Abstract:

Significance The diabetic foot is a serious chronic complications in diabetic patients and is characterized by high rates of disability, death, and recurrence. 50% of diabetic foot ulcers and amputations can be avoided through early screening, but only 15.7% of diabetic patients are screened regularly. Studies have shown that monitoring the skin temperature of diabetic patients' feet helps to detect foot abnormalities, and reduce the risk of primary and secondary diabetic foot. Currently, smart footwear for monitoring foot temperature in the diabetic foot has developed, such as Siren Diabetic Socks and SmartSox Socks. However, the willingness of patients for wearing diabetic footwear is low, and medical professionals suggest that there is still a lack of strong evidence for the diagnostic value of such products. Therefore, a comprehensive and scientific analysis of smart footwear for monitoring temperature in the diabetic foot can help improve the systematic understanding of these products among diabetic patients and related researchers, increase the popularity and usage rate, and provide theoretical references for future research.

Progress In order to systematically and objectively understand the mechanism and product efficacy of smart footwear for monitoring foot temperature, the differences in plantar temperature characteristics between different types of diabetic patients and healthy people were compared. Thermograms from the healthy people showed a symmetrical butterfly pattern with the medial arches showing the highest temperatures, while in diabetics, due to inflammation caused by neuropathy, abnormal thermoregulation, and local ischemia caused by peripheral arterial disease, the foot temperature is often higher than that of healthy feet, and the distribution is irregular, with higher temperatures in areas at high risk of ulceration. In order to fully extract the predictive value of temperature, there mainly exist three types of index extraction methods, i.e., thermal symmetry of foot, in dependent limb regional temperature difference, and temperature stress analysis. A 2.2 ℃ difference between contralateral spots is the most widely used as the predictive threshold of diabetic foot disease, and the predictive sensitivity and specificity are often improved by continuous duration-assisted analysis. Recently, smart footwear targeting foot temperature monitoring has been developed. The Optical-Fiber-Based Smart Sock has the advantages of multi-index monitoring, comfortable and reusable. However, there are still differences in the number of temperature sensors and monitoring areas between products. The main monitoring areas are heel, medial midfoot, first metatarsal head, fifth metatarsal head, and first toe.

Conclusion and Prospect The effectiveness of using temperature monitoring to prevent diabetic foot has been unanimously recognized by researchers. It is clinically meaningful to use the temperature difference of 2.2 ℃ between contralateral spots as the prediction threshold for diabetic foot. Nontheless, the individual baseline temperature differences should be taken into consideration, assisted with other indicators such as the duration of temperature difference and pressure, so as to improve the predictive sensitivity and specificity of smart footwear. In the future, the risk level can be identified based on the foot temperature values and distribution patterns of diabetic patients under different activity intensities based on big data, and other indicators such as pressure, shear stress, toe range of motion, humidity, pH, and sweat-based glucose level can be studied in depth to predict the potential value of diabetic foot risk, explore the relationship between the indicators, and dissect the diabetic foot development risk mechanism together with skin temperature. In addition, machine learning can be used to optimize early warning algorithms, automatically calculating and updating the typical foot temperature pattern individualized. Finally, the overall system of shoes and socks needs to be comprehensively explored regarding the care and prevention of diabetic foot.

Key words: diabetic foot, skin temperature, temperature sensor, smart wearable product, footwear, risk prediction