Development of a gait analysis driven finite element model of the diabetic foot

Diabetic foot is an invalidating complication of diabetes mellitus, a chronic disease increasingly frequently encountered in the aging population. The global prevalence of diabetes is predicted to double by the year 2030 from 2.8% to 4.4%. The prevalence of foot ulceration among patients with diabetes mellitus ranges from 1.3% to 4.8%. Several studies have highlighted that biomechanical factors play a crucial role in the aetiology, treatment and prevention of diabetic foot ulcers. Recent literature on the diabetic foot indicates that mechanical stresses, high plantar pressures or/and high tangential stresses, acting within the soft tissues of the foot can contribute to the formation of neuropathic ulcers. While it is important to study the in-vivo diabetic foot-to-floor interactions during gait, models for simulations of deformations and stresses in the diabetic plantar pad are required to predict high risk areas or to investigate the performance of different insoles design for optimal pressure relief. The finite elements (FE) models allow taking into account the critical aspects of the diabetic foot, namely the movement, the morphology, the tissue properties and the loads. Several 2-dimensional (2D) and 3-dimensional (3D) foot models were developed recently to study the biomechanical behavior of the human foot and ankle. However, to the author knowledge, a geometrically detailed and subject specific 3D FE model of the diabetic neuropathic foot and ankle has not been reported. Furthermore 2D and 3D state-of-the-art FE foot models are rarely combined with subject specific gait analysis data both in term of ground reaction forces and kinematics as input parameters and plantar pressure for validation purposes. The purpose of the study herein presented was to simulate the biomechanical behavior of both an healthy and a diabetic neuropathic foot in order to predict the area characterized by excessive stresses on the plantar surface. To achieve this, it has been developed an FE model of the foot by means of applying the loading and boundary conditions given by subject-specific integrated and synchronized kinematic-kinetic data acquired during gait analysis trials to a subject specific FE model (geometry was obtained through subject specific magnetic resonance images - MRI). Thus, an integrated kinematic-kinetic protocol for gait analysis which evaluates 3D kinematics and kinetics of foot subsegments together with two comprehensive FE models of an healthy and a diabetic neuropathic foot and ankle were described herein. In order to establish the feasibility of the former approach, a 2D FE model of the hindfoot was first developed, taking into account the bone and plantar pad geometry, the soft tissues material properties, the kinematics and the kinetics of both an healthy and a diabetic neuropathic foot acquired during three different phases of the stance phase of gait. Once demonstrated the advantage of such an approach in developing 2D FE foot models, 3D FE models of the whole foot of the same subjects were developed and the simulations were run in several phases of the stance phase of gait The validation of the FE simulations were assessed by means of comparison between the simulated plantar pressure and the subject-specific experimental ones acquired during gait with respect to different phases of the stance phase of gait. A secondary aim of the study was to drive the healthy and the diabetic neuropathic FE foot models with the gait analysis data respectively of 10 healthy and 10 diabetic neuropathic subjects, in order to verify the possibility of extending the results of the subject specific FE model to a wider population. The validity of this approach was also established by comparison between the simulated plantar pressures and the subject-specific experimental ones acquired during gait with respect to different phases of the stance phase of gait. Comparison was also made between the errors evaluated when the FE models simulations was run with the subject specific geometry (obtained from MRI data) and the errors estimated when the FE simulations were run with the data of the 20 subjects