Studies suggest that ankle foot orthoses can improve balance in some individuals, so it might seem logical that they would also help prevent falls. But the medical literature has yet to reveal a direct connection between AFOs and falls risk, and as a result the issue has become a magnet for debate.
By Cary Groner, Lower Extremity Review August 2012
As the complex processes by which people achieve and maintain balance become better understood, researchers and clinicians are increasingly focusing on ways to improve balance in athletes, the elderly, and patients with neuromuscular deficits that affect postural control and movement. Preventing falls is one clear application of such research, but the relationship between balance control and fall risk, though apparently intuitive, depends partly on the population being studied and can be difficult to quantify. Ankle foot orthoses (AFOs) are often prescribed for patients with conditions that affect balance, but the extent to which the devices may raise or lower the risk of falls depends on a number of variables and remains a matter of debate.
Falling is a serious problem in the elderly and those with neuromuscular problems. In 2007, according to the National Safety Council, falls resulted in the deaths of more than 21,700 Americans. Falls are the leading cause of injury-related death in those older than 73 years, and the second-leading cause in those aged 60 to 72 years.
Among patients in the acute phase of inpatient stroke recovery, up to 47% fall, and 70% fall in the first year after stroke. In patients recovering from acquired brain injury, 54% reported a fall in the previous six months. Seventy-five percent of those with incomplete spinal cord injury have at least one fall in the course of a year, and 18% of those experience a fracture as a result. In post-polio patients, 64% reported a fall during the year, and 35% had a fracture. In adults with peripheral neuropathy, 65% fell during the previous year.
To understand whether AFOs may prove useful in addressing these problems, it’s important to understand how people maintain their balance.
A useful definition of balance was provided in a systematic review of AFOs and balance published in 2010 in the Journal of Prosthetics & Orthotics (JPO); namely, that it is a complex skill necessary to maintain the body’s center of gravity within the base of support while stationary (static balance) and to control the center of mass (COM) in dynamic situations such as walking or when experiencing a destabilizing event (dynamic balance). Maintaining balance involves cognitive, motor, cerebellar, vestibular, and proprioceptive systems, the relative contributions of which depend on age and pathology. A crucial biomechanical factor is the patient’s ability to maintain the COM within the base of support, and limitations in sensory input, muscle strength, or joint range of motion affect this ability.
So how do AFOs fit in? It turns out to be a good question.
“In this article we looked at how ankle-foot orthoses affect balance,” said author Nerrolyn Ramstrand, PhD, BP&O (Hons), an associate professor of prosthetics and orthotics at Jonkoping University in Sweden. “What seems to be missing in the literature is the link between balance and other measures of function. We can potentially say that yes, an orthosis can influence balance, but how does that carry over into fall risk or function in everyday life?”
This question—a critical one—has been the source of significant research and debate. The entire issue of JPO in which Ramstrand’s article appeared focused exclusively on the effect of AFOs on balance. At the Boston conference of the American Orthotic & Prosthetic Association (AOPA) scheduled for this September, several presentations will examine the effect of AFOs on balance. Moreover, marketing claims that at least one AFO reduces the risk of falls in elderly patients have provoked professional scrutiny and led to published challenges.
|Pros and cons|
In the introduction to the special JPO issue noted above, Phil Stevens, MEd, CPO, who works for Hanger Prosthetics & Orthotics in Salt Lake City and will present at AOPA in Boston, noted the ankle strategy—the muscle-tendon stretch reflex that sends feedback to the central nervous system about sway and leads to muscle firing to correct alignment—is crucial to balance. By crossing the ankle joint and affecting joint kinematics, kinetics, and proprioceptive inputs, he wrote, AFOs may have positive or negative effects on balance in a variety of activities.
“In the best-case scenarios, AFOs can compensate for existing balance deficits, reducing fall risks, improving confidence, and facilitating greater activity and participation,” Stevens noted in the text. “However, AFOs also have the potential to further compromise balance with the undesirable sequelae of possible falls and related injury, an increased fear of falling, and subsequent activity restriction.”
Specific AFO design characteristics may play a role, Ramstrand said.
“If you have some form of ankle weakness, a rigid AFO might help you in static balance,” Ramstrand said. “But we found that they can compromise dynamic balance, because then you use your ankles to control your center of gravity. In dynamic activities, we found that a leaf-spring orthosis, which is much more flexible, seems to be a little better.”
Ramstrand’s review reported that sports AFOs had mixed effects on balance in healthy populations: six articles found no effect, two reported negative effects, and five found positive effects.
In subjects with neuromuscular pathologies including cerebral palsy (CP), poststroke hemiplegia, multiple sclerosis (MS), and peripheral neuropathy (collectively described as studies of “ambulatory orthoses”), results were similarly disparate. For example, one study in children with CP reported that rigid AFOs caused a delay in recruitment of the gastrocs and an inability to use the ankle strategy for balance recovery—a problem not seen when the subjects were fitted with non-rigid AFOs or none at all. Another study in MS patients reported that a rigid AFO positively influenced static balance but negatively affected dynamic balance, which was improved by nonrigid AFOs.
As noted by Ramstrand, leaf-spring AFOs fared the best in the review. Five articles studied them in poststroke hemiplegia and one looked at the devices in peripheral neuropathy; all found generally positive effects on balance and sensory organization. Similarly, supramalleolar orthoses were judged beneficial for enhancing balance in children with spastic CP.
Ramstrand told LER that although drawing a correlation between balance measures and fall risk was difficult, certain tests—e.g., the Timed Up and Go test—did appear to hold more potential in that regard.
|Trends and fatigue|
“One thing that came out of the Ramstrand review is that most of the AFO studies that have been done are not reproducible,” said Bryan Malas, MHPE, CO, director of the Orthotics-Prosthetics Department at the Ann & Robert H. Lurie Children’s Hospital of Chicago, and an instructor of physical medicine and rehabilitation at Northwestern University’s Feinberg School of Medicine. “The number of subjects is usually very small, and we can really only say, ‘Here are trends we saw.’ To get a handle on balance, postural control, and the risk for falling, we need studies that are more reproducible and that address the cognitive and attention piece of this, which we’ve neglected for a long time.”
Malas, who will also present at the September AOPA conference, contributed a paper on clinical perspective to the special issue of JPO. He noted that the variables contributing to decisions about AFO design and fabrication—materials, footplate length and stiffness, ankle configuration, and footwear considerations—affect the device’s ability to influence balance and stability.
He also outlined the important and often underrated influence of fatigue on assessments of balance control. Dorsiflexor fatigue increases the risk of failed swing phase clearance, increasing fall risk, and may also compromise the ankle strategy during static reaching. Plantar flexor fatigue may permit increasing crouch during gait and lead to knee buckling. Fatigue of the knee and hip extensors increases the risk of anterior knee instability and associated falls. Finally, hip flexor fatigue also affects swing phase clearance, increasing the risk of trips and falls.
Existing studies may have underestimated the effects of AFOs on balance by failing to account for fatigue, Malas wrote.
“It all comes down to time assessment,” he told LER. “If I have someone walk for ten seconds, but fatigue doesn’t set in for two minutes, am I getting a true picture of how that person is walking? I’m not, and I end up making decisions that aren’t relevant when the patient is fatigued.”
He provided an example from his own practice, in which a child came in and walked back and forth a few times.
“There were some problems with clearing the foot during swing phase, and based on that assessment, I might have given the child a posterior leaf-spring AFO,” Malas said. “But then the mom said, ‘This isn’t really how my child walks. After four blocks, my child will be in a full-crouched gait.’ A posterior leaf spring isn’t going to effectively manage that; the child needed solid AFOs. So if you stop too soon and only have the person walk a few steps, you may not get a true picture of the situation, and the treatment may not be appropriate.”
Another of the JPO papers, this one by Aruin and Rao, was a study that looked at the effect of AFOs on proprioception—the transmission of information provided by receptors in the muscles, tendons, and joint capsules about muscle length, contractile speed, muscle tension, and joint position. Loss of lower limb proprioception particularly afflicts the elderly and those with neuropathy and has been shown to contribute to instability and falls.[10-12]
Ramstrand, in her review, pointed out that previous research failing to show proprioceptive effects of AFOs had been conducted in healthy individuals, and suggested that AFOs would be unlikely to have proprioceptive effects in those with normal neuromuscular function.
The authors of the JPO article on proprioception, however, noted that, in patients with diabetic peripheral neuropathy, studies demonstrated that AFOs improved automatic postural responses, but that this could have occurred due to either auxiliary sensory cues or to the mechanical support the AFOs provided.[13,14] In their JPO paper, they studied 12 subjects fitted with AFOs designed to provide auxiliary sensory cues to the lower limbs without stabilizing the ankle joints.
The researchers reported that, in patients with sensation loss due to peripheral neuropathy, the devices let sensory information bypass the disrupted pathways in the lower legs, substituted for the loss of proprioceptive feedback, and helped subjects generate faster and more sensitive postural responses while standing. They emphasized, however, that it appeared to be critical that the AFO be tall enough to reach the upper part of the lower leg in order to have this effect.
The discussion in the clinical community becomes more heated when it comes to the role AFOs may play in preventing falls in non-neurologically impaired elderly patients. As noted earlier, older people have a high fall risk. It’s not that they necessarily trip or slip any more than younger patients, however—it’s that they don’t recover as well due to slower reaction time, weaker muscles, and comorbidities such as vestibular dysfunction, poor vision, and proprioceptive loss.[15,16]
Existing research indicates that lower limb reaction time discriminates between single and multiple fallers older than 65 years. And a recent meta-analysis from Australia concluded that exercise is the most effective single intervention to prevent falls in the elderly.
But might AFOs play a role? Jonathan Moore, DPM, director of Cumberland Foot Health Solutions in Somerset, KY, and an adjunct faculty member at the Ohio College of Podiatric Medicine in Independence, thinks so. Moore has developed a leaf-spring AFO called the Moore Balance Brace (MBB) that, according to claims in a video on his website, will reduce the risk of falls, improve proprioception, and stabilize the ankle in older patients. (The MBB is advertised in LER).
Moore promotes the MBB as one component of an overall fall prevention program, which includes assessments by the podiatrist as well as educational materials about exercise, physical and occupational therapy, and appropriate referrals. Clinical indications for the brace listed on the website include difficulty walking, fall risk, vestibular disorder, chronic ankle instability, arthritic ankle, stroke imbalance/foot drop, and diabetic peripheral neuropathy. Moore, however, emphasizes the brace’s use in elderly patients, and his claims in this context have raised eyebrows among some other clinicians.
“I’ve developed an approach to help your senior patients at risk for falling and to avoid injury,” Moore states on the website video. “The Moore Balance Brace was specifically designed to be a tool that the podiatric physician can use to help reduce the risk of falling by stabilizing the ankle. The MBB is a device that is lightweight, it is a device that has been shown in studies to vastly improve proprioception, but most importantly, the MBB will improve postural control and thereby reduce the risk of falling.”
Moore declined to be interviewed by LER, but he did respond to questions via email. He said that his older patients found existing AFOs too heavy and restricting, so he developed the MBB to be lighter and easier to put on and take off. The MBB has a thermoplastic inner shell with posterior leaf spring trim lines.
“These devices are light and flexible,” he wrote. “They are stable enough for most adults, but they do not limit normal sagittal plane motion.”
In a document available on the MBB web site, Moore states, “[A] balance AFO can lead to sensory reorganization for postural control as a function of the neuromuscular constraints acting on the patient’s foot and ankle. An AFO can provide significant improvement in postural control and, in aging, help to reduce the risk of falling and its potential for injury.”
Chad Lairamore, PT, PhD, an assistant professor of physical therapy at the University of Central Arkansas in Conway, acknowledged that it isn’t so far-fetched to link stability with the risk of falling.
“You’d have to have a very limited definition of postural control not to relate it to fall risk,” he said. “If you had no postural control, you’d never fall, because you’d never get up.” (Lairamore was speaking generally, not in response to Moore’s assertions.)
It is unclear from existing research, however, whether in neurologically normal patients—even older ones—AFOs provide the type of proprioceptive enhancement or gait stabilization that would reduce the risk and incidence of falls.
“I don’t know that I could make a statement like that,” said Bryan Malas, when read the section from the document above. “There are so many variables mentioned in there; you could pull one of those out and do research for years.”
The Australian researcher Hylton Menz, PhD, has studied falls in the elderly extensively. Menz is a senior research fellow and head of the Lower Extremity and Gait Studies program at La Trobe University in Melbourne, Australia, as well as editor in chief of the Journal of Foot and Ankle Research.
“There’s currently no evidence from randomized controlled trials to support the claim that [ankle foot orthoses], when used in isolation, can prevent falls,” Menz told LER. “Our group recently conducted the first-ever trial of a podiatry intervention, which reduced the rate of falls by 36 percent; however, this involved a foot-and-ankle exercise program, regular podiatry care, and a footwear subsidy in addition to prefabricated foot orthoses.”
Douglas Richie, DPM, designer of the Richie Brace, questions the connection between postural control and falls prevention in the neurologically normal elderly. (Richie Brace is an advertiser in LER).
“Falls are multifactorial, and any device that limits motion of the ankle joint will compromise the most important sensor mechanism for balance and postural control—the muscle spindles and tendon stretch receptors that are part of the somatosensory system that gives essential feedback for balance and postural control to the central nervous system,” said Richie, owner of Seal Beach Podiatry in Seal Beach, CA, and associate clinical professor in the Department of Applied Biomechanics at the California School of Podiatric Medicine in Oakland. “I just don’t know that anyone has predicted that in [a neurologically normal] elderly patient, if you improve their postural control you’ll prevent falling. For that matter, when your foot is locked in a plastic shell, you may not recover from a trip as well. The goal of AFO therapy is to treat a weakness or deformity and improve gait stability, to treat a specific musculoskeletal condition or neurologic deficit.”
|Revisiting the literature|
Moore declined LER’s request to respond to Richie’s previously published criticisms.5 He did, however, provide a number of citations from the medical literature on which his claims about the MBB are based.[22–26,31–33]
Regarding proprioception, he wrote, “It has been demonstrated in multiple studies that proprioception can be enhanced by an AFO through somatosensory feedback created through contact with the skin.”
One citation provided by Moore reported that “the AFO allowed the subjects to limit the postural perturbation induced by a localized fatigue of the ankle muscles during bipedal quiet standing.”  The authors speculated that ankle proprioception, altered by fatigue, might have been enhanced through increased cutaneous feedback provided by the AFO. Another citation Moore provided was the JPO article by Aruin, which was conducted in subjects with peripheral neuropathy and involved a specially designed AFO.9
Moore also cited studies[23-26] showing that contact with a stable external surface positively influenced apparent body orientation and wrote, “Thus, AFOs in addition to correcting the patient’s foot placement during locomotion, can also be expected to improve the maintenance of balance during quiet stance or dynamic perturbation.” The studies in question, however, report on subjects who stood touching a wall or a bar with a fingertip.
It’s a complex issue, Hylton Menz noted.
“Although there is good evidence that externally applied devices can enhance postural stability by providing additional sensory feedback, this needs to be balanced against the possibility of restricting motion in the ankle-subtalar joint complex, which could be detrimental to balance,” he said. “Our research has previously shown that even imperceptible tactile stimuli applied to the leg can reduce postural sway in young, old, and neuropathic subjects. However, we have also shown that reduced ankle joint motion is associated with impaired balance and an increased risk of falls.” [28-30]
Regarding the relationship between postural control and fall risk, Moore cited a 1996 study in nursing home patients that did conclude that gait and balance disorders, as well as weakness, were significant contributors to fall risk, though it wasn’t clear to what extent these problems may have been related to other issues, such as peripheral neuropathy. He also noted a study from 2006 quantifying differences in the ability to recover balance between groups of young and elderly women; however, the study concluded only that “exercise-based fall prevention programs should include balance and agility training, in addition to strength training.” In addition, Moore cited a Turkish study showing that posterior leaf-spring AFOs improved balance and reduced the risk of falls, but it was conducted in poststroke patients with chronic spastic hemiparesis.
As noted, then, some of these studies may reinforce Moore’s claims, at least by extrapolation. But in other cases, applying the results of such research to the elderly, whose deficits are real but not identical to those with neurological problems, may be hard to justify.
Moore’s written responses make clear that his approach is tailored to the individual patient.
“Clearly the MBB is not for everyone,” he writes, “but I think the evidence for it in reducing fall risk by addressing weakness, instability, and ataxia is compelling.”
Pending further research (Moore said that two trials are underway, but did not indicate when results may be available), the issue will remain open to debate.
“Clinicians considering the use of such devices need to keep in mind that improvements in postural stability in controlled laboratory settings may not necessarily translate to a reduction in falls in the real world,” Menz pointed out. “Falls are multifactorial, and an individual’s underlying physiological falls risk is mediated by their level of exposure to potentially hazardous situations. I’m not ruling out the possibility that AFOs could prevent falls, but the only way to properly test these claims is to conduct well-designed randomized trials with prospectively documented falls—not lab-based measures of postural stability—as the primary outcome.”
|Focus on the patient|
In any case, the common theme that emerges through interviews with clinicians is the primacy of the individual being treated, regardless of the condition or the indications for an AFO.
“It’s definitely about finding what is appropriate for the patient,” said Chad Lairamore, who primarily sees those recovering from strokes and traumatic brain injuries. “It’s hard to say one approach is right in all situations. I always go with the least restrictive device I can, as long as the patient is safe—acknowledging that ‘safe’ is a subjective term.”
In his JPO article, Bryan Malas made the case that clinicians might best assess the impact of balance and postural issues in the context of their patients’ activities of daily living (ADL). He noted that when adult CP patients were asked to prioritize their goals, communication was at the top of the list, followed by ADL, mobility, and walking.
“I wondered, if we administered that survey to clinical professionals, if they would guess that those were the patients’ priorities?” Malas asked. “That’s a big piece we’re missing, because I don’t know that we would.”
He provided an example from his own practice. He’d just fitted a young girl with bilateral AFOs and had not yet optimized the alignment.
“Immediately she stopped talking, because she didn’t feel stable and all her attention was on balancing herself,” he said. “Then we put in some small wedges, changed the alignment, and all of a sudden she started talking to us again. Communication is important to her, and if I don’t optimize the AFO, I take it away. If I’m not facilitating my patients’ daily activities, then all the theory doesn’t matter because I’ve failed as a clinician. We can’t miss the most important piece here, which is the patient and what he or she wants.”
|Cary Groner is a freelance writer in the San Francisco Bay Area.|
Source Lower Extremity Review