than the typically developing children for all conditions, though their performance was closer to that of the younger cohort. The kids with CP “had the least ability to allocate attentional resources to the processing of these two tasks, each with a large attentional load,” they wrote.

Photo courtesy of Allard USA.

Photo courtesy of Allard USA.

The paper’s lead author, Dinah Reilly, PT, PhD, was a physical therapist for 40 years before her recent retirement, and worked in the Boise, ID, school district for 25 of those years. She noted that kids with CP face unique challenges with dual tasking.

“There isn’t a pure quiet stance for a child with ataxia,” she said. “There’s a pendulum effect, a sway, and we noticed that, when you challenge them by putting their legs together, they sway even more. If you add a secondary task, both their postural control and the secondary task deteriorate, which indicates interference with both tasks. We didn’t see that with the other children.”

In her work as a physical therapist, Reilly modified her approach based on her research findings and applied the changes not only to postural control but to gait training.

“I decided that I needed to be quiet,” she said. “They were trying to process what I was saying and also trying to balance, so I tried not to confuse them with words. When they’re walking and you’re watching their gait, the minute they start talking, they either start to fall or they stop walking to talk to you, because they can’t do both.”

When Reilly subsequently trained staffers in the schools she worked in, she passed this methodology along, instructing them not to talk to children who were trying to walk.

“I told them to cut out anything distracting, because something that most of us take for granted isn’t automatic for these children,” she said.

Reilly told an anecdote about a boy with spastic CP who could walk with his walker if the story he was telling had been repeated often enough that it was automatic. But if she asked him questions, he had to stop walking to answer them.

“If he didn’t have support, if he started walking and tried to tell you a story, he just fell forward,” she said.

This can sometimes play out tragically when such children try to participate in physical education class or other exercise activities, Reilly pointed out.

“It breaks my heart, because they can’t screen out all the distractions, and it takes a lot more of their attention to walk, stand, do what’s asked of them,” she said. “People who work with these children need to understand that.”

When such children are fitted with AFOs, she continued, the devices may initially make their lives more difficult until they have had time to adjust to the changes.

“They may have an equinus gait, so you’re changing where they initially put their weight down, which changes the whole biomechanics of the body,” she said. “Some AFOs take away a child’s ability to balance.”

Photo courtesy of Ottobock.

Photo courtesy of Ottobock.

Reilly spoke of another young boy she knew who had ataxia.

“When he stood on a moving force plate, he had a normal sequence of postural control starting at the ankle and moving up to the hip; so his ankle grabbed, even though there was a pendulum effect from overreaction,” she said. “But, if [clinicians] put him in a solid AFO, he refused to stand because he couldn’t bring his toes up to prevent himself from going over backward. They thought they were giving him stability, but they took away his control.”

The timing of AFO prescription depends on the child, Reilly said.

“Ideally you’d decide based on a gait analysis, because otherwise you take away their ability to compensate,” Reilly said. “The easier you make it for these children, the more attention they’ll have for secondary tasks. Children just want to play; they don’t want to have to pay attention to their walking.”

Heterogeneity

Bryan Malas, CO, MHPE, director of orthotics/prosthetics at the Ann & Robert H. Lurie Children’s Hospital of Chicago and one of the coauthors of Nikta Pirouz’s paper, noted that the heterogeneity of patient populations affects decisions about AFOs, as well.

“When we’re dealing with kids with spina bifida, depending on the level of the lesion, certain muscle groups are completely compromised,” he said. “There’s no stability or integrity around the joint itself, so we have to create that stability, typically with a stiffer AFO design. Someone with little or no motor strength around the foot or ankle—postpolio would be another example—requires a design that provides greater stability to create a more functional gait pattern.”

On the other hand, children with neuromuscular conditions in which fatigue is a factor may do better with other approaches, Malas said.

“An AFO with graded motion or stiffness may make it easier for that person to recruit compensatory gait strategies that are helpful for maintaining balance,” he said. “Stiffer AFO designs may hamper those compensatory strategies, which are essential for balance in such cases.”

Elaine Owen, MSc, MCSP, a pediatric physical therapist at the Child Development Center in Bangor, North Wales, UK, agreed that different patient subroups require individual approaches.

“The children with the most difficulty may be those with dystonias and ataxias,” Owen said. “They already have involuntary movements that suddenly occur when they’re not expecting them, so in a way they’ve got three tasks going on: one is just walking, one is dealing with these sudden movements, and then there are the cognitive tasks they’re asked to perform. It’s a bit like us when we’re balancing on ice; we put so much effort into it that if someone distracts us, we’re going to lose what little control we had.”

Owen expressed interest in the study by Pirouz et al partly because of the complexity of the secondary task, which entailed counting backward.

“It’s difficult; it’s not something you’d normally do when you’re walking,” she said. “I wonder if they’d also done something more normal, like having a conversation about what you’re having for supper, that perhaps younger children could cope with that better. If you have a neurological impairment, any task is going to be harder when you’re walking.”

Pirouz and Karakostas noted that counting tasks are easier to quantify than conversation, which makes them better candidates for experimental contexts.

Photo courtesy of Kinetic Research.

Photo courtesy of Kinetic Research.

“I know right away if you did the task correctly, and it also allows me to target one type of cognitive function,” Pirouz said. “In a conversation, how and what am I measuring? Working memory? Logical function? It becomes much more muddled.”

Owen noted that, in extreme cases, children with CP, hydrocephalus, or related conditions can become so disoriented by distractions such as loud noises that they completely lose postural control.

“I worked with a child who had a head injury who suddenly fell over one day, and I asked him what had happened,” she said. “A motorbike had gone down the road; I hadn’t even noticed. Leaf blowers, sudden noises—for them, this is what it would be like if you or I were walking down the street and an explosion went off. You’d certainly change your gait, wouldn’t you? These children can’t be taught to automate their responses to spasticity, and they never get over that startle reaction. This tells us a bit about what can be automated with practice and what can’t.”

Owen sees merit on both sides of the debate about AFOs.

“They can make standing balance worse if they’re not designed and aligned properly,” she said. “But if they’re set optimally, they frequently make balance a lot better, so then if you’re doing something else, your balance will remain more stable. With dystonic children, for example, AFOs regulate their steps; it’s like the difference between walking on the floor and walking on a tightrope would be for us. We need feet that are stable but mobile, and we need alignments that produce stability and mobility. Sometimes it’s only by fixing the ankle that you can actually sort out the foot and the shank; it’s a complex area.”

Priorities

One aspect of the current research is that it sheds light on how those in different populations prioritize their attention. For example, in Pirouz’s study, participants gave priority to the secondary task, and she speculated that they may simply have been motivated to show off their capabilities to researchers.

Gail Eskes reported similar findings in her work with poststroke patients;6 others have shown that older patients, particularly those with impaired balance, have trouble flexibly allocating their attention between primary and secondary tasks.7,8

“I think it’s important for our profession to move in this direction,” said Bryan Malas. “Often we have patients who go to the gait lab, and the kinetics and kinematics are better with the use of an orthosis, but they tell us they still have to think about what they’re doing when they’re walking with an orthosis. We need to lean into that more—optimize the alignment or design of the orthosis—so they don’t have to focus on balance during walking but can redirect their attention to other aspects of daily living.”

Orthotic treatment that improves some elements of the kinetics and kinematics of walking, but decreases the patient’s stability, is not the optimal outcome, Malas added.

“In such cases, the situation should be revisited to determine if orthotic treatment can be further optimized,” he said.

Cary Groner is a freelance writer based in the San Francisco Bay Area.

REFERENCES
  1. Davis BH, Maclagan M, Karakostas T, et al. Watching what you say: walking and conversing in dementia: preliminary studies. Topics Geriatr Rehabil 2011;27(4):268-277.
  2. Karakostas T, Davis B, Hsiang S, et al. Dementia-specific gait profile: a computational approach using signal detection theory and introduction of an index to assess response to cognitive perturbations. J Comp Nonlinear Dynam 2012;8(2):021018.
  3. Pirouz N, Karakostas T, Malas B. Ankle foot orthoses for children with myelomeningocele: functional effects under a dual task paradigm. Presented at American Academy of Orthotists & Prosthetists 40th Annual Meeting & Scientific Symposium, New Orleans, February 2015.
  4. Parker K. Effects of an ankle-foot orthosis on gait while performing an attention demanding task. Clinicaltrials.gov Identifier: NCT0130839.
  5. Reilly DS, Woollacott MH, van Donkelaar P, Saavedra S. The interaction between executive attention and postural control in dual-task conditions: children with cerebral palsy. Arch Phys Med Rehabil 2008;89(5):834-842.
  6. Plummer P, Eskes G, Wallace S, et al. Cognitive-motor interference during functional mobility after stroke: state of the science and implications for future research. Arch Phys Med Rehabil 2013;94(12):2565-2574.
  7. Siu KC. Dual-task interference during obstacle clearance and healthy and balanced-impaired older adults. Aging Clin Exp Res 2008;20(4):349-354.
  8. Hawkes T, Siu KC, Silsupadol P, Woollacott M. Why does older adults’ balance become less stable when walking and performing a secondary task? Examination of attentional switching abilities. Gait Posture 2012;35(1):159-163.

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