Smart insoles: Assessing their clinical potential

Athletes have been quick to embrace smart insoles and the biomechanical data generated by the devices’ embedded sensors. But experts believe smart insoles may also have potential clinical applications for patients with foot health problems, such as diabetic neuropathy.

By Shalmali Pal

Wearable devices to track exercise and fitness have become ubiquitous in the workout environment, but more often than not, these are basically fancy pedometers. Enter smart insoles, or footwear inserts with embedded sensors, whose developers claim they produce enough legitimate data on the user’s biomechanics to fill a medical file.

Although not as sophisticated (or as expensive) as in-shoe measurement systems used for research, the new generation of smart insoles can measure location, foot pressure, stride length, and more in real time. The data are then sent via wireless technology to a mobile computing platform—tablet, smart phone, smart watch—that allows the user to interact with the information through the software.

“These kinds of tools are going to be a new measure of quality of life, and of how people move through their world,” said David Armstrong, DPM, MD, PhD, a professor of surgery at the University of Arizona College of Medicine and director of the Southern Arizona Limb Salvage Alliance (SALSA), both in Tucson.

Many of these devices have been adopted by athletes—runners, in particular—who are keen on self-management and, not surprisingly, interested in the nitty-gritty details of their performance. But do smart insoles have a part to play in helping people with foot health problems, such as diabetic neuropathy? LER: Foot Health spoke with an international group of biomechanical experts to get their take on how “smart” these insoles really are.

What’s out there?

A 2014 white paper on smart textiles, garments, and fabrics, including wearable technology, noted the global market for these products is expected to be worth $1.5 million by 2020.¹ The main growth sector since 2011 has been in the protection and military clothing sector, but sports and fitness applications, following by health and medical, are expected to see major advances.

Just doing a Google search for “smart insoles” yields more than 800,000 results. In many cases, these are products that are currently on the market; in others, they are links to crowd-sourcing pages to fund development of experimental products.

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One example is Feetme’s smart inner insoles, each with 80 pressure sensors, which provide real-time gait analysis via a smart phone, and may prove useful for patients with diabetes to monitor foot pressure and potentially prevent ulcers.²

Alexis Mathieu, cofounder and chief executive officer of the Paris, France-based company, said the main target consumers for the insoles are runners and patients with diabetes. Mathieu said the company has conducted one clinical trial with its smart insole, and is in the process of setting up another, but declined to share study details or results.

Made by Orpyx Medical Technologies of Calgary, Canada, Surrosense Rx is a sensor-embedded insert that captures pressure data from feet. The data are sent wirelessly to a smart watch device (which is packaged with the insoles). According to the company, the “smart watch alerts you when dangerous time and pressure levels are detected, so you can modify behavior and avoid damage.”³

The market for Surrosense Rx is patients with diabetes. Bijan Najafi, PhD, director of clinical research in the Division of Vascular Surgery and Endovascular Therapy at Baylor College of Medicine in Houston, and colleagues recently conducted a pilot study⁴ to test the recurrence of diabetic foot ulcers in patients using the device, which is considered a class I medical device and therefore is exempt from FDA 510(k) premarket review.

The study included 21 patients with diabetic neuropathy and recently healed ulcers. The participants received an average of 3.38 daily alerts per day, of which nearly 44% were successfully managed, Najafi said. In addition, the majority of the alerts (45.8%) were related to pressure changes under the metatarsal heads, which is one of the plantar surfaces that is most prone to ulceration.

The preliminary data, presented at the 2015 International Symposium on the Diabetic Foot, showed no serious adverse events with the device, and more importantly, no reulceration or foot
problems during active use of the device or during the three-month follow-up period after discontinuing use of the device. However, when self-reported utilization was compared to sensor-based wear time, results showed patients tended to overestimate their time spent using the device, leading the authors to caution that “patient adherence to [mobile health] technology is highly dependent on user interface, number of false alarms, and level of comfort.”

For additional examples of smart insole technology, see the sidebar below.

Real-time feedback and a “user-friendly” interface are two factors that can make a smart insole stand out, said Najafi, who is also director of Interdisciplinary Consortium on Advanced Motion Performance (iCAMP) at the University of Arizona, where the pilot study was conducted. The study was partially funded by Orpyx.

“The big challenge is still how to visualize or feed back key information to patients for assisting them to take care of their own health,” Najafi said. “Another key challenge is how to engage patients to continue wearing these insoles.”

For Armstrong, a coauthor on the study, smart insoles like Surrosense Rx that rely on sensory substitution technology—or the use of one sensory modality to supply environmental information normally gathered by another sense while still preserving some of the key functions of the original sense—will have the longest staying power in the market.⁵

“There are other kinds of insoles that measure pressure or temperature, but most of them haven’t reached the same level of sophistication as the sensory substitution devices,” he said.

And, even the devices that are driven by more sophisticated software still contend with the challenge of being user-friendly and comfortable.

“Right now, the form factor of smart insoles is like the early days of the cell phones, when the phones were large and clunky,” Armstrong explained. “That form factor was good, but it was uncomfortable. Eventually, we evolved to the smart phone, which is much smaller in comparison. There are some insoles right now that are good products, but they are unwieldy and not necessarily
practical.”

Rob Conenello, DPM, immediate past president of the American Academy of Podiatric Sports Medicine, and a podiatrist with Orangetown Podiatry in New York, said he does not currently use smart insoles in his practice, though he is interested in doing so.

“I’ll go to a show, see a smart insole that interests me, and then six months later at another show, the device is that much better,” Conenello said. “My biggest concern is that…I don’t want to invest in a product that is basically going to become obsolete before I’ve really had a chance to use it.”

In addition, he said, many smart insoles offer quantitative data (eg, step counts), which isn’t necessarily what he’s looking for.

“I’d like more qualitative analysis from these devices, and I think that’s where they are headed,” he said.

Clinical value

Experts say the personalized feedback smart insoles can deliver to users and clinicians makes them a worthwhile consideration for practitioners looking to maintain contact with patients without extra in-person visits or waiting until an emergent situation arises.

Smart insoles can also help patients with self-management, Armstrong said. For instance, the smart insoles may alert a user with a healed diabetic foot ulcer that her activity level is outside the norm for her on a given day, and that this has led to pressure and temperature changes in the feet.

“This may make the patient realize that she’s been on her feet, running errands or something similar, for longer than she realized,” Armstrong said. “That perhaps it’s time to take a break.”

But, in terms of clinical applications, two major questions remain: What to do with all the data these insoles have the potential to generate, and how to get users to pay attention to it?

One drawback of these devices is the potential for “analysis paralysis,” Armstrong noted.

“When you start hitting people with reams of data, then that becomes something they will ultimately ignore,” he said. “How many apps do we have on our phone right now that are constantly sending us alerts or updates? And how many times do we actually access that information, or simply ignore it, over the course of a day?”

In fact, feedback received when patients are not experiencing symptoms can lead them to simply stop using the device.

“People don’t necessarily change their behavior unless something ‘breaks,’” he said. “They tend to distance themselves from their issues unless there’s a problem.”

Conenello said he likes the idea of getting complete information on how a person’s gait changes over time, in a real-world
setting.

“When I work with a patient or an athlete in the lab or office, I can’t replicate what they go through in their life or game play,” he explained. “There’s an advantage to obtaining that data in real-time. However, I also want good information from that device. I want that Aha! moment where the patient can see how and why they need to make changes, whether that’s in their movement patterns or in their footwear choices.”

Along with patients with diabetes, Conenello said he’d consider using smart insoles in patients with Parkinson disease, to show them changes in their gait and balance over time. For instance, performing the single-leg stance with the smart insole could give the patient visual feedback about weight distribution and how to make corrections for greater stability.⁶

He’d also consider using it for children with lower extremity movement disorders, such as lower limb spasticity related to cerebral palsy, to collect qualitative data on the gait cycle.⁷

The clinical usefulness of smart insoles will also involve the extent to which they are compatible with therapeutic footwear and functional orthotic devices, Conenello noted.

Experts agree that smart insoles don’t give clinicians a license to cut back on patient interaction.

“I think it’s the responsibility of the [healthcare provider] to fine-tune the use of the insoles,” Armstrong said. “You have to become what I call ‘an activity doctor,’ helping high-risk patients and their caregivers understand what information from the device is import­ant and what’s less important.”

While that will require a higher level of upfront engagement by healthcare personnel, Armstrong said, it fits well with the current trend in medicine to offer value-based, rather than volume-based, care.

“If a diabetic patient has a foot disorder that is in remission, the device can warn us if he is nearing the point of potential reulcer­ation. That’s where the value is,” he said.

The athlete’s foot

Athletes clearly have different needs and goals than patients with diabetes or other serious health issues with foot-related comorbidities, but some of the same questions about the value of feedback from smart insoles apply.

The technology’s benefits include device portability, the ability to do in-field measurements, and the potential to assist with shoe prescription for runners with a recent history or metatarsal stress fractures or hallux rigidus, said Richard Willy, PhD, PT, assistant professor in the Department of Physical Therapy at the College of Allied Health Sciences at East Carolina University in Greenville, NC.

Thor Besier, PhD, an associate professor at the Auckland Bioengineering Institute in New Zealand, noted that there are many examples of sensors and new sensing technology that are making in vivo force and pressure measurement possible.

“However, on their own, the data are less interesting and difficult sometimes to interpret,” said Besier, a codeveloper of I Measure U Run (IMU-Run) a wearable device that monitors tibial shock in runners.⁸ “Having these data inform a biomechanical model that can predict joint moments is really where they will add value to a runner.”

Drawbacks to the technology, according to Willy, are possibly low data sampling rates and sensor resolution, likely high cost and unknown durability, and variable calibration procedures.

Data overload is another potential pitfall, Besier said.

“An athlete can only focus on a few key pieces of information at a time, so being able to obtain such a huge amount of data over the course of a run is overwhelming,” he said.

Ideally, feedback should be simple and intuitive, allowing the user to adjust technique to modify the input signal. With the IMU-Run, “we are still exploring what key metrics might be useful to runners and learning how runners respond to receiving this feedback,” Besier said.

It’s also important to remember that any gait modifications—including those inspired by smart insole technology—come with both benefits and risks, Willy said.

“Any time a gait modification is undertaken, load is shifted elsewhere,” he said. “Thus, injury risk or metabolic demand may increase, particularly if the feedback does not include limits on a modification.”

For example, in runners with high impact forces, increasing running cadence by 5% to 10% over the runner’s preferred cadence can help reduce those impact forces by up to 20%.⁹ But increasing running cadence more than 10% over a runner’s preferred cadence also may increase metabolic demand—which, in turn, is likely to affect runner adherence.⁹

“Gait modifications should not be undertaken unless there is a specific need and a specific parameter of gait that should be changed,” Willy said.

Besier said he believes the best use of such devices will be for each user to understand his or her own body and its response to loading.

“The more our sensors become integrated into the standard ritual of your daily run, the more likely they will have a chance to make a true impact on your performance,” he said. “Ultimately you should not even be aware that the sensors are there. You just get dressed and get on with your run.”

Shalmali Pal is a freelance writer based in Tucson, AZ. 

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