Ankle foot orthoses can make a neuromuscular patient’s gait pattern more like that of an unaffected person, but the devices can also be associated with compensations of their own. And in some patients, a more ‘normal’ gait pattern is not necessarily going to be more functional.
by Cary Groner, Lower Extremity Review January 2011
When dealing with those who have neuromuscular disease or neurological injury, many practitioners soon discover that a gait pattern one patient finds acceptable may cause a different one immense frustration. The trick is in reconciling what the individual wants with what works biomechanically—but that’s easier said than done.
A variety of conditions such as post-stroke hemiplegia, spinal cord injury (SCI), muscular dystrophy, and cerebral palsy (CP) may create compensatory gait patterns in patients, and interventions such as physical therapy and bracing with ankle-foot orthoses (AFOs) often help normalize gait. But the prevalence of such compensations makes it crucial that clinicians clarify the effects of interventions in each individual patient, not least because AFOs may create their own compensation patterns that interact with those already present. And as noted above, clinicians and patients sometimes disagree about outcomes; for some, optimal ambulatory efficiency is the desired result, whereas certain patients want to look as normal as possible when they walk regardless of how fast they’re moving.
|Defining “normal” — or not|
|“Someone who’s suffered a stroke may be walking with an extensory synergy pattern—where the foot is plantarflexed and they’re having a tough time clearing it during swing phase—so they compensate with hip hiking and circumduction,” said Bryan Malas, CO, MHPE, director of orthotics/prosthetics at Children’s Memorial Hospital in Chicago. “I can put on an orthosis to take away the primary problem, but those patterns may continue out of habit, which is why gait retraining is important. I don’t want to create more compensation, but rather eliminate some of those motions when I deem that necessary.”
Even so, Malas acknowledged, “normality” is a relative term and must be balanced with a thorough assessment of the individual patient.
“We have to ask if the compensatory pattern is a benefit,” he said. “Normalizing the gait may improve or sustain function, but not always. If these compensatory patterns are allowed to persist, what will be the long-term effects? Will they ultimately lead to a decline in function or increased pain? If so, we need to start thinking about strategies for intervention.”
But in certain cases, Malas pointed out, interventions may cause more harm than good.
“As practitioners, we can get so focused on normal gait that we miss the real needs of the patient,” he said. “Normalizing the gait at the expense of decreasing function, balance, or the activities of daily living may make things more difficult. If normalizing the gait allows us to improve function, that’s a good thing. If it decreases function, we need to revisit what we’re doing with our treatment.”
For example, when Malas treats children with Duchenne’s muscular dystrophy, he commonly observes lateral trunk shifting due to weak hip abductors, as well as a significant posterior lean with increased lordosis as a result of weak hip extensors.
“That’s the compensatory pattern that allows them to sustain ambulation,” Malas explained. “If I put on an orthosis that takes away those compensatory motions, I may create instability because of the underlying muscle weakness, and that child may have a difficult time walking or even lose the ability to walk. If such children become nonambulatory, 80 to 100 percent of them will start to develop kyphoscoliosis and pulmonary decline. So clearly there’s a danger in trying to eliminate some of these trunk motions.”
Malas noted that similar compensations arise in patients with spina bifida and polio. Correct alignment is particularly important in such cases.
“A misaligned orthosis can create imbalance issues that force the patient to compensate in order to maintain an upright posture in standing or walking,” he said. “If a patient is fitted with an AFO and tells the clinician they feel more unsteady, some practitioners just tell them they’ll get used to it. We have to be very careful about that, because they may not.”
In a paper published last year in the Proceedings of the American Academy of Orthotists and Prosthetists, Malas noted that to determine how AFOs can best address issues of imbalance and functional decline, clinicians should consider factors that include patient expectations, effects on the body’s center of mass, fatigue, area of contact, proprioception, and preservation of balance outside of normalized ambulation.
|Recent papers have generally found AFOs effective for treating conditions such as hemiplegia, but there are aspects of the research worth noting.
For example, a 2007 study from Taiwan found that in 58 patients who’d had hemiparesis less than six months, the AFO improved maximal excursion toward the affected side, which correlated with an increase in step length on the non-affected side and an improvement in walking speed. An earlier study from the same researchers reported that in subjects with hemiparesis of less than six months’ duration, wearing an AFO was associated with improvements in several balance parameters including weight-bearing distribution while standing, body sway while standing on a soft surface, movement velocity in a stability test, excursion toward the affected side, and cadence. Interestingly, however, patients with hemiparesis for longer than six months showed only minimal improvement on the same measures when wearing an AFO.
A 2004 randomized trial in the Netherlands, moreover, found that an AFO’s effect on chronic stroke patients’ walking ability was not clinically relevant. On the other hand, a 2010 study found that an AFO was associated with improvements in both balance and ambulation in hemiparetic patients, though 61% of subjects found the AFO “unaesthetic.” 
One issue in determining the relevance of research is that disagreement persists among professionals about outcomes measures.
“It’s always been stated that achieving normal gait means achieving normal gait speed, and that’s how a lot of the measures are done,” said Nolan. “In our work, we’ve found that an AFO does seem to increase gait speed, but gait speed is not like ketchup; you don’t just order it. It’s made up of many different components of the walking mechanism, so until you isolate exactly where the increase is coming from, you can’t relate it back to the brace.”
Nolan and her colleagues have determined, in fact, that in most cases an increase in gait speed is associated with an AFO’s effect on deceleration.
“There are parts of the gait cycle where it speeds up and slows down, and the AFO creates a more efficient rollover in heel strike, a more efficient transfer of weight,” she said. “What looks like an increase in speed is actually a decrease in braking.”
Nevertheless, there are limitations to what the orthoses can do.
“AFOs limit propulsion because patients can’t use that efficient third rocker,” Nolan continued. “Push-off doesn’t improve with the brace, and in roughly half our sample it actually gets worse.”
Gait biomechanics come into play in other ways, as well, according to Douglas Richie.
“We’re looking more and more at variability in stride length, alignment, and cadence,” he said. “People argue whether variability is good or bad, but generally, when you see it reduced, gait is more steady and functional.”
Patients who speed up and slow down as they walk experience speed variability; those who spend more time on one foot than the other have stance-duration variability. Often, Richie said, variability issues result from deficits in motor control and sensory feedback; Parkinson’s patients are particularly vulnerable to such problems.
|If a patient dislikes the effect an orthosis has on her gait—whether in appearance, biomechanical efficiency, or sensory response—she’s less likely to wear it, of course. Practitioners should carefully assess reasons for noncompliance to determine the best strategy going forward.
“There’s a human element to the AFO,” said Nolan. “You have to put it on for it to work.”
Nolan has studied AFO usage patterns with a small accelerometer that monitors and records the wearer’s number of steps per time interval over extended periods. Nolan has her subjects wear the device on the healthy limb, then subsequently on the brace.
“My idea was to find out how much they were walking in the community, then how much they were walking with the brace,” she said. “It varied tremendously, based on the severity of the injury or stroke, and on how active they were.”
Not everyone wants to walk around with sensible shoes that accommodate an AFO, and this turns out to be an especially big issue with women, Nolan explained. Remember the study in which 61% of subjects found AFOs “unaesthetic”?
“Just because you’ve had a stroke, it doesn’t mean you’re no longer concerned about how people view you and how you look,” she said. “It’s vanity.”
Others, though, want to do everything possible to get better—and ironically, this may lead to noncompliance as well.
“Some people feel that by wearing an AFO, by getting that extra help, they’re impeding their chances of recovering and getting stronger,” Nolan said. “There hasn’t been enough research to show that, but the idea is that you’ll have a better recovery if you’re able to gain strength and range of motion, and use those things when you walk. We’re trying to get a picture of that; if you wear it more often, do you have better gains? But people who can’t make those gains have to wear the brace. It’s very individualized, because it depends on where the injury was and how it affects your lower limb.”
Safety is an issue with such patients, of course, and AFOs may help in that regard.
“I’m a big fan of AFOs in terms of safety,” Nolan said. “I think they help people with a foot-drop deficit, and they’re great for people who are not always that active, and who, for medical or other reasons, can’t get that range of motion and strength back.”
|Sensory feedback and strategies for recovery|
|The effect of AFOs on sensory feedback may be helpful or deleterious, depending on the condition of the patient.
“We’re just starting to appreciate the role AFOs can play in improving balance in compromised patients,” said Richie. “The devices stimulate cutaneous receptors and even mechanoreceptors in the joints, to theoretically facilitate balance and proprioception. But in patients who are already hypersensitive, this mechanism may work in reverse. Stroke patients are hypersensitive, and plastic in contact with the skin could cause compensation.”
Sensory feedback is crucial in neurobiological approaches to rehabilitation, particularly in spinal cord injury, according to Preeti Nair, PT, PhD, an associate professor in the department of physical therapy at Seton Hall University in South Orange, NJ.
Nair, who has written on the subject for LER, said that as research reveals more accurately the relationship between the spinal cord and the brain, clinicians must adjust their use of AFOs to reflect a more informed and comprehensive approach to rehabilitation.
“For a long time, we thought that someone with a neurological injury would not be able to return to normal functioning,” Nair said. “We’ve thought of the nervous system in a top-down way; the brain is the primary center and the spinal cord is just a channel that communicates sensory information to the periphery. But the spinal cord also processes information from the periphery independently; it has little centers that regulate sensory information and provide feedback. It’s a kind of pattern generator that uses peripheral information to decide on the next sequence of action. If we can tap into that circuitry and retrain it, we may be able to think about recovering the ability to walk versus compensation.”
According to Nair, some of the sensory information has to do with mechanoreceptors that sense loading and unloading, joint position, and the like.
“We don’t evaluate well enough how proprioception affects movement,” she continued. “We don’t know how sensory information is getting processed when somebody is actually in the dynamic task of walking. If somebody is going to use an orthosis to walk, how is that sensory information changing? It’s important in order for them to process the next step, so I think it’s crucial.”
One implication of Nair’s research is that practitioners may need to assess more carefully when, in the rehabilitation process, AFOs are introduced.
“Usually, the patient comes in and the clinician says, ‘Okay, I see this particular deformity, this gait pattern. So here: you’re going to start walking with an AFO.’ I think that approach needs to change. If we can maximize a patient’s effort and minimize the use of the orthosis, that might be useful,” she said.
In the locomotor training that takes place in Nair’s lab, patients are supported by a harness as they walk on a treadmill.
“It’s important to give motion-related sensory input to the spinal cord so it can relearn a normal stepping pattern,” she said.
The aim is to progressively retrain the ability to step rather than substitute for impaired stepping. Patients wear an AFO for part of the training, but ideally they are weaned from it over time.
“We’re trying to translate our ideas for independent mobility on the treadmill to walking over ground, in the community,” Nair explained. “We may not want to look at orthotics as the first line of treatment anymore. If somebody brings me a patient, I want to do a complete kinematic and kinetic profile—look at the EMG, at joint range, at the forces they’re producing when they walk. Then I’ll decide what kind of orthotic device is good for them.”
Douglas Richie—despite having invented the Richie brace—agrees that as more information becomes available, clinicians need to reevaluate their approach.
“I don’t think you should rely on an AFO to restore gait or timing or speed,” he said. “I’m impressed more and more by the ability of rehab techniques to supersede the AFO and ultimately restore normal gait patterns, and it’s arguable that the AFO may actually impede that process.”
Richie said that regardless of how early in the process an AFO is prescribed, the practitioner must keep careful track of the patient’s improvement and modify the device accordingly.
“You can’t get into the mind-set that there’s going to be one device for the rest of their life,” he said. “Through therapy, the patient may achieve increased muscular control or range of motion that allows them to move into a different device—or none at all.”
|Cary Groner is a freelance writer based in the San Francisco Bay Area.|
Source Lower Extremity Review