Finite element model of the forefoot interface with accommodative footwear orthoses

Ulcers in the plantar soft tissue has been identified as a major problem in patients with neuropathy of the foot, particularly those suffering from diabetes mellitus. Elevated plantar pressure has been identified as a primary risk factor in ulceration. Current practice is to apply a footwear intervention at the foot-shoe interface to reduce plantar pressure levels. At present, there is little biomechanical data in the literature to aid in understanding how such orthoses can effectively be applied. The present study proposes finite element models which can be used in conjunction with clinical measurements to gain insight into the effectiveness of a given orthosis. The models are two-dimensional sagittal plane sections of the forefoot through the axis of the second metatarsal. The models contain between 1053 and 2025 nodes, and between 880 and 1840 bilinear continuum elements. Linear material properties are assigned to the bone, and hyperelastic material behavior is specified for the soft tissue and footwear orthoses. Sliding interface elements are employed at the foot-footwear interface. Vertical loads are applied to the metatarsal bone. Normal stress at the foot-footwear interface is compared with clinical plantar pressure measurements for similar tissue configurations (normal tissue and reduced, diabetic neuropathic tissue). A study is performed using insoles of varying thicknesses of elastomeric foam. The resulting peak plantar pressure values compare well with clinically measured values.