AFO tuning: Balancing function and satisfaction

Tuning of ankle foot orthoses (AFOs) and AFO footwear combinations can significantly improve gait in patients with neuromuscular impairments. Even so, some patients still prefer their untuned devices, which has led researchers and clinicians to re-examine their approach to intervention.

SureStep birthday party.

By Cary Groner, Lower Extremity Review August 2014

As researchers and clinicians have continued to refine the tuning of ankle foot orthoses (AFOs) and AFO-footwear combinations, recent findings suggest an occasional disconnect between biomechanical results and patient satisfaction.

The research is still preliminary, and the extent to which its results are anomalous, or may instead affect future tuning protocols, remains to be seen. Nevertheless, experts have taken notice, and deeper inspection of the phenomenon is already leading to new revelations about the effect of tuning on the whole patient, particularly his or her comfort levels and happiness.

Consider a small study presented at the annual meeting of the American Academy of Orthotists and Prosthetists (AAOP) earlier this year.^[1] Clinicians from the Rehabilitation Institute of Chicago (RIC) examined the effects of tuning AFOs on dynamic balance in six patients (one of whom subsequently dropped out) with hemiparesis following a stroke, all of whom had worn untuned AFOs since their rehabilitation began an average of six months earlier.

Although the tuned AFOs were associated with stable balance scores and less knee hyperextension than the untuned devices, only one of the five patients who completed the study preferred the tuned AFO to the existing one.

SureStep birthday party

Lead author Katie Johnson, MS, CPO, described the process to LER.

“Initially, we did a full evaluation to assess patients’ range of motion and muscle strength,” said Johnson, who has since moved from RIC to Mary Free Bed Rehabilitation Hospital in Grand Rapids, MI. “We wanted to create the AFO, with shoe modifications, to get what we wanted from gait—a nice rollover with a good entrance to and exit from stance phase, with ten to twelve degrees of shank-to-vertical angle at midstance. We had subjects walk in their original AFO, so we had a baseline for that and barefoot walking, then fit them with the new AFO, tuned them, and videotaped them then and a month later.”

Although, as noted, the tuned AFOs offered some biomechanical improvements to gait—the patients even saw them on video—their confidence in their balance capabilities decreased.

“I think there was such a big difference between the original and the tuned AFOs, we were pushing them outside of their comfort zone,” Johnson acknowledged.

For Donald McGovern, CPO, who also practices at RIC (he had worked with Johnson previously but was not involved in this study), the research raised interesting questions about the best way to approach stroke rehab.

“This suggests that the motor pattern a person gets into, when they first get up after a stroke, is what they’ll continue to be comfortable with—whether it’s a good pattern or a bad one,” McGovern said. “Katie found that tuning can definitely improve ambulation in individuals, but if a patient has already established a motor pattern and they’re not comfortable changing it, they’re going to go back to what they’re used to.”

Another recent study suggests the importance of the first intervention. This June, researchers in Scotland published research concluding that custom-tuned AFOs, which controlled shank and ankle in eight early stroke patients, contributed to significant improvements in walking speed, step length, and cadence, versus walking with shoes only.^[2] The study didn’t compare tuned AFOs to untuned ones, so it’s difficult to extrapolate conclusions in that regard, but it got the attention of other clinicians, including McGovern.

“It indicates that, if we can get people up in the tuned AFO sooner, we could probably have much better results,” he said.

Elaine Owen, MSc, MCSP, a pediatric physical therapist at the Child Development Center in Bangor, North Wales, UK, attended Johnson’s AAOP presentation. She was particularly struck by the fact that the one study participant who preferred the tuned AFO had complained of extreme pain related to knee hyperextension in the untuned model. This made perfect sense to her.

“He was willing to tolerate a big change because it got rid of his pain,” Owen said. “When you tune an AFO to make the gait more normal, from heel strike until the toes are flat on the floor, you have to do knee flexion in loading stance—and to do that, you have to have strong quadriceps. If the subjects had been walking on hyperextended knees for years, they probably had very weak quads. With a tuned AFO, they’ll worry that they’ll collapse. Ideally, you’d improve the alignment and strengthen the quad gradually, to let them get acclimatized. You also want to do motor learning, do things in tiny increments until you get where you want while allowing them to learn a different walking pattern that feels normal to them again.”

Katie Johnson agreed, noting that patients needed to relearn how to walk, not only after the stroke, but also after an intervention with an untuned AFO.

“If they’re already used to that, do we start them out slowly, then build them up to the optimal angle?” she asked. “Do we need to get physical therapy involved? Can we begin this right away, so they don’t get into that hyperextension pattern? There are a lot of factors, and I’d love to keep going with this research, because we do see kinematic improvement.”

Another small study presented at the AAOP meeting reported similar conclusions. In that case, researchers from Northwestern University in Evanston, IL, found that although two children with cerebral palsy experienced improved kinematic and balance functions with a tuned AFO, only one was satisfied with it.^[3]

“It’s fair to say that for [the unsatisfied] child, there was a disconnect between the biomechanical and functional improvements,” said lead author Stefania Fatone, PhD, BPO (Hons), a research associate professor in physical medicine and rehabilitation at Northwestern. “It’s possible to be less than fully satisfied with some aspects of an orthosis such as fit, comfort, freedom from skin abrasions, and pain, even if it provides improved function in terms of its biomechanical aspects.”

What is tuning, anyway?

According to Elaine Owen, tuning an AFO typically involves assessing and adjusting shank and thigh kinematics so that during stride the shank passes through vertical and reaches an incline (often estimated at 10°-12°) at midstance. This contributes to stability; facilitates ballistic movement of the thigh, pelvis, and trunk; affects these and head kinematics; facilitates ground reaction force alignment relative to the knee and hip; and may contribute to energy conservation.^[4] A properly tuned AFO also contributes to proper rocker function.^[4]

Owen stresses, however, that despite the essential attention to detail, the process of tuning an AFO is not a purely mechanical one.

“The definition of tuning is to adjust for optimal performance,” she told LER. “Whether it is a violin or a car or an AFO, you are tuning it for the activity it has to perform. Some people think this is just static alignment; in the case of an AFO-footwear combination, that means adjusting the shank-to-vertical angle [SVA]. That is not tuning, and I have a bee in my bonnet about this.”

Tuning isn’t just about aiming for an SVA of 10°-12°, she emphasized, noting that for some patients the correct angle might turn out to be 9°-10°, whereas for others it could be 15°-16°.

“You’re not trying to get a certain preconceived incline; you’re looking at all the kinetics and kinematics to get it right for that patient,” she said.

Because the AFO-footwear combination (AFO-FC) is so often critical to correct tuning, Owen defined it separately in a paper ^[5] published this year: “The process whereby fine adjustments are made to the design and alignment of the AFO-FC in order to optimise its performance during a particular activity such as sitting, standing, transferring, stepping, walking running, climbing stairs.”

Moreover, she emphasizes, in both her interviews and her writing, the importance of a gradual approach. For example, in a case study published in Prosthetics and Orthotics International in 2010, she and her coauthors described the step-by-step tuning process for a 61-year-old woman with poststroke hemiplegia and pain associated with midstance knee hyperextension while using a custom polypropylene AFO that had not been tuned.^[6] The AFO-FC was incrementally modified over several weeks to optimize knee kinetics and kinematics and adjust ground reaction forces.

“Pain was her main issue, and it kept her from walking for weeks on end,” Owen explained. “Once we tuned her AFO, it kept her knee from hyperextending, which took away the pain and swelling so she could keep walking. She said it gave her her life back. We not only changed her gait, we alleviated her pain and allowed her to be active and do the things she wanted to do.”

Younger patients

“In cerebral palsy, or spina bifida syndromes, if you have neurological or genetic or muscle-weakness problems, and on top of this, skeletal structures that can’t take those abnormalities, the feet may deform terribly and need surgery,” she said. “In that situation, one of the main purposes of an AFO is to minimize the deformities that occur as part of the natural history of the condition. You hope that by age sixteen, when they’re fully grown, you’ll have had the least surgical interventions possible.”

This, like so many aspects of AFO tuning, involves the necessary wisdom of compromise.

“While you’re trying to teach them to move as normally as possible, you’re also trying to allow them to do the activities they want to do—running, jumping, bouncing on the trampoline. So what AFO design and frequency of use will give them good body structures and functions, but also allow them to do their activities? Those decisions are different for each child, and you have to decide what you’re trying to achieve,” Owen said. “Often what’s most important to these children is growing up with good mental health, not depressed about their disability. Ideally, you can get a good balance.”

As an example, Owen noted the problems associated with trying to get a child with Duchenne muscular dystrophy to walk more “normally,” despite the fact that this could compromise the child’s ability to get around due to the gait compensations they typically develop as a result of the disease.

“Why would you put something on a Duchenne’s child if they don’t function better?” she asked. “That’s madness. You want to tune the AFO so they do better; you want to increase their performance. You need to decide what you’re trying to achieve and then figure out how to get there. The AFO is a therapeutic device.”

Because fixed AFOs are often prescribed for such children, this year Owen published a paper containing an algorithm for determining whether a dorsiflexion-free AFO-FC is appropriate, versus a fixed design.^[5]

Kristie Bjornson, PT, PhD, a pediatric physical therapist at the Seattle Children’s Research Institute and an associate professor of pediatrics at the University of Washington in Seattle, praised Owens’s algorithm.

“I tend to think our orthotics practices have been eminence-based rather than evidence-based, meaning that a master clinician we respect does it a certain way, then teaches their students, who go on to do it the same way for the next twenty years,” Bjornson said. “It’s one reason orthotic practices are so different in different parts of the country, but it’s also a reason that what we’ve been doing isn’t working very well. Elaine’s algorithms are a light-year advance, because orthotic prescription is an individualized intervention, and having that decision tree available supports consistency of AFO prescription as you see different clinical impairments and walking pathologies.”

Bjornson’s research focuses partly on how well clinical interventions translate into the daily activities of her patients, many of whom have cerebral palsy. She described the tuning process for one of her patients, a boy she began to treat when he was 4 years old, and who is now 6.

“He had an equinus gait pattern, very flexible hips, tight hamstrings, limited passive range of motion at the ankle, and gross motor function classification of level 2,” she said. “He was wearing a solid ankle AFO and walking on his toes in these braces with his knees bent, in a jump gait pattern. We changed his AFO prescription, wedged him [under the heel] to incline his shank-to-vertical angle and help static standing and stability in midstance, then added a point-loading rocker at eighty-five percent of his shoe length to help time heel-off. Then we put him in a gait training program.”

The result of the AFO tuning was that the boy’s static standing balance improved significantly, he could stand still and hold things more easily, his stride length and walking speed increased, and his amount of community walking improved, according to Bjornson. The boy’s optimal SVA was 8°-10°; other patients of Bjornson’s have had SVAs as low as 4° and as high as 15°. (The data will be included in a paper she and her colleagues are now preparing.)

Bryan Malas, CO, MHPE, agrees with this focus on the individual patient.

“I can’t emphasize enough how important it is to identify the desired outcome for the patient, prior to tuning,” said Malas, who is director of orthotics and prosthetics at Lurie Children’s Hospital in Chicago. “Tuning is a means to an end.”

In his own practice, Malas pays close attention to the sequence of events in an approach similar to that of Bjornson.

“First, we need to determine the patient’s range of motion and accommodate it appropriately,” he said. “Once we’ve done that, we can begin to address kinematics, look at the relationship of the AFO in the shoe relative to the heel-sole differential. Do we need to add wedging to change that? Then you’re looking at the relationship between the shank and the forefoot distally, and the relationship between the shank, the thigh, the hip, and the trunk proximally. In the end, this all has to be tailored to individual patients and their needs—again, to what you’re trying to accomplish. I need to make sure my expectations are in line with the patient’s.”

Malas thinks, also, that clinicians too often overlook the vital role of the shoe in AFO tuning.

“If you have a properly designed AFO but inappropriate footwear, it can completely derail you from optimizing the patient’s gait and achieving your desired outcomes,” he said. “If you take away motion [with an AFO], you need to give that motion back; so for example if we’re using a solid AFO, then we need to think about what to do with the shoe. Do we need a custom heel, or a rocker at the front? You need to consider those things without compromising stability or balance.”

More severe gait deviations complicate the process, for example, in the case of a patient who has a severely crouched gait pattern with knee flexion contractures.

“In a case like that, you’re limited in what the AFO can accomplish, and if you don’t get the alignment right, it may make the crouching worse,” Malas said. “Other modalities may be necessary to gain range of motion first; then you’re in a better position to determine what the AFO can do.”

Like Elaine Owen, Malas draws a distinction between normal and optimal gait.

“If normalization creates an optimal gait pattern, that’s great, but in some cases trying to achieve normal gait will just create more instability,” he explained. “If we try to create a normal gait in a child with, say, Duchenne’s, they wouldn’t be able to walk.”

Getting clinicians on board

Given how vital such clinicians consider AFO tuning, it would seem that the practice would be universal. Far from it, as it turns out. This may partly reflect the occasional disconnect already noted between biomechanical outcomes and patient satisfaction. But it may also be about ignorance.

For example, a study published earlier this year reported that very few clinicians in the UK even responded to a questionnaire about tuning, and that, of those who did reply, barely half use the AFO-FC tuning as standard clinical practice.^[7] The most common factors cited as barriers to tuning were a lack of access to 3D gait analysis equipment (37%) and a lack of time (27%). As it happens, 3D gait analysis isn’t necessary to tune an AFO.

One of the study’s authors, Nachi Chockalingam, PhD, a professor of clinical biomechanics at Staffordshire University in Stoke-on-Trent, England, told LER that, even among those clinicians who claimed to tune AFOs, there were problems.

“When we looked in detail and asked further questions, it was obvious that they didn’t understand some of the basic principles of tuning,” he said.

The results have spurred Chockalingam and his colleagues to study tuning protocols further. In 2012, they published a review of the research on the effects of tuned AFO-FCs on gait in children with cerebral palsy, and reported that although the results suggested efficacy, most studies were poorly designed and powered.^[8]

Even so, it’s worth paying attention to some of the published data. For example, a 2009 study on five patients with cerebral palsy found that tuning the AFO-FC significantly reduced knee hyperextension during stance and improved the SVA angle.^[9] And a 2014 study on eight patients with cerebral palsy reported that tuning the AFO-FC showed benefits, including a significant reduction in peak knee extension and knee range of motion during gait.^[10]

Given such promising if small-scale studies, and the low levels of tuning clinicians report, Chockalingam and his colleagues hope to improve participation by developing additional protocols that involve minimal equipment.

A team approach and understanding of tuning is essential for progress, according to Don McGovern.

“If you get the physical therapist, the orthotist, the parents, and the child all working together, it can be quite successful,” McGovern said.

Bryan Malas noted that success may sometimes be demonstrated in subtle but unmistakable ways. Once in the clinic, he put a patient into an untuned AFO; the boy, who had been reading while standing, immediately stopped reading his book because he was unstable and had to pay attention to his balance. After the AFO was tuned, he started reading again.

“There’s a bigger piece here,” Malas said. “As clinicians, we get so focused on kinetics and kinematics that we can lose sight of what’s most important to the patients. They just want to feel stable without having to think about it, so they can live their lives.”

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

Source Lower Extremity Review

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