Stages of wound healing

Overview

Any cut or opening in the skin can be termed a wound. Wounds can result from a fall, accident, or trauma. A cut in the skin generated from a surgical or medical procedure is also classified as a wound. In general, wounds can be classified into five types which include cuts, burns, scrapes, puncture wounds, and pressure sores. The surface of the wound can be smooth or jagged depending on the circumstances. Deep wounds can also affect the muscles, blood vessels, ligaments, tendons, and bones that lie below the skin. Minor wounds can get healed easily while major wounds need special care to prevent the chances of an infection. While most of us do not pay much attention to the healing of minor wounds, the body has a natural mechanism to deal with wounds and it is a complex one.

The primary function of the human skin is to protect against mechanical impacts and pressure, variations in temperature, micro-organisms, and various other external situations. The two main layers of the skin are the epidermis and the dermis and generally the wounds which affect these two layers are healed quickly. A deeper wound can be serious and demand more attention and proper medical care. The healing of wounds is an organized process and involves four major steps which are hemostasis, inflammation, proliferation, and maturation. Some wounds are chronic and they either do not heal or heal slowly or heal but tend to recur. Such wounds can result from various conditions like trauma, burns, skin cancers, severe infection, or underlying medical situations such as diabetes. These types of wounds need special attention and care along with longer periods for healing.

Classification of wounds

There is no standard method of wound classification but they are often categorized based on the management and final healing. The various factors that affect their classification are aetiology, location, type of injury or symptoms, and wound depth and tissue loss. In general, wounds can be classified into three types.

• Superficial which involves only the loss of the epidermis
• Partial-thickness wounds involve the loss of the epidermis and the dermis.
• Full-thickness wounds involve the dermis, subcutaneous fat, and sometimes even the bone.

In terms of how they have been caused, open wounds can be classified into the following main categories. Depending on the nature of the wound, the type of treatment required will vary.

Abrasion

An abrasion occurs when the skin gets rubbed or scrapes against a rough or hard surface. The outer surface of the skin is peeled away but there is no major bleeding as the blood vessels are not damaged. Even then, such a wound needs to be cleaned to avoid an infection.

Laceration

A laceration is a deep cut or tearing of the skin that is generally caused by a sharp object or an edge. Accidents with knives, tools, and machinery are the most frequent causes of lacerations. In the case of deep lacerations that penetrate through the layers of skin, bleeding can be extensive. These wounds need more care to stop the bleeding.

Puncture

A puncture is a small hole on the skin that is caused by a long, sharp object. An injury from a nail, needle, or bullet injury can be classified as a puncture wound. While such a wound may not bleed much, it can be deep enough to damage internal layers and organs. Even for a small puncture wound, a tetanus shot is needed to prevent any chances of an infection.

Avulsion

An avulsion is a serious kind of wound that happens when there is a partial or complete tearing away of the skin and the underlying tissue. Avulsions usually occur during violent accidents that put heavy stress on the body and also result from explosions and gunshots. They can cause a rapid loss of blood and can be life-threatening at times.

The stages of wound healing

The process of wound healing is another wonderful example of how the various mechanisms of our body work together to promote repair and regeneration. The process involves four different stages that are interlinked and are often termed as the “cascade of healing”. The process is complex and fragile and any break in the stages can lead to the formation of chronic wounds. The process is also dependent on various factors like moisture, infection, age, nutritional status, and the overall health of the patient. When the right healing environment is established, healing can be fast and effective. The four stages of wound healing are discussed in detail below.

The haemostasis phase

Haemostasis is the first phase of healing and its main objective is to stop the bleeding. When any blood leaks out of the body, the first step that comes into play is the process of clotting. This is a kind of a dam that forms as the platelets in the blood stick together to seal the opening of the torn blood vessels. The platelets work together with a protein called collagen and the whole process is controlled by an enzyme called thrombin. The threads of a compound called fibrin are formed which starts to adhere within the first sixty seconds of a wound formation. As the fibrin forms a mesh, blood gets transformed from liquid form to a gel form through the pro-coagulants and the release of another enzyme called prothrombin. This is termed the process of coagulation and it reinforces the mesh structure of the fibrin. Finally, a clot or a thrombus is formed that keeps the blood cells trapped in the wound area. While the thrombus plays an important role in sealing the wound and reducing blood discharge, it can cause serious problems in case it detaches and goes through the circulatory system. Such an element in the blood vessel can cause a stroke, pulmonary embolism, or a heart attack.

The defensive or the inflammatory phase

The second phase is called the defensive or the inflammatory phase as it focuses on destroying bacteria and removing debris. This stage essentially prepares the wound bed for the growth of new tissue. The injured blood vessels also leak some substances that cause inflammation. A type of white blood cell called neutrophils plays a significant role by entering the wound to destroy the bacteria and remove debris. These cells often reach their peak concentration within 24 and 48 hours after injury and then they reduce in number after three days. As the neutrophils leave the stage, specialized cells called macrophages arrive to continue clearing the debris. These cells also secrete special growth factors and proteins that attract other immune system cells to the wound and facilitate the process of tissue repair. This phase usually lasts for four to six days and is often associated with oedema, reddening of the skin, heat generation, and pain. The inflammation associated with this stage is natural and generally subsides within a few days.

The proliferative phase

The third stage starts when the wound is cleaned and here the main focus is on the filling and covering of the wound. The wound margins are gradually reduced until the wound is filled up. A special shiny, deep red granulation tissue fills up the wound bed and the new blood vessels are formed. The healthy granulation tissue is pink or red and uneven in texture. The myofibroblast cells cause the wound margins to contract and they are gradually pulled towards the centre of the wound. Finally, the new epithelial cells arise from the wound bed and the margins, until the entire wound is covered. The process is enhanced when the wound is kept slightly moist. The entire proliferative stage can last anywhere from 4 to 24 days depending on the nature of the wound.

The maturation phase

This is the final stage of healing when the new tissue gains strength and becomes more flexible. The collagen is restructured as the fibres reorganise. The collagen pattern changes from type III to type I and the wound fully closes with time. The cells that were used in the process of healing but are no longer needed are removed by the process of apoptosis.  When the collagen fibres come into play, they are thick and the wound surface is uneven. Gradually the fibres come together, absorb water, and cross-link with each other. This process reduces the amount of scar tissue and makes the skin stronger in terms of tensile strength. Even though there is an overall increase in the tensile strength of the tissue as it matures, it is only around 80 percent of that of uninjured skin. This final process starts around 21 days after an injury and can continue for a year or more.

The time taken for wounds to heal

As mentioned earlier, the healing process depends on a number of factors and the time taken also depends on the nature of the wound. An open wound usually takes longer to heal than a closed wound. In general, after about a period of 3 months, most wounds are repaired. A large or deep cut will heal faster if sutures are applied to it. This helps as the total area that the body has to rebuild becomes smaller. This is the reason that surgical wounds heal faster than wounds of other kinds. Wounds will also heal faster or better when they are kept covered and a bandage also keeps the wound cleaner. Patients with specific medical conditions can find their wounds taking a long time to heal properly. These conditions include diabetes, obesity, high blood pressure (hypertension), and vascular disease. In case a wound gets infected before it is healed properly, the healing process can take a much longer time than normal. Any infection that causes pain or inflammation needs to be treated seriously. Some signs of a wound becoming infected are listed below.

• A slow rate of healing or no healing at all
• Prolonged swelling and redness around the area
• Pain or tenderness
• It can get hot or warm to touch
• The wound can ooze pus or liquid

There are some serious conditions that can result from open wounds in rare cases. These can further delay the process of healing. Such conditions include the following.

Lockjaw

This infection is caused by bacteria that also cause tetanus. It can result in muscle contractions in the jaw and neck region.

Necrotizing fasciitis

This is a severe infection of the soft tissue below the skin. It is caused by a range of bacteria including Clostridium and Streptococcus that can lead to tissue loss and even sepsis.

Cellulitis

This is a bacterial infection of the skin that is not in immediate contact with the wound. It can spread easily into other areas of the skin.

Factors that prevent wound healing

The following factors reduce the rate of wound healing and should be avoided.

• Dead skin and foreign materials interfere with the healing process and hence they should be cleaned. Cleaning should be done gently without causing any further damage.
• Open wounds often develop into bacterial infections. In such a case, the body will fight the infection rather than proceed with healing the wound.
• Continuous bleeding will keep the wound edges apart and prevent wound healing.
• A patient who remains immobile for a long period is at risk of bedsores because of constant pressure and friction on certain areas of the skin.
• The body needs nutrients like vitamin C, zinc, copper, and protein to heal a wound and for the formation of collagen. An improper diet and poor food choices will deprive it of the same and interrupt healing.
• Wounds in elderly people take more time to heal.
• Some drugs or treatments can interfere with the body’s inherent healing process.
• Cigarette smoking impairs the healing mechanism and also increases the risk of further complications.
• Dryness of the skin can reduce healing and some wounds like ulcers, which are exposed to the air may not heal. As said before, a moist environment is a need for the effective functioning of the various cells involved in the healing process.

Conclusion

The process of wound healing happens in multiple stages and takes time. So, even though the wound can appear red, swollen, and watery in the beginning, this may very well be a part of the healing process. A scar from a wound may look uneven at first but it generally gets flatter and duller in colour. With the right care, most wounds will heal completely without a scar. However, larger wounds will need some extra care and they are likely to leave a scar.

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