Deep tissue injury: how deep is our understanding?

Deep pressure ulcers, necessarily involving deep tissue injury (DTI), arise in the muscle layers adjacent to bony prominences because of sustained loading. They represent a serious type of pressure ulcer because they start in underlying tissues and are often not visible until they reach an advanced stage, at which time treatment becomes problematic. Underlying mechanisms of DTI require further investigation if appropriate preventive measures are to be determined. The present commentary illustrates a hierarchic research approach selected to study these mechanisms. To differentiate between the individual roles of deformation and ischemia in the onset of skeletal muscle damage, 2 complementary approaches have been selected. In an in vivo animal model, the effects of ischemia combined with deformation and ischemia per se were studied. An in vitro muscle model was used to study the separate effects of deformation and several aspects of ischemia, including hypoxia, glucose depletion, and tissue acidification, in more detail. Based on the results of both models a sequence of events leading to cell necrosis is proposed. Deformation levels exceeding a threshold value can result in rapid tissue damage that may persist, whereas ischemia has a more gradual effect as a result of glucose depletion and tissue acidification.