A pressure injury is a localized area of damage that occurs to the skin and/or the soft tissue lying beneath it, typically situated over a bony prominence. This damage is a result of intense or prolonged pressure, often combined with a shearing force, which limits blood flow to the affected area. The former terms “pressure ulcer” or “bedsore” have been replaced by “pressure injury” to reflect that tissue damage can occur even when the skin is still intact. Classifying these injuries is done by assessing the depth of the tissue damage, which guides medical professionals in their treatment approach and allows for standardized communication about the wound’s severity.
The Pressure Injury Staging Framework
Pressure injuries are categorized using a staging system developed by organizations like the National Pressure Injury Advisory Panel (NPIAP) to standardize assessment and guide care plans. This framework includes four numbered stages (1, 2, 3, and 4) and two additional classifications: Unstageable and Deep Tissue Injury (DTI). The stages represent a progression from the most superficial tissue damage to the deepest, full-thickness injuries.
The staging system provides a consistent method for documenting the extent of the wound. Stage 1 involves only intact skin, while Stage 2 involves partial-thickness skin loss. Stages 3 and 4 represent full-thickness tissue loss, signifying damage that extends through all layers of the skin and into underlying structures. The purpose of this framework is to clearly define the tissue layers involved, which directly influences the complexity of the required medical intervention.
Characteristics of a Stage 3 Injury
A Stage 3 pressure injury is defined by full-thickness skin loss, meaning the damage has completely eroded both the epidermis (outer layer) and the dermis (inner layer). The injury extends downward into the subcutaneous fat layer, or adipose tissue, which may be visible within the ulcer bed. This damage often presents as a deep, open ulcer that can resemble a crater on the skin’s surface.
The depth of a Stage 3 injury can vary significantly depending on the anatomical location of the wound. Areas of the body with substantial fat deposits, such as the buttocks, can develop deep Stage 3 injuries. However, the defining characteristic is that while subcutaneous fat is exposed, the damage does not extend through the underlying fascia to expose structures like muscle, tendon, ligament, or bone.
The edges of the wound may sometimes appear rolled, a condition known as epibole. Healthy, reddish granulation tissue may be present in the wound bed as the body attempts to heal. Necrotic tissue, which is dead or damaged tissue appearing as yellow, tan, or brown slough or black eschar, may also be visible. The presence of slough or eschar does not automatically change the stage, provided the depth of the tissue loss remains clearly visible.
Undermining or tunneling may also be observed in a Stage 3 injury, where tissue destruction occurs beneath the intact skin around the wound’s perimeter. Undermining refers to the erosion of tissue under the wound edges, while tunneling describes channels or tracts that extend away from the visible wound. These deeper extensions confirm the significant tissue loss associated with this stage.
Differentiating Stage 3 from Deeper Injuries
Distinguishing a Stage 3 injury from deeper classifications, primarily Stage 4 and Unstageable injuries, relies on identifying the deepest visible tissue layer. The line separating a Stage 3 from a Stage 4 injury is the involvement of deeper anatomical structures. In a Stage 3 injury, the deepest visible layer is adipose tissue, or subcutaneous fat.
A Stage 4 pressure injury is characterized by full-thickness skin and tissue loss that extends beyond the fat layer. It exposes or makes directly palpable the underlying fascia, muscle, tendon, ligament, cartilage, or bone. The presence of any of these deeper structures automatically classifies the wound as Stage 4. The extent of tissue loss in a Stage 4 injury is significantly greater and carries a higher risk of complications, such as bone infection.
An Unstageable pressure injury also involves full-thickness skin and tissue loss, but the true depth cannot be determined because the wound bed is covered by a significant amount of slough or eschar. This necrotic tissue completely obscures the base of the injury, making it impossible for a clinician to confirm whether the damage stops at the subcutaneous fat (Stage 3) or extends to bone or muscle (Stage 4). Once this obscuring material is removed through debridement, the injury can then be accurately staged as either a Stage 3 or Stage 4.