Pressure ulcer risk: the effect of anatomical features on interface pressure and tissue deformation in people with spinal cord injury

Pressure ulcers are one of the most common secondary complications for people with spinal cord injury, and add $10 billion annually to healthcare costs in the US. They are the most frequently seen preventable hospital acquired condition. Recent pressure ulcer research has added examination of anatomical risk factors, mainly fat and muscle characteristics, to the many previously identified risk factors. Translation of the new anatomical-based risk assessment theories is contingent on development of clinical techniques for measurement and better understanding of relationships with known factors, which has slowed the integration of this research into clinical settings. This study was designed to help bridge this gap between lab and clinic, by examining how anatomical features affect both tissue deformation and interface pressure. Six participants – two control and four with spinal cord injury – underwent MRI imaging while seated on a variety of seat cushions and in an unloaded condition, as well as pressure mapping. Three dimensional models of the tissue were created from the images. Significant anatomical differences were observed between the two groups. People with SCI lack muscle under the ischial tuberosity when sitting. The results suggest that tissue thickness was the anatomical feature most indicative of pressure ulcer risk. Greater unloaded thickness was associated with lower interface pressure and less change in tissue volume under seated loads, signifying a decrease in pressure ulcer risk. Higher deformation asymmetry – an imbalance between the change in tissue volume from one side of the buttocks to the other – also suggested increased pressure ulcer risk. Deformation asymmetry is particularly important because it can be partially corrected by adjusting sitting posture. These important characteristics should be used to direct further efforts to implement a more personalized risk model based upon the anatomy of the tissues at risk of breaking down.