A wound is defined as a physical injury where the skin or mucous membrane is torn, pierced, cut, or otherwise broken. The process of wound healing is complex and involves inflammatory, vascular, connective tissue and epithelial cells working together over a period of time. To better understand wound healing we need to learn more about the different types of wounds and factors involved in their healing.
Classification of wounds
There are many different ways in which wounds can be classified. In many cases a wound may consist of a combination of the different classifications.
|1. Wound thickness|
|Superficial||Involves only the epidermis and the upper dermis|
|Partial thickness||Involves skin loss up to the lower dermis|
|Full thickness||Involves skin and subcutaneous tissue|
|Deep and complicated||Involves penetration into natural cavities, an organ or tissue|
|2. Wound complexity|
|Simple||Affecting only one organ or tissue|
|Combined||Affecting multiple organs and/or tissue|
|3. Wound age|
|Fresh||Up to 8 hours from the time of injury|
|Old||After 8 hours from the time of injury|
|4. Wound origin|
|Superficial||Breaking the skin’s surface from scratching, rubbing, picking, or a graze from falling|
|Incised||Usually as a result of surgical intervention|
|Crush||Made with a heavy blow of a cutting tool, e.g. hatchet, sword|
|Lacerated||Fragments of tissue torn away with a sharp-edged object|
|Stab||Made with a pointed tool or weapon|
|Contused||Injury to tissue under the skin's surface, most common type of wound seen in traffic accidents|
|Secondary||Wounds originating from primary diseases, e.g. diabetic ulcers, pressure ulcers, venous ulcers|
|Other||Bullet wound, bite wound, poisoned wound|
The process of wound healing involves three overlapping phases:
- Inflammation – involves scab formation and infiltration of damaged tissue by white blood cells. These are responsible for removing dead tissue and ingesting bacteria.
- Proliferation – involves development of granulation tissue, contraction of the wound and growth of epithelial cells under the dried scab
- Maturation – wound becomes less vascular and is strengthened by the rearrangement of collagen fibres.
The rate at which a wound heals is dependent on a number of factors. These factors need to be considered before deciding on the method(s) used to treat a wound. Factors to consider include:
- Position and size of the wound
- Tissue type (e.g. sloughy, necrotic, granulating)
- Amount of exudate
- Presence or absence of infection
- Presence or absence of pain
Wounds heal fastest if they are attended to as quickly as possible after injury. The aim should be to dress or close the wound using appropriate methods to keep it free from infection and to create an environment that promotes healing.
Methods of wound healing
In recent times there has been much development in the field of wound management. To minimise scar formation and to accelerate healing time, different wound coverings and different techniques of skin substitution have been introduced.
Wound covering can be broken down into two categories:
Permanent coverings – autografts
An autograft is when a layer of epidermis and dermis is taken from healthy skin areas of the patient and grafted onto the wounded area. This is the optimum wound cover but it has the drawback of creating a second wound (donor wound) on the patient which now also needs to be managed. This is the method of choice to cover large surface wounds, e.g. large burns.
Temporary coverings include allografts (e.g. de-epidermised cadaver skin and in-vitro cultured epidermal sheets), xenografts (e.g. pig skin grafting), and synthetic dressings. These coverings are temporary because of their synthetic or chemical components, limited adhesion to the wound surface, and foreign body character.
Synthetic wound dressings have come a long way from the days of traditional dressings (e.g. gauze-based products) and paste bandages (e.g. zinc paste). In the mid 1980s the use of polyurethane foams and hydrocolloids as wound dressings was the beginning of the discovery of a vast array of compounds and materials that are now available for dressing wounds. For detailed description of wound dressings see synthetic wound dressings.