Antoine Perrier

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.

3D musculoskeletal finite element analysis of the foot kinematics under muscle activation with and without ankle arthrodesis

The choice between arthrodesis and arthroplasty in the context of advanced ankle arthrosis remains a highly disputed topic in the field of foot and ankle surgery. Arthrodesis, however, represents the most popular option. Biomechanical modeling has been widely used to investigate static loading of cadaveric feet as well as consequences of arthrodesis on bony structures. Although foot kinematics has been studied using motion analysis, this approach lacks accuracy in capturing internal joints motion due to limitations inherent to external “marker sets” and the fact that it imposed the foot to be considered as a rigid solid. The consequences of arthrodesis on kinematics of the unloaded foot are not well understood although it is of crucial importance during the swing phase and at heel contact. Investigating ankle mobility during muscle contraction with and without arthrosis could explain how the motion is produced by extrinsic muscles activations affected by an arthrodesis. This study aims at defining if a biomechanical model with Finite Elements could help arthrodesis understanding.

Conception and evaluation of a 3D musculoskeletal finite element foot model.

This paper introduces a new patient-specific musculoskeletal and Finite Element (FE) model of the foot aimed to be used in the context of deep pressure ulcer prevention, orthopedic and motion analysis. This model is evaluated in both static and dynamic frameworks.

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.