1) ObjectivesMost foot ulcers are the consequence of a trauma (repetitive high stress, ill-fitting footwear, or an object inside the shoe) associated to diabetes. They are often followed by amputation and shorten life expectancy. This paper describes the prototype of the Smart Diabetic Socks that has been developed in the context of the French ANR TecSan project. The objective is to prevent pressure foot ulcers for diabetic persons. 2) Material and methodsA fully wireless, customizable and washable "smart sock" has been designed. It is made of a textile which fibers are knitted in a way they provide measurements of the pressure exerted under and all around the foot in real-life conditions. This device is coupled with a subjectspecific Finite Element foot model that simulates the internal strains within the soft tissues of the foot. 3) ResultsA number of derived stress indicators can be computed based on that analysis, such as the accumulated stress dose, high internal strains or peak pressures near bony prominences during gait. In case of risks for pressure ulcer, an alert is sent to the person and/or to the clinician. A watch, a smart-phone or a distant laptop can be used for providing such alert.

Most posterior heel ulcers are the consequence of inactivity and prolonged time lying down on the back. They appear when pressures applied on the heel create high internal strains and the soft tissues are compressed by the calcaneus. It is therefore important to monitor those strains to prevent heel pressure ulcers. Using a biomechanical lower leg model, we propose to estimate the influence of the patient-specific calcaneus shape on the strains within the foot and to determine if the risk of pressure ulceration is related to the variability of this shape. The biomechanical model is discretized using a 3D Finite Element mesh representing the soft tissues, separated into four domains implementing Neo Hookean materials with different elasticities: skin, fat, Achilles' tendon, and muscles. Bones are modelled as rigid bodies attached to the tissues. Simulations show that the shape of the calcaneus has an influence on the formation of pressure ulcers with a mean variation of the maximum strain over 6.0 percentage points over 18 distinct morphologies. Furthermore, the models confirm the influence of the cushion on which the leg is resting: a softer cushion leading to lower strains, it has less chances of creating a pressure ulcer. The methodology used for patient-specific strain estimation could be used for the prevention of heel ulcer when coupled with a pressure sensor.

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International audienceFoot ulcers are a common complication of diabetes and are the consequence of trauma to the feet and a reduced ability to perceive pain in persons with diabetes. Ulcers appear internally when pressures applied on the foot create high internal strains below bony structures. It is therefore important to monitor tissue strains in persons with diabetes. We propose to use a biomechanical model of the foot coupled with a pressure sensor to estimate the strains within the foot and to determine if they can cause ulcer formation. Our biomechanical foot model is composed of a Finite Element mesh representing the soft tissues, separated into four Neo Hookean materials with different elasticity: plantar skin, non-plantar skin, fat and muscles. Rigid body models of the bones are integrated within the mesh to rigidify the foot. Thirty-three joints connect those bones around cylindrical or spherical pivots. Cables are included to represent the main ligaments in order to stabilize the foot. This model simulates a realistic behavior when the sole is subjected to pressures measured with a sensor during bipedal standing. Surface strains around 5 % are measured below the heel and metatarsal heads while internal strains are close to 70 %. This strain estimation, when coupled to a pressure sensor, could consequently be used in a patient alert system to prevent ulcer formation

Footwear comfort is essential and pressure distribution on the foot was shown as a relevant objective measurement to assess it. However, asperities on the foot sides, especially the metatarsals and the instep, make its evaluation difficult with available equipment. Thus, a sock equipped with textile pressure sensors was designed. Results from the mechanical tests showed a high linearity of the sensor response under incremental loadings and allowed to determine the regression equation to convert voltage values into pressure measurements. The sensor response was also highly repeatable and the creep under constant loading was low. Pressure measurements on human feet associated with a perception questionnaire exhibited that significant relationships existed between pressure and comfort perceived on the first, the third and the fifth metatarsals and top of the instep. Practitioner Summary: A sock equipped with textile sensors was validated for measuring the pressure on the foot top, medial and lateral sides to evaluate footwear comfort. This device may be relevant to help individuals with low sensitivity, such as children, elderly or neuropathic, to choose the shoes that fit the best.