Deep tissue injuries can have the same outward appearance as decubitus ulcers, but the underlying etiology is different. These injuries happen and progress quickly.
The mechanism of this injury is pressure to the skin and soft tissue, within a short period of time, that compromises tissue perfusion and results in ischemia and damage to the deeper subcutaneous tissues.
The initial injury is not visible on the surface of the skin and only manifests later as the underlying tissue starts to necrose, first forming what appears to be a bruise before progressing to an external/visible skin wound.
This type of wound evolves upward towards the skin as well as deeper, so once the external wound becomes apparent, it is frequently already a deep injury often with the appearance of a Stage 3–4 decubitus ulcer.