December 2016

Can activity monitoring improve wound healing?

Typical interventions in patients with active diabetic foot ulcers include offloading devices and a decrease in activity. And an increasing number of tools are becoming available to help lower extremity clinicians determine how well their patients are actually adhering to such interventions.

By Cary Groner

Caring for the lower extremity complications of diabetes is complex and demanding. Peripheral neuropathy affects more than half of diabetes patients and is associated with an increased risk of diabetic foot ulcers, which themselves raise a patient’s chances of infection, amputation, and death.1 And, although LER reported in 2011 on research showing weightbearing exercise is generally good for neuropathy patients and doesn’t increase plantar ulcer risk2— particularly if the regimen is consistent and avoids sudden spikes of activity3—clinicians agree exercise must be modified when an ulcer is present.

In people without diabetes, this is, to some extent, common sense: You’re less likely to go for a run if your new shoes just gave you a painful blister. But, due to decreased sensation in the extremities, patients with neuropathy often don’t realize they’re getting an ulcer until it has already formed.1

Aside from appropriate wound care, typical interventions include offloading and a decrease in activity.4 Clinicians acknowledge these two may go hand in hand, moreover, in that certain offloading strategies such as total contact casts (TCCs), by their nature, make it harder for patients to remain active. And an increasing number of tools are available with which clinicians can determine how well patients are actually adhering to such limitations, particularly when removable devices are prescribed.

Moving targets

“There’s a difference between recommended activity levels for prevention and those once an ulcer is present,” said Michael Mueller, PT, PhD, a professor of physical therapy at the Washington University School of Medicine in St. Louis. “Once a foot has an ulcer, it’s an insidious process, and the risk of subsequent ulcers and amputations shoots up. You have to protect that tissue to allow it to heal, but there lies the dilemma, because ideally you’d want that person to remain active and continue to stress the other tissues so they don’t deteriorate.”

So how to strike a balance?

“That’s the million-dollar question,” Mueller said. “Every patient is different, and the decisions you make have to relate to their disease status, their prior activity levels, how much deformity they have, and what their peripheral blood flow is like; there’s a list of variables that create a moving target.”

Certain strategies for offloading diabetic foot ulcers, such as total contact casts, may help promote wound healing by making it difficult for patients to remain active.

For Mueller, the best clinical approach is fairly traditional: offload the area and gradually increase activity when the ulcer has healed. But questions remain.

“From a clinical standpoint, once those tissues are healed and we begin to stress them again, that’s where we know the least,” he said. “The beauty of total contact casts, as well as more recent alternatives such as the walking boot and other offloading devices, is that they allow the patient to be up and around but reduce localized tissue stress. We want to minimize what is often a high rate of reulceration, because getting it healed is a big deal, but keeping it healed is even more challenging.”

Michael Pinzur, MD, a professor of orthopedic surgery and rehabilitation at Loyola University Medical Center in Maywood, IL, agreed it can be demanding to devise treatment plans for a diverse group of patients. He emphasized, however, that offloading doesn’t mean nonweightbearing, but rather a redistribution of load over a bigger surface area, which can be accomplished in a number of ways.

“The value of the total contact cast is not only that it distributes load, but that it decreases shear, and shear is the real enemy,” Pinzur explained. “If you put patients in a TCC you control swelling, decrease shear, and distribute load. A walking boot will do nearly as well, and in some cases you can use a shoe with an elastic dressing. There are many options, and it depends on the patient’s unique combination of static and dynamic factors.”

Complications

A variety of issues complicate decisions about which offloading device to prescribe, partly because patients may be more active in some than in others at a time when activity isn’t necessarily a good thing. A 2013 Cochrane review concluded that nonremovable TCCs are the most effective means of healing diabetic foot ulcers.5 Despite such findings—and the clinicians LER spoke with were all well familiar with the research—removable cast walkers are prescribed much more often.6

The problem is that, although such walkers provide offloading equivalent to that of TCCs, they’re associated with poorer out­comes,7 and most clinicians suspect this is because patients remove them. In fact, studies have found a direct association between wound healing and how much removable devices were actually worn,8 and one paper determined that unprotected standing may pose even more of a threat than walking.9 Investigators have shown patients tend to be noncompliant for reasons that include the devices’ weight, their effects on gait, and most important, their negative influence on postural stability.10,11

“Total contact casts get the best outcomes,” said Ryan Crews, MS, CCRP, a clinical research scientist and an assistant professor in the Department of Podiatric Surgery and Applied Biomechanics at Rosalind Franklin University in Chicago. “But, from a practical standpoint, people are using a lot more of the removable devices.”

An issue closely related to compliance has to do with the nature of the impairments associated with neuropathy. The condition often entails more than a loss of sensory input from the extremities; it can also lead to muscle weakness and atrophy that affect motor control, and all these factors together may impair joint stability and balance.12 Neuropathy has cognitive implications, as well.13

“You hear complaints that diabetic patients are noncompliant with treatment,” Pinzur said. “But your brain is made of nerves, and people with neuropathy tend to have cognitive and judgment deficits.”

David Armstrong, DPM, MD, PhD, a professor of surgery and codirector of the Southern Arizona Limb Salvage Alliance (SALSA) at the University of Arizona College of Medicine in Tucson, concurred.

“Diabetic neuropathy can cause serious damage to the gray matter of the brain,” he said, “which is a major component of the central nervous system involved in touch and pain perception.14 These patients have lost the gift of pain, so we need strategies that accommodate differences in behavior and may even serve as sensory substitutes.”

With regard to activity, those strategies include monitoring devices such as insoles that alert patients when they exceed a pressure threshold level in a high-risk region of the plantar surface, specialized mats that detect significant asymmetries in skin temperature between feet, and activity monitors that let clinicians know the extent to which patients are using their offloading devices.

Activity monitors often have been used for research, which has consistently documented poor compliance with device wear. UK investigators reported that only 22% of their patients wore their prescribed footwear all day,15 and a similar US study found that just 28% of patients wore theirs more than 80% of the day.16 Such data have obvious implications for clinicians’ activity recommendations.

“Ideally, I’d like to be able to titrate activity the way we titrate a drug,” Armstrong said. “These relatively inexpensive tools let us track activity, or modify it based on plantar temperatures.”

Not everyone agrees on the practical value of such technology, however. For example, Mike Mueller told LER that, in his experience, plantar thermometry faces challenges that may limit the extent to which it is used outside of the research setting.

“We’ve found temperature measures to be highly variable,” Mueller said. “We had people coming in every day with differences of four degrees between areas of their feet, but there weren’t any other signs of inflammation or problems. At the beginning we tried to get them to limit their activity, but it happened so frequently that people would finally say they couldn’t do it. The temperature differences didn’t seem to have any negative repercussions, so the bottom line was that, in our hands, the approach wasn’t all that sensitive.”

Mueller noted his team’s methods weren’t identical to those described by Lavery and Armstrong,17 which might have partly explained the discrepancy.

Armstrong, who has served on the scientific advisory boards of companies that make monitoring devices, responded that the relative usefulness of such interventions depends partly on the severity of the patient’s condition.

“These kinds of tools don’t help very low-risk patients,” Armstrong explained. “But the higher risk you get, the more event rates you get, so the less you’re crying wolf. Another benefit we’re seeing with the tools that are measuring many spots is that you can use the mathematics of machine learning to look for patterns that might be too complicated for one person to get if they’re just manually checking ten spots on each side. As with a lot of such tools, the key is to filter, to find the optimal combination of sensitivity and specificity.”

Again, in this context, the discussion frequently returns to an individual patient’s capabilities.

“I’m not saying temperature monitoring isn’t useful,” Mueller said. “But patients get easily frustrated and overwhelmed, and they’re loath to follow lots of instructions. If they can’t manage factors such as blood glucose, how are they going to manage how many steps they take in a day?”

To address such concerns, some clinicians are collaborating to develop monitoring systems that shift some responsibility from the patient to the physician. Joseph LeMaster, MD, MPH, an associate professor in the Department of Family Medicine at the University of Kansas Medical Center in Kansas City, is working with Armstrong on such a proposal, but there’s work to be done.

“Implementation at the practice level would require facilitation of staff, including nurses and doctors, and providing support for those practices that aren’t currently in place or reimbursed, including various types of monitoring devices,” LeMaster said. “Again, though, the issue is not only can you get it reimbursed, but can you get people to use it?”

For Ryan Crews, monitoring might also be useful to bolster treatment decisions.

“If you start by default with a removable device, but you see that the patient isn’t wearing it, having those objective data could give you justification for switching to something the patient can’t remove,” Crews pointed out.

Keep moving, folks

One challenge for clinicians, of course, is finding ways to heal an ulcer without the rest of a patient’s body crumbling due to inactivity.

“I think we need to develop treatments that let the patient be as functional as possible, because if they heal with nonweightbearing and then break down again as soon as they’re bearing weight, you’ve wasted that whole period of their life,” Pinzur said.

He added that clinicians must assess a variety of variables to make decisions about a patient’s appropriate activity level. These include quality of diabetes control, cognitive capabilities, and wound classification.

“I use different modalities in different patients depending on my assessment of their risk,” Pinzur said.

Crews and his colleagues are developing innovative ways around the activity limitations imposed by diabetic foot ulcers.

“We want to figure out how to let patients be active but keep the wound safe,” he said. “One idea is that they could be on a stationary bike and use a nonstandard cleat to restrict the stress to the nonwounded area of the foot.”

In a recent study testing this approach in individuals at risk for developing foot ulcers, Crews reported the cleat significantly reduced forefoot plantar pressure and improved tissue perfusion without increasing foot temperature, suggesting it could now be tried in patients with active ulcers.18 The paper noted there are a number of mechanisms by which exercise could benefit ulcer healing, including improved microcirculation in the foot, which would increase nutrient and oxygen delivery to a wound and possibly enhance the body’s anti-inflammatory responses as well.

“Ultimately, our goal is to find a way for patients to stay active without making the wound worse,” Crews said.

As he and other researchers continue to develop such approaches, patients may find themselves with healing options that include more overall activity.

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

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