Francis Cannard

TexiCare: an innovative embedded device for pressure ulcer prevention. Preliminary results with a paraplegic volunteer.

This paper introduces the recently developed TexiCare device that aims at preventing pressure ulcers for people with spinal cord injury. This embedded device is aimed to be mounted on the user wheelchair. Its sensor is 100% textile and allows the measurement of pressures at the interface between the cushion and the buttocks. It is comfortable, washable and low cost. It is connected to a cigarette-box sized unit that (i) measures the pressures in real time, (ii) estimates the risk for internal over-strains, and (iii) alerts the wheelchair user whenever necessary. The alert method has been defined as a result of a utility/usability/acceptability study conducted with representative end users. It is based on a tactile-visual feedback (via a watch or a smartphone for example): the tactile modality is used to discreetly alarm the person while the visual modality conveys an informative message. In order to evaluate the usability of the TexiCare device, a paraplegic volunteer equipped his wheelchair at home during a six months period. Interestingly, the first results revealed bad habits such as an inadequate posture when watching TV, rare relief maneuvers, and the occurrence of abnormal high pressures.

Foot ulcer prevention using biomechanical modelling

Foot 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 whether 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 stabilise the foot. This model simulates a realistic behaviour 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.

Influence of the calcaneus shape on the risk of posterior heel ulcer using 3D patient-specific biomechanical modeling.

AbstractMost 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.

Pressure sores prevention for paraplegic people: Effects of visual, auditory and tactile supplementations on overpressures distribution in seated posture

This paper presents a study on the usage of different informative modalities as biofeedbacks of a perceptual supplementation device aiming at reducing overpressure at the buttock area. Visual, audio and lingual electrotactile modalities are analysed and compared with a non-biofeedback session. In conclusion, sensory modalities have a positive and equal effect, but they are not equally judged in terms of comfort and disturbance with some other activities.

Patient-specific finite element model of the buttocks for pressure ulcer prevention – linear versus non-linear modelling

Currently available techniques and/or protocols designed to prevent pressure sore formation in persons with spinal cord injury and wheelchair users are mainly based on the improvement of the skin/support interface and on postural and behavioural education. These techniques, however, seem to lack efficiency as the prevalence and incidence of pressure sores still remains very high. This study outlines a methodology aiming at the definition of an individual and personalised pressure ulcer risk assessment scale based on patient-specific Finite Element modelling of the buttocks.

Multi-modal framework for subject-specific finite element model generation aimed at pressure ulcer prevention

This study outlines a methodology aiming at the definition of an individual and personalised pressure ulcer risk assessment scale based on patient-specific biomechanical modelling

Dynamic biomechanical modelling for foot ulcer prevention

This paper introduces a 3D Dynamic Finite Element biomechanical model of the human foot used for diabetic foot pressure ulcer prevention. The model estimates the internal strains and send an alert to the user in case of high strains values.

Foot biomechanical modelling to study orthoses influence.

Several pathologies of the foot can be solved simply by adding an orthosis under the patients foot. Defining the geometry and the size of such orthosis is key in optimizing its influence on the foot. Unfortunately, most of the orthoses produced today are not specifically design for a patient. They allow improvements to some degrees but could be more efficient if they were patient specific. We propose to use a patient-specific finite element foot model to study the influence of such orthoses and to help designing them in a better way, in accordance with the patients anatomy and pathology.

Biomechanical Modeling of the Foot

The foot exhibits a complex behavior during gait as it adapts to the ground geometry to ensure balance, but it also stores energy to ease the next step. Its subtle functionality can be affected by morphological issues, by aging, or by a disease such as diabetes. Hence, modeling the foot could improve our understanding and improve the treatment of pathological conditions. In this chapter, after presenting the foots anatomy and functionality, we propose a survey of the principal foot models in the literature. Then we introduce our biomechanical model, which uses the finite element method to represent several soft tissue layers around an articulated skeleton of the foot, along with cables simulating the action of ligaments. Two clinical applications, namely ankle arthrodesis and foot ulcer prevention, are also presented.

Using Sensory Substitution of Median Sensory Deficits in the Traumatized Hand to Develop an Innovative Home-Based Hand Rehabilitation System

Post-traumatic median nerve sensitive deficits are frequent. They are a source of permanent handicap that dramatically decreases the level of autonomy and the quality of life of persons suffering from these deficits. Surgical repair is possible, but the results are not always functionally useful. Therefore, prosthetic approaches do represent an alternative solution that needs to be explored. Along these lines, this paper describes an innovative home-basedhand rehabilitation systemdevice that exploits sensory substitution of median sensory deficits in the traumatized hand. It is composed of a glove bearing smart textile pressure sensors and a wristband providing vibratory biofeedback to the user. The goal of this sensory-substitution system is to provide for patients an effective method to compensate the lack of sensitivity of the finger pads and to recover a functional hand use. This innovative system is intended to be employed for assessment, training and rehabilitation exercises at home.