The classification of wounds is based on severity, morphology, thickness and aetiology.
Wounds are generally classified as wounds without tissue loss (e.g., surgery) and wounds with tissue loss. Classification based on severity considers the amount of tissue damage, involvement of muscle, bone, nerve and whether infection is present.
These include burn and ulcer wounds, pressure sores, wounds caused as a result of trauma, abrasions, and iatrogenic wounds such as skin graft donor sites and dermabrasions. Wounds are also classified by the layers involved, superficial wounds involve only the epidermis, partial-thickness wounds involve only the epidermis and dermis, and full-thickness wounds involve the subcutaneous fat or deeper tissue;
these are based on the morphology of the wound. Wounds are also classified based on the cause of wound formation; thus classification by aetiology considers wounds such as: surgical, traumatic, burn, pressure, venous and diabetic ulcers, radiation, keloid and hypertrophic scars, amputation and immunosuppressive. Acute wounds are those which heal normally, however, some wounds do not heal even after 6 weeks and are termed chronic wounds. These wounds are also classified as black − which contains necrotic tissue, yellow − which requires autolytic debridement and moist wound healing, and red − granulating wounds that require moist wound healing.
Surgical wounds can be classified according to the degree of contamination, i.e., clean, clean-contaminated, contaminated and infected, as per the USA National Research Council. Clean wounds are those made under sterile conditions where there are no organisms present; these wounds are likely to heal without any complications. Clean- contaminated wounds are surgical wounds with a minor break in aseptic technique, e.g., elective opening of respiratory, gastrointestinal, biliary or genitourinary tract with minimal spillage (appendectomy, cholecystectomy and so on). Contaminated wounds occur via accidental injury and contain pathogens and foreign bodies in the wound. Old traumatic wounds with existing infection, or organisms which are present before surgery, are termed dirty wounds; these wounds are characterised by the presence of pus.
Wound-care professionals have also classified wounds based on aetiology. The four different wound aetiology classifications are pressure ulcers, neuropathic ulcers, vascular ulcers (arterial and venous) and burns. Pressure ulcers are classified into six stages as per the National Pressure Ulcer Advisory Panel. A pressure ulcer is defined as a localised injury to the skin and/or underlying tissue, usually over a bony prominence, as a result of pressure or pressure in combination with shear. The different categories or stages of pressure ulcer are:
• Category/stage I: nonblanchable erythema.
• Category/stage II: partial-thickness skin loss.
• Category/stage III: full-thickness skin loss.
• Category/stage IV: full-thickness tissue loss.
• Unstageable/unclassified: full-thickness skin or tissue loss with unknown depth.
• Suspected deep tissue injury of unknown depth.
Intact skin with nonblanchable redness of a localised area, usually over a bony prominence, accompanied by pain and is firm, soft, warmer or cooler as compared to the adjacent tissue is categorised as category I. Partial-thickness loss of the dermis with a red pink wound bed, without slough is categorised as category II.
Full-thickness tissue loss with visible subcutaneous fat is classed as category III.
Category IV has full-thickness tissue loss with exposed bone, tendon or muscle.
In addition to these four stages some ulcers exhibiting full-thickness skin or tissue loss are unclassified, because the actual depth of the ulcer is completely obscured by slough and/or eschar in the wound bed. There is yet another category for pressure ulcer, i.e., suspected deep tissue injury where the depth of the ulcer is unknown. This could be a purple or maroon localised area of discoloured intact skin or blood-filled blister due to damage of the underlying soft tissue from pressure and/or shear. Neuropathic ulcers are classified according to the Wagner Ulcer Grade Classification and the University of Texas, San Antonio Classification. Wounds are graded by the depth of the wound and the presence of infection, and are denoted by five numeric grades which begin with pre-ulcerative lesions, healed ulcers, or the presence of bony deformity, and conclude with gangrene of foot requiring amputation. According to the University of Texas classification, there are four numeric grades which start with pre-ulcerative lesions and end with wound penetrating to the bone and joint. Burns are classified mainly by the depth of injury. The five categories are:
• Superficial.
• Superficial partial-thickness skin loss.
• Deep partial-thickness skin loss.
• Full-thickness dermal loss.
• Subdermal extending into muscle.
Wounds can be acute or chronic with additional subclassifications. Acute wounds include surgical incisions and traumatic injuries, such as lacerations, abrasions, avulsion, penetrations or bits and burn injuries. Generally, acute wounds are classified into one of eight categories: 1) abrasions occur when the skin is rubbed away by friction; 2) avulsion occurs when an entire structure or part of it is forcibly pulled away, for example, explosions, gunshots or animal bites and so on; 3) contusions,
often called bruises, occur as a result of forceful trauma that injures an internal structure without a skin breach; 4) crush wounds are those that split or tear the skin or underlying structure by means of heavy objects falling onto the body; 5) cuts can be caused by sharp instruments that are minor to major, for example, a surgical incision; 6) laceration can be caused by tears produced by tremendous force acting against the body either from inside or by an external source, such as a punch; 7) missile wounds are caused by a fast-moving object piercing the body, typically a bullet; and 8) punctures are produced by sharp objects, such as a knife or broken glass, which cause narrow deep wounds. Chronic wounds are generally classified into one of three types: 1) pressure ulcers, also known as bedsores, are caused by prolonged unrelieved pressure to an area of the body; these wounds are typically found with individuals who are bedridden or with limited mobility for a long duration; 2) arterial and venous ulcers occur due to dysfunction of the valves in the veins causing reduced blood flow in certain areas of the body, mainly in the lower limbs; the impaired blood flow causes chronic inflammation and when this area is injured the wound is unable to heal by itself and becomes chronic; and 3) a diabetic ulcer is another major form of chronic wound; a diabetic person has decreased nerve function and impaired pain sensing along with a poor immune response.
Wounds can also be categorised depending on their depth. If only a portion of the epidermis or complete depth of the epidermis is injured, it regenerates to the pre-injury state and these wounds are termed partial-thickness wounds. Healing occurs mainly via epithelialization and examples include first-degree burns and abrasions. If the injury extends deep into the dermis, repair occurs rather than regeneration and these wounds are termed full-thickness wounds, as shown in Figure 5.1. Deep wounds are those that extend through the dermis and into deeper structures such as the subcutaneous fat. Wounds deeper than 4 mm are generally termed full-thickness wounds and heal by second intention. The other most common method for classification of a wound is identification of the predominant tissue types present at the wound bed, i.e., black wound, yellow wound and red wound. A black wound is a wound covered with black necrotic dried blood and skin products; a yellow wound shows signs of slough and this signals possible infection, whilst a red wound indicates that the wound is clean and the granulation process is healing the wound.
Epidermis layer
Basement membrane Superficial wound Partial-thickness wound Full-thickness wound
Dermis layer
Hypodermis layer
Figure 5.1 Categorisation of wounds based on depth