'Smart' Insoles Reduce Diabetic Foot Ulcer Recurrence

BERLIN — Wearing pressure-sensing smart insoles (SurroSense Rx, Orpyx Medical Technologies) reduced diabetic foot ulcer recurrence by up to 86% in compliant patients in a randomized single-blinded trial in high-risk individuals with type 1 and 2 diabetes.

Neil Reeves, PhD, professor of musculoskeletal biomechanics, Manchester Metropolitan University, UK, presented the results here today at the European Association for the Study of Diabetes (EASD) 2018 Annual Meeting.

"By using a plantar pressure-sensing smart insole device, the feedback of pressure information in the intervention arm reduces ulcer recurrence by 71%, and furthermore in the compliant patients, this further increased benefit, with an 86% reduction in ulcer recurrence [compared with controls]," he reported.

Reeves explained that the lifetime risk of diabetic, neuropathic, plantar first foot ulceration is 25% and ulcer recurrence rates for patients with a history of diabetic ulcer is about 65% within 5 years, with up to 25% progressing to some level of amputation. To date, effective ulcer prevention strategies remain elusive, so there is a huge unmet medical need for novel approaches.

With this in mind, the study was designed to investigate the efficacy of pressure-sensing smart insoles for reducing diabetic foot ulcer recurrence in high-risk patients.

The insoles work by measuring plantar pressures and a smartwatch display alerts the user as to when pressure-induced damage is occurring, so that they can adjust their walking strategy appropriately and try to avoid complications.

"Plantar pressures [the pressure field that acts between the foot and the support surface during everyday locomotor activities] are regarded as a relatively accurate proxy for diabetic foot ulcer risk," Reeves explained.

Reduction of Up to 86% in Wearers of Smart Insole

All 58 randomized participants had type 1 or 2 diabetes, a history of plantar foot ulcers, diabetic peripheral neuropathy, and the ability to walk independently for at least 30 steps. The endpoint was incidence of plantar diabetic foot ulcer.

Both intervention and control groups in the single-blinded study wore the same device, comprised of a thin insole sensor that fits into a shoe lying underneath the foot and a pod that sits on top of the shoe. The device wirelessly relays information to a smart watch worn by the user, but only participants in the intervention group received sensor feedback.

The insole consisted of eight discrete sensors distributed around the sole of the foot. When high pressure was experienced, an alarm and a visual notification on the smart watch were triggered showing the location of the high pressure. In this scenario, patients were asked to follow the directions displayed on the watch — to walk around for 2 minutes and, if the pressure continued, actively take weight off the foot, remove their shoe, and check for foreign bodies.

Patients visited the clinic on a monthly basis for an ulcer check using images that were verified independently. Follow-up was at 18 months or until a plantar ulcer occurred.

Of the 32 patients in the intervention arm, 17 withdrew from the study, compared with seven withdrawals out of 26 patients in the control arm. Analyses were conducted on an intent-to-treat basis.

Reeve reported that there were 10 ulcers in 8638 person-days in the control group and four ulcers in 11,835 person-days in the intervention group.

"There was a significant 71% reduction [incident rate ratio (IRR), 0.29; P = .037] in the risk of re-ulceration in the intervention group [with smart insoles with feedback] compared to controls," said Reeves.

Patients in the intervention group wore the insoles for an average of 6.1 hours/day versus 6.9 hours/day in the control group. Upon adjustment for compliance, of the 40 patients who wore the device over 4.5 hours/day (18 in the intervention group, 22 in the control group), there were 10 ulcers from 6308 person-days in the control group compared with two ulcers from 9077 person-days in the intervention group.

This translated to an 86% reduction in risk of re-ulceration in the intervention versus control group (IRR, 0.14; P = .011).

"In a survival analysis, adjusting for compliance, an estimate of time-to-ulcer showed no significant difference between groups, but visually the curves are seen to separate around 6 months," reported Reeves.

He added that a further analysis of individual ulcerated feet for compliant patients showed a significant difference with longer time to ulceration in the intervention arm compared with controls.

Patients Regain Control but Work Involved Might Impact Participation

The overall ulcer rate in the study was low, at 17%.

"This might be explained by a number of factors, including the implementation of gold standard guidelines throughout the UK, and that in the present study we saw patients every month which is more than with standard of care," remarked Reeve.

He added that a possible mechanism for the success of the device was related to pressure off-loading "afforded by providing patients with plantar pressure feedback."

"In these patients, that [natural] feedback was lost many years ago due to diabetic peripheral neuropathy, so in that respect we suggest patients have been empowered to take control of their health in a way they hadn't been able to since the onset of significant diabetic peripheral neuropathy."

Commenting on the work, Solomon Rosenblatt, MD, an endocrinologist from Berkley affiliated with Beaumont Hospital-Troy, Michigan, questioned Reeves on why so many patients dropped out of the study. Of the 32 patients in the intervention arm, 17 withdrew from the study, versus seven out of 26 in the control arm.

Reeves answered: "We looked at a number of baseline factors including diabetic peripheral neuropathy and duration of diabetes, among others, between the drop-outs and those that remained in the study, and we found no significant difference."

"We need to look at this further but we speculate it might be related to the technology and the patient expectation of what they need to do to participate in terms of charging the device and the effect on their time," he added.

Rosenblatt continued his questioning, asking about the location of ulcers and relationship to the pressure sensors.

Reeves said he couldn't provide all the answers now but that analysis was continuing, "and we will have these data in the future."

Funding for the study was provided by Diabetes UK (years 1 to 3) and Orpyx Medical Technologies (study extension, year 4). Reeves has reported no relevant financial relationships.

European Association for the Study of Diabetes (EASD) 2018 Annual Meeting; October 2, 2018; Berlin, Germany. Abstract 7.

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