A finite element approach for analyzing the effect of cushion type and thickness on pressure ulcer

• Numerical models to estimate maximum stress at ischial tuberosity due to immobilized continuous sitting are presented.
• Both rigid and soft cushion seats are analyzed using finite element method.
• Variation of stress distribution at ischial tuberosity over time is presented.
• Effect of thickness of seat and postural change on stress distribution is investigated.

Immobilization or continuous sitting with a constant posture for a long time in office environment causes sub-dermal tissue damage. Tissue damage occurs because of continuous prolonged compression of buttock soft tissue under body weight. It is treated as the end result of cell death or tissue deformation which ultimately gives rise to pressure ulcer. Although the sub-dermal tissue refers to the tissue beneath the skin, it is the tissue just below the bony portion undergoes maximum deformation because the muscle endures a continuous high stress. In this work, a simple but practical numerical approach has been proposed to estimate the maximum stress beneath the bony structure (ischial tuberosity). The model is validated with experimental data from the literature. Effect of properties of cushion material, loading angle and thickness of cushion has been analyzed. The cushion properties and thickness that can reduce maximum stress at ischial tuberosity have been demonstrated. The effect of sitting posture on maximum stress at ischial tuberosity has also been shown.Relevance to industryThe study can possibly help the practitioners to select type of cushion and its thickness that can reduce pressure ulcer during prolonged sitting. The simplified but practical model presented in this paper can provide a platform to study the behaviour of different type of cushion material and thickness reducing expensive experimental burden.