Biomechanical simulation of the Charcot neuroarthropathic foot with plantar ulcer

Abstract

Diabetic patients with long-term diabetes are mainly affected by peripheral neuropathy. This can lead to the Charcot neuropathic osteoarthropathy (CNO). The CNO results in dramatic deformities and dysfunctional foot and ankle complex. The gait and stance are modified and overloads occur because of overpressures below the bony prominences. As the neuropathy makes the region insensitive to pain, foot ulcers can appear. Currently, there is no way to predict foot ulcer resulting from the foot anatomy reconfiguration induced by CNO. The purpose of this study is to address this issue. A Type 2 CNO foot was reconstructed using the CT-scan modality and the corresponding biomechanical finite element (FE) model was created. This model includes bones as rigid bodies and represents the soft tissues of the foot as two different sub-domains. The sole of the foot model is put in contact with a virtual horizontal pedobarographic platform. The Charcot patient was asked to perform a static standing acquisition of plantar pressures using a Zebris platform. The collected pressures were applied on the FE foot sole in order to compute internal strains. Then, the foot model including gravity and contact with the virtual pedobarographic platform was used to simulate a standing position. The corresponding sole pressure and internal strains thus computed can therefore be respectively compared with the measured standing plantar pressures and with the internal strains simulated from the measured boundary conditions. The volumes and location of the largest clusters with contiguous nodes with Von Mises (VM) strains over 20% or 50% are similar (errors < 5%) between measured pressure applied and static simulations. The simulated peak pressure value is also close to the one measured with the patient in weight bearing position. The FE model of the type 2 CNO can predict, in weight bearing position, the location and the proportion of the Von Mises Strains in the soft tissue of the diabetic foot. The location is similar to the real plantar ulcer for this patient and the plantar pressure values are in accordance with the measurements. Indeed, a peak pressure value of 19.6 N/cm 2 is simulated in regard of the cuboid bone, which happens to be the actual location of the ulcer.