A non-linear contact FE model to evaluate pressure ulcer on buttock-thigh under sitting

Pressure ulcer (PU) is one of the most common but serious medical complications experienced by people who rely on wheelchairs. Many previous finite element (FE) models related to buttock ignored the complexity including the anatomical geometry, non-linear property between skin and cushion and real physiological loading. In this investigation, a three-dimensional (3D) comprehensive FE model derived from MRI images under sitting was constructed to evaluate PU. Contact property between skin and cushion and physiological loading were considered in the model. The result shows that high pressure of 86-180 kPa in muscle under ischial tuberosity (IT) was predicted in our investigation, bigger than that of 50-80 kPa in skin and that of 40-50 kPa in fat. While differing from other literatures, the von-Mises stress of 80-120 kPa in skin was bigger than that of 10-30 kPa in fat and that of 30-50 kPa in muscle. The maximum frictional shear stress contributing to superficial pressure ulcer in anterior-posterior direction occurs just beneath the IT with the range of 3.9-6.5 kPa. In conclusion, the non-linear contact FE model proves valid in predicting mechanical response of superficial and internal tissues under sitting.