Analysis of Mechanical Behavior of the Underlying Soft Tissue to Ischial Tuberosities Using Finite Element Method

Abstract

The pressure injuries are a secondary complication of spinal cord injury. A strategy to prevent them is advancing support surfaces, like wheelchair cushions or mattress that redistributed the body weight avoiding high stresses in areas to prone to develop pressure injuries, like ischial tuberosities (ITs). To assess support surfaces, the superficial pressure (Interface Pressure) are measuring. These measurements do not guarantee that internal tissue underlying to bony prominences (ITs) do not experience high stresses, however measurements in internal tissue are prohibitive. The present study estimates stresses and strains in underlying tissue of ITs applying Finite Element Method (FEM). A CAD model of pelvis was built from tomographic slices of a pelvis copy of a male subject, with 70 kg of weight and 1.70 m of high. The model was exported to finite element software COMSOL. The simulation conditions were: the bone and soft tissues were assumed linear and isotropic; load 450 N simulated the body trunk, and six cases were analyzed: healthy tissues; pressure injuries in internal tissue underlying to ITs; pressure injuries that affect all soft tissue without included skin; pressure injuries that affect all soft tissue included skin; and pressure injuries that affect skin and part of soft tissue. Maximum stress points in all cases are located below ITs, this fact is according to literature. The stresses in healthy tissues are lower than sides with pressure injuries, and stresses and strains of internal pressure injuries are higher than stresses and strains of external pressure injuries. The tendency of strains are to increase while tissue density decreases, it means the greater tissue damage, the greater strains. In tissue with 25% of damage, strains were 1.02 higher than healthy tissue. In otherwise, stresses are greater in internal pressure injuries, this fact is not observed in external pressure injuries, and however the stress value is decreased while tissue damage is increased. This analysis can be applied to design customized support surface for subject with spinal cord injury.