Smart insoles to prevent foot ulcers

Various companies around the world are busy developing smart insoles to prevent foot ulcers. These insoles mainly target plantar pressure measurements, as there is proven clinical benefit in reducing plantar pressure using therapeutic footwear that is being worn (see here and here). As with many medical devices, companies can be quick to point at potential benefits, but the needed research behind such claims is often lacking. A new study from Bijan Najafi and David Armstrong from the US, using commercially available smart insoles, is therefore an important contribution to shed some light on this.

Najafi and his team followed 12 patients with either an ulcer or a recently healed ulcer who wore a pair of smart insoles for three months. These patients received alerts when their pressure was exceeding 35-50mmHg for more than 15 minutes. Based on these alerts, patients had to offload their feet. The researchers subsequently analysed what worked better: fewer or more alerts. Their findings are intriguing and worth a closer look.

The major finding of the study is that patients who received more alerts increased their adherence to wearing the insoles, whereas this reduced in patients who received fewer alerts. Patients who received more alerts also reacted more quickly to them. This conflicts the idea that patients will become tired of the alerts. On the contrary, patients seemingly need to be kept vigilant of their risk of high plantar pressures.

However, another explanation is also possible: patients who understood the smart insoles better received more alerts, and became more adherent. These patients, as a result of better understanding the insole, reacted more quickly (8.8 minutes vs. 57.3 minutes). And as a result of these quicker reactions, they could receive more alerts. After all, when one alert lasts for almost one hour, patients cannot receive another alert in that period. And because these patients understood their insoles better, they were more willing to engage with them, and to adhere to wearing them. Unfortunately, this potential explanation cannot be examined with the data presented in this study.

From the paper, it is unclear how the ‘response to the alert’ is defined. Professor Najafi, key-note speaker at the DFA conference in September, provided further information via email:
Subjects were instructed the following steps in response to an alert (all these instructions could be also seen on SmartWatch via a help function): i) If the alert happened during sitting or standing, they were recommend to walk few steps until the alert was turned off. Alternatively, the subject could lift their foot if she/he was on sitting position. ii) If the above step was unsuccessful or the alert was returned immediately, the subject was recommended to check tightness of shoes, inspect the inside of their shoes, inspect their socks, inspect their feet for sign of skin irritation or callus, or inspect their insoles. iii)If the above steps didn’t work, the subject was recommended to contact a podiatrist. In our sample, the above instructions seemed to suffice.

These instructions move the insoles away from being ‘pure’ plantar pressure measuring insoles. They almost acted as ‘activity coaches’, with pressure used to understand what patients were doing at their home. It is possible that the more adherent patients felt empowered to change their offloading, because of their understanding and maybe because they were more successful after following the instructions. Whereas the non-adherent patients either did not know how to change this, or were unsuccessful and decided to let the alert run and ignore it.

The authors acknowledge the limitation of the small number of participants in this study. And as no ulcer developed in any of the patients (also not in those who were non-adherent), the potential of smart insoles to prevent foot ulcers, and the threshold that is needed for the alerts, cannot be investigated. Larger studies are needed, but despite the availability of this technique for some years now, are still not out there.

Smart insoles are still a promising intervention for foot ulcer prevention, but they have not moved from the ‘gadget’ state yet. Some exciting opportunities are shown in this paper, and some very interesting and thought-stimulating data is presented, but we are still far away from an evidence-based answer as to how to use these insoles in daily clinical practice.