Ultrasound elastography reveals relations between body posture and soft tissues stiffness which are relevant to the etiology of sitting-acquired pressure ulcers.

Sitting-acquired pressure ulcers (PUs) are common in wheelchair users. Such PUs are often serious and may involve a deep tissue injury (DTI). Investigating the mechanical properties of the tissues susceptible to DTIs may help in guiding prevention and early detection of PUs. In this study, ultrasound shear wave elastography (SWE) was used to measure normative mechanical properties of the soft tissues of the buttocks, i.e. skeletal muscle and subcutaneous fat, under the ischial tuberosities, in a convenience sample of healthy adults without weight bearing and with weight-bearing of different times. We compared the stiffness properties of these soft tissues between the lying prone and sitting postures, to determine if there are detectable property changes which may be associated with the type of posture. We hypothesized that muscle contractions and three-dimensional tissue configurations associated with the posture may influence the measured tissue stiffnesses. Our results have shown that indeed, SWE values differed significantly across postures, but not over time in a specific posture or for the right versus left sides of the body. We have therefore demonstrated that soft tissue stiffness increases under sitting with weight bearing and may contribute to increasing the potential PU risk in sitting compared to lying prone, given the stiffer behavior of tissues observed in sitting postures.