Lag phase

The lag phase is the delay of 2–3 days that elapses before fibroblasts begin to manufacture collagen to support the wound. It is characterized by an inflammatory response to injury, during which capillary permeability increases and a protein-rich exudate accumulates. It is from this exudate that collagen is later synthesized. Inflammatory cells migrate into the area, dead tissue is removed by macrophages, and capillaries at the wound edges begin to proliferate.

Incremental phase

During the incremental or proliferative phase, there is progressive collagen synthesis by fibroblasts and a corresponding increase in tensile strength. Increased collagen turnover in areas remote from the wound suggests that there may also be a systemic stimulus for fibroblast activity. Collagen synthesis increases over a period of about 3 weeks, during which the gain in tensile strength accelerates. Old collagen undergoes lysis and new collagen is laid down.

Plateau or maturation phase

After 3 weeks, the gain in tensile strength levels off as the rate of collagen breakdown first approaches and then temporarily surpasses its synthesis. Excess collagen is removed during this final clearing-up process and the number of fibroblasts and inflammatory cells declines. Orientation of collagen fibres in the direction of local mechanical forces increases tensile strength for some 6 months. However, skin and fascia usually recover only 80% of their original tensile strength.

At the time of suture removal, the edges of the newly healed wound should be directly apposed and flat. Thereafter, for up to 3 months, the scar may become progressively raised, red and thickened. It can then remain static for a further 3 months, before slowly improving to become narrow, flat and pale. These changes vary with age, race, the direction of scar and the degree of dermal damage.

In children, scars take longer to resolve, whereas in the elderly they tend to mature and fade very quickly.

Hypertrophic scars

This is an exaggeration of the normal maturation process. Such wounds are very raised, red and firm, but never continue to worsen after 6 months. They are particularly common in children and after deep dermal burns. Unless under tension, they eventually resolve, often after several years. Resolution can be hastened by elastic pressure garments, steroid injections or the application of silicone gel. These scars should not be excised.

Keloids

These are similar to hypertrophic scars, except that they continue to enlarge after 6 months and invade neighbouring uninvolved skin. They are most likely to occur across the upper chest, shoulders and earlobes, and are common in black patients. They are difficult to treat successfully. If the measures described above fail, intralesional excision followed immediately by low-dose radiotherapy is sometimes considered.

Epidermis

Epithelium heals by regeneration and not by scar formation. Epithelial cells at the edge of the wound lose their adhesion to each other and migrate across the wound until they meet cells from the other side. As they migrate, they are replaced by new cells formed by the division of basal cells near the wound edge. The cells that have migrated undergo mitosis and the new epithelium thickens, eventually forming normal epithelial cover for the scar produced by the dermis.

Primary and secondary intention

Wounds may heal by primary intention if the edges are closely approximated: for example, by accurate suturing. Epithelial cover is quickly achieved and healing produces a fine scar (Fig. 18.4). If the wound edges are not apposed, the defect fills with granulation tissue and the restoration of epidermal continuity takes much longer. The advance of epithelial cells across the denuded area may be hindered by infection. This is known as healing by secondary intention and usually results in delayed healing, excessive fibrosis and an ugly scar (Fig. 18.5). If a wound has begun to heal by secondary intention, it may still be possible to speed healing by excising the wound edges and bringing them into apposition, or by covering the defect with a skin graft.

Fig. 18.4 Wound healing.

A Healing by primary intention. B Healing by secondary intention, showing shrinkage of the wound.

Fig. 18.5 Healing by secondary intention.

Blood supply

Wounds in ischaemic tissue heal slowly or not at all. They are prone to infection and frequently break down. When this occurs, the wound may not be able to sustain the metabolic demands of healing by second intention. Arterial oxygen tension (PaO₂) is a key determinant of the rate of collagen synthesis. Anaemia may not affect healing if the patient has a normal blood volume and arterial oxygen tension. Poor surgical technique, such as crushing tissue with forceps, approximating wound edges under tension and tying sutures too tightly, can make well vascularized tissue ischaemic and lead to wound breakdown.

Infection

The general risks of wound infection depend upon age, the presence of intercurrent infection, steroid administration, diabetes mellitus, disordered nutrition, and cardiovascular and respiratory disease. Local factors are also important. Bacterial contamination can be minimized by careful skin preparation and aseptic technique, but some wounds are more likely to be contaminated than others. Bacteria may enter wounds from the atmosphere, from internal foci of sepsis or from the lumen of transected organs. In some cases, contamination occurs in the postoperative period. Provided contamination is not gross and local blood supply is good, natural defences are usually able to prevent and contain overt infection. Devitalized tissues, haematomas and the presence of foreign material such as sutures and prostheses favour bacterial survival and growth. Common infecting organisms are staphylococci, streptococci, coliforms and anaerobes. Overcrowding of wards and excessive use of operating theatres increase the bacterial population of the atmosphere and hence the risk of wound infection. The failure of medical and nursing staff to wash their hands before and after touching and examining each patient is perhaps the greatest source of cross-contamination.

When wound contamination is anticipated, topical antibacterial chemicals or topical and systemic antibiotics can be used prophylactically. For example, a single dose of systemic antibiotic is normally used to reduce the risk of infection during gastrointestinal surgery and when prosthetic material (hip joint, cardiac valves, arterial bypass) is being inserted. In acute traumatic wounds, tetanus prophylaxis is routine, but antibiotics are not normally necessary provided prompt and thorough surgical treatment is undertaken. However, if there has been a delay in the treatment of such a wound, antibiotic prophylaxis may be necessary.

Age

Wounds in the elderly may heal poorly because of impaired blood supply, poor nutritional status or intercurrent disease. However, as mentioned above, they tend to form ‘good’ scars.

Site of wound

Surgical incisions placed in the lines of least tissue tension are subject to minimal distraction and should heal promptly, leaving a fine scar. On the face, these lines run at right angles to the direction of underlying muscles and form the lines of facial expression.

Nutritional status

Malnutrition has to be severe before healing is affected. Protein availability is most important, and wound dehiscence and infection are common when the serum albumin is low. Healing problems should be anticipated if recent weight loss exceeds 20%. Vitamin C is essential for proline hydroxylation and collagen synthesis. The number of fibroblasts is not reduced in scorbutic states. Zinc is a co-factor for important enzymes involved in healing, and its deficiency retards healing. Supplements of ascorbic acid and zinc are effective in patients with known deficiencies, but do not improve healing in normal subjects.

Intercurrent disease

Healing may be affected by the disease itself or by its treatment. Cachectic patients with severe malnutrition (as seen in advanced cancer) have marked impairment of healing. Diabetes mellitus impairs healing by reducing tissue resistance to infection and by causing peripheral vascular insufficiency and neuropathy. Haemorrhagic diatheses increase the risk of haematoma formation and wound infection. Obstructive airway disease lowers arterial PO₂ and so affects healing. Abdominal wound dehiscence is more common in patients with respiratory disease because of the strain put on the wound during coughing. Corticosteroid therapy reduces the inflammatory response, impairs collagen synthesis and decreases resistance to infection. The effect of steroids on wound healing is most marked if they are given within 3 days of injury. Immunosuppressive therapy and chemotherapy impair healing by reducing resistance to infection. As radiotherapy greatly reduces the vascularity of the tissues, the healing of wounds in irradiated areas is often impaired.

Surgical technique

Where possible, skin incisions are placed in the line of least tissue tension. Aseptic technique, gentle handling and accurate apposition of wound edges favour healing by first intention. Dead spaces must be avoided, as the accumulation of blood and exudate encourage infection. Correct suturing of the deeper layers avoids dead space and often allows the skin edges to fall together without tension, so that superficial sutures or adhesive tape can achieve skin apposition. Drains should be used in contaminated wounds and those where exudate is expected. Drains may be connected to a suction apparatus or allowed to empty by gravity. The drain site is a potential portal of entry for infection and drains should be removed as soon as possible, especially when prosthetic material has been implanted.

Choice of suture and suture materials

Foreign material in the tissues predisposes to infection. The finest sutures that will hold the wound edges together should be used. Whereas 5/0 or 6/0 sutures are appropriate for the face, stronger ones (3/0 or 4/0) are needed for incisions near joints and still stronger ones for the abdominal wall. The suture should be strong enough to support the wound until tensile strength has recovered sufficiently to prevent breakdown. Absorbable materials are preferred for buried layers.

Classification

Surgical procedures can be classified according to the likelihood of contamination and wound infection as ‘clean’, ‘clean-contaminated’ and ‘contaminated’:

Antibiotic prophylaxis is appropriate for the latter two types of operation.

Clinical features

Wound infection usually becomes evident 3–4 days after surgery. The first signs are usually superficial cellulitis around the margins of the wound, or swelling of the wound with some serous discharge from between the sutures. Fluctuation is occasionally elicited when there is an abscess or liquefying haematoma. Crepitus may be present if gas-forming organisms are involved. In some cases of deep infection, there are no local signs, although the patient may have pyrexia and increased wound tenderness. Systemic upset is variable, usually amounting to only moderate pyrexia and leucocytosis. Toxaemia, bacteraemia and septicaemia can complicate serious wound infection, especially where there is an accumulation of pus. The differential diagnosis includes other causes of postoperative pyrexia, wound haematoma and wound dehiscence. Wound haematoma may result from reactive bleeding during the first 24–48 hours after an operation. It causes swelling and discomfort, but only minimal pyrexia and few systemic signs.

Prevention

The risk of wound infection is reduced by careful patient preparation, the prophylactic use of antibiotics in high-risk patients, and meticulous attention to good operating theatre techniques. Severely contaminated wounds are sometimes best closed by delayed primary suture; most gunshot wounds are treated in this way. Skin sutures may be inserted at this time but are not tied for several days, by which time it should be clear that infection has been avoided. Antibiotic therapy is essential for grossly contaminated wounds. The aim is to achieve high tissue concentrations as soon as possible. The choice of antibiotic is determined by the nature of the infection. Topical agents such as povidone-iodine may also be used to combat infection in contaminated wounds. Radical excision of the wound margins, thorough mechanical cleansing and delayed suture may also be required.

Management

A wound swab or specimen of pus is routinely sent for bacteriological culture and sensitivity determination. In urgent cases, a Gram stain may be useful. The state of immunity against tetanus is assessed and appropriate action taken. Trivial superficial cellulitis can be managed expectantly. The area of redness is ‘mapped out’ with an indelible pen so that its extent can be monitored. Spreading cellulitis is an indication for antibiotic therapy. Many infected wounds heal rapidly without further surgery, particularly if the original skin incision is placed in the line of least tissue tension. The problem is often to keep the wound open, rather than to achieve closure. If it appears that spontaneous wound closure will take a long time, secondary suture or skin grafting can be considered to speed healing, but only once it is clear that infection has been eradicated. The presence of clean healthy granulation tissue in the wound is usually a good indication that closure can be undertaken.

Skin grafts

These may be split-skin or full-thickness. Split-skin grafts are cut with a special guarded freehand knife or an electric dermatome. The donor site heals by re-epithelialization from epithelial appendages in the dermis within 2–3 weeks, depending on the thickness of the graft. To cover very large areas, the graft can be expanded by ‘meshing’. The thinner the graft, the more easily it will take on a bed of imperfect vascularity but the poorer the quality of skin will be and the more it will shrink. Split-skin grafts are used to cover wounds after acute trauma, granulating areas and burns, or when the defect is large. A full-thickness graft leaves a donor defect (which needs to be sutured or grafted) as large as the one to be filled and requires a well-vascularized bed to survive. However, such grafts are strong, do not shrink, and look better than a split-skin graft. They are rarely advisable after acute trauma but are commonly used in reconstructive surgery to close small defects where strength is needed (e.g. on the palm of the hand) or where a good functional and/or cosmetic result is important (e.g. on the lower eyelid). An area where there is skin to spare is chosen for the donor site (e.g. the groin for the former and the area behind the ear or upper eyelid for the latter).

Flaps

Whereas grafts require a vascular bed to survive, flaps bring their own blood supply to the new site. They can therefore be thicker and stronger than grafts and can be applied to avascular areas such as exposed bone, tendon or joints. They are used in acute trauma only if closure is not possible by direct suture or skin grafting, and are more usually reserved for the reconstruction of surgical defects and for secondary reconstruction after trauma. The simplest flaps use local skin and fat (local flaps), and are often a good alternative to grafting for small defects such as those left after the excision of facial tumours (Fig. 18.7). A flap may have to be brought from a distance (distant flap) and remain attached temporarily to its original blood supply until it has picked up a new one locally (Fig. 18.8). This usually takes 2–3 weeks, after which the pedicle can be divided. Advances in our knowledge of the blood supply to the skin and underlying muscles have led to the development of many large skin, muscle and composite flaps, which have revolutionized plastic and reconstructive surgery. One example is the use of the transverse rectus abdominis musculocutaneous (TRAM) flap for reconstruction of the breast. The ability to join small blood vessels under the operating microscope now allows the surgeon to close defects in a single stage, even when there is no local tissue available, by free tissue transfer (Fig. 18.9). Other tissues, such as bone, cartilage, nerve and tendon, can also be grafted to restore function and correct deformity after tissue damage or loss.

Fig. 18.7 Local skin flap used to repair a defect after the excision of a skin lesion.

A Before surgery. B After surgery.

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