An air-cell-based cushion for pressure ulcer protection remarkably reduces tissue stresses in the seated buttocks with respect to foams: Finite element studies

A sitting-acquired pressure ulcer (PU) is a common injury in wheelchair-bound patients. Preventative measures for the post spinal cord injury (SCI) population include prescription of a supportive thick cushion on the wheelchair, in order to better distribute loads between the buttocks and support surface (which are quantifiable using interface pressure measurements), and potentially, to minimize internal soft tissue loads (which are typically unknown). Information about the biomechanical efficacy of commercially-available structured cushion designs such as air-cell-based (ACB) cushions, gel, and honeycomb-like cushions is sparse. Considering the importance of such evaluations to patient safety and quality of life, we studied the biomechanical performances of an ACB cushion in comparison to standard, flat foam cushions with different stiffness properties. Using a set of finite element (FE) model variants, we determined the mechanical stresses in muscle, fat, and skin tissues under the ischial tuberosities during sitting. Tissue stress analyses were conducted in a reference SCI anatomy, incorporating pathoanatomical and pathophysiological changes associated with chronic SCI, including bone shape adaptation, muscle atrophy, and spasms. We found up to 57% greater immersion and 4 orders-of-magnitude lower muscle, fat, and skin tissue stresses for the ACB cushion. We also found the ACB cushion provides better protection against the aforementioned bone shape adaptation, muscle atrophy, and spasms. Hence, theoretically, the use of a suitable ACB cushion should provide longer safe sitting times for SCI patients with respect to standard foam cushions.