Plastic surgery, including common skin and subcutaneous lesions

Inflammatory phase (days 1–6)

The initial phase begins with immediate vasoconstriction and coagulation, followed by vasodilation and increased vascular permeability that is mediated by histamine, nitric oxide (NO) and serotonin produced by platelets and endothelial cells. Neutrophils (1–2 days), macrophages (2–4 days) and lymphocytes (5–7 days) coordinate the inflammatory and growth factor response.

Proliferative phase (days 3–21)

Fibroblasts, attracted to the wound by a process known as chemotaxis, arrive by day 3 and predominate by day 7. They produce the collagen necessary for scar formation and remodelling. Angiogenesis, the ingrowth of new blood vessels under the influence of VEGF and NO, occurs simultaneously, and wound tensile strength increases steadily ( Fig. 19.4 ).

Maturation or remodelling phase (weeks 3–52+)

During weeks 3 to 5, the rate of collagen breakdown approaches and then temporarily surpasses its synthesis. Subsequently, there is no net increase in collagen within the wound, although it becomes more organised and better cross-linked. The type III collagen that predominates initially is gradually replaced by type I collagen, eventually restoring the normal ratio of 4:1, although skin and fascia usually recover only 80% of their original tensile strength.

Clinically, wound healing is considered to be complete once the surface of the wound has been reepithelialised, although remodeling continues for 2 years or more. Epidermal cells from the wound edges and from within the skin appendages are mobilised to migrate across the wound surface, multiplying as they do so, until contact is made with the opposing wound edges. At this point, contact inhibition is reestablished, and the cells differentiate once more to form the normal epidermal layers. Concurrently, myofibroblasts scattered throughout the wound lead to wound contraction, especially in the absence of viable dermis.

Blood supply

Any local or systemic condition that compromises the ability of blood to deliver oxygen and nutrients whilst removing waste products from the wound will adversely affect wound healing. This includes peripheral vascular disease, anaemia, cardiopulmonary disease, smoking and microvascular disease associated with diabetes, Raynaud disease and scleroderma. A poor surgical technique that damages or applies excessive tension to the wound edges can also render tissue ischaemic. Such wounds are more prone to infection and frequently break down because arterial oxygen tension (Pa o ₂ ) is a key determinant of the rate of collagen synthesis. Similarly, wound healing in previously irradiated areas is often impaired due in part to compromise of the circulation.

Infection

The risk of wound infection is a reflection of patient age, the mechanism of wound formation, its location and environmental exposure, the presence of intercurrent infection, steroid administration or other immunosuppression states, smoking, diabetes mellitus, severe malnutrition and cardiovascular or respiratory disease. Microbial contamination can be minimised by careful skin preparation, aseptic technique and thorough wound debridement of devitalised tissue and foreign material. Poor hand hygiene before and after patient contact is perhaps the single greatest source of infection spread. The immune system provides natural defences against microbial invasion. Common infecting organisms include skin commensals as well as opportunistic organisms such as staphylococci, streptococci, coliforms and anaerobes. Pseudomonal infections are common in burns and chronic wounds.

When wound contamination is anticipated, or the consequences of infection would be severe, prophylactic antibacterial treatment may be used topically or systemically. In acute traumatic wounds, tetanus prophylaxis is considered routinely, but antibiotics are not normally necessary if prompt treatment is undertaken.

Nutritional status

Protein, glucose and fatty acids are essential to wound healing, and in deficiency states, wound dehiscence and infection are common. Highly exudative wounds can contribute to total protein loss by up to 100 g each day. Healing problems should be anticipated if recent weight loss exceeds 20%.

Vitamin A is required for epithelial formation, cellular differentiation and normal functioning of the immune system, and supplements have been shown to mitigate the negative effects of steroids on wound healing. Vitamin C is essential for proline hydroxylation in collagen synthesis, and deficiency leads to reduced collagen production and tensile strength, immature fibroblast formation and capillary haemorrhage, all features of scurvy. Zinc is a cofactor for several important enzymes involved in healing. Other elements, including copper, iron and selenium, are also likely to be essential for promoting normal wound healing. Although supplements of trace elements and vitamins are effective in patients with known or suspected deficiencies, they do not appear to improve healing in normal subjects.

Intercurrent disease

Healing may be affected by concurrent disease or its treatment. For example, cancer may be associated with severe malnutrition and marked impairment of healing. Diabetes mellitus impairs healing by promoting infection and by causing peripheral vascular insufficiency and neuropathy. Haemorrhagic diatheses increase the risk of haematoma formation and wound infection. Respiratory disease may lower arterial oxygen tension, and coughing can contribute to abdominal wound dehiscence. Corticosteroids, immunosuppressive therapy, chemotherapy and radiotherapy contribute to poor wound healing through various mechanisms, including impaired cellular function and inflammatory response, impaired collagen synthesis and decreased resistance to infection.

Surgical technique

Tension-free primary wound closure and meticulous technique promote effective wound healing. Dead space should be avoided because the potential accumulation of blood and exudate encourages infection and increases tension on the wound. Drain placement can be helpful in the management of dead space, but drains should be removed as soon as possible and typically when the output falls below 40 mL/24 hours. Appropriate dressings are essential to protect the wound from infection, trauma and desiccation and to remove exudate whilst providing a favourable warm and moist environment.

Classification

• All surgical procedures can be classified as ‘clean’, ‘clean–contaminated’ or ‘contaminated’, according to the likelihood of intraoperative contamination and subsequent wound infection. Clean procedures are those in which wound contamination is not expected and the wound infection rate is less than 1%.

• Clean–contaminated procedures are those in which no frank focus of infection is encountered but where a significant risk of infection is present. Bowel surgery is a classic example. Infection rates of up to 5% may occur.

• Contaminated procedures are those in which gross contamination is already present or inevitable and the risk of wound infection is high. Examples include bowel perforations, trauma and drainage of an abscess.

Antibiotic prophylaxis may be considered for the first two, whereas contaminated wounds are very likely to require therapeutic antibiotics (for further details on perioperative antibiotic prophylaxis, see Chapter 4 ) .

Clinical features

Wound infection typically becomes evident 3 to 4 days after surgery, although it can be delayed if prophylactic antibiotics have been used. Earlier infections suggest significant contamination of the wound at the time of surgery or initial injury.

The clinical signs of infection include bright erythema radiating from the wound associated with swelling, discomfort or pain and discharge that is often malodorous. On palpation, there may be fluctuance indicative of an abscess, an infected haematoma or a seroma, whilst crepitus may be felt in the presence of gas-forming organisms. In deep-seated infection, there may be no signs on the skin surface, although the patient may have wound tenderness, pyrexia and other signs of sepsis. Toxaemia, bacteraemia and septicaemia can complicate any wound infection, especially where there is a collection of pus.

Prevention

Careful preoperative planning and preparation; meticulous aseptic technique, tissue handling and debridement; and the prophylactic use of antibiotics in high-risk patients all help reduce the risk of wound infection. Severely contaminated wounds may be left open for subsequent inspection and closed days later; most blast and gunshot wounds are treated in this way.

Management

In the event of infection, a wound swab or specimen of pus is sent routinely for bacteriologic culture and sensitivity determination. In urgent cases, Gram staining may be useful to indicate the class of bacteria involved. The area of erythema is ‘mapped out’ with an indelible marker so that progression can be monitored. Whilst minor superficial cellulitis can be managed expectantly, spreading cellulitis is an indication for intravenous antibiotic therapy, with drainage of an abscess or debridement of necrotic tissue as required. Antibiotic therapy is usually initiated on an empirical basis and refined later, depending on culture and antibiotic sensitivities .

Skin grafts

Skin grafts may be split- or full-thickness grafts. The former includes the epidermis and a thin layer of dermis and is harvested freehand using a specialised guarded blade (Watson knife) or by means of a powered dermatome. Split-thickness grafts can be harvested from any region of the body, although the thighs are commonly used for ease of access and their acceptable donor site morbidity. The donor site heals by secondary intent with rapid reepithelialisation from epithelial appendages within the remaining dermis. After just 2 to 3 weeks, the donor site can be reharvested once more if required. When it becomes necessary to cover very large wounds with a limited availability of donor sites (in major burns, for example), the graft can be ‘meshed’, permitting expansion of 1.5 to 6 times its original size.

Full-thickness skin grafts include the epidermis and all of the dermis, leaving a donor defect that must be closed directly or grafted. The graft size and donor sites are therefore limited; the neck, inner arm and groin are commonly used. The advantages of full-thickness grafts are that they exhibit less secondary contraction and generally produce a more aesthetic and robust scar; hence, they are commonly used in reconstructive surgery of small defects of the face and hands.

All grafts require close contact with a well-vascularised wound for nourishment and survival. They will not ‘take’ on bone, cartilage or tendon denuded of periosteum, perichondrium or paratenon. In such cases, fresh tissue with an intrinsic blood supply must be brought into the wound.

Flaps

Flaps, by definition, have an intrinsic vasculature and can be categorised by their components (skin, fascia, fat, muscle, bone or viscera such as bowel or omentum), their circulatory supply or ‘pedicle’ (random or named vessels, perforator vessels) and their congruity (local, distant or free). Thanks to the large variety of flap designs, they can be used to fill defects of any size, as well as to replace missing bone, muscle, tendon and nerve as required. The simplest flaps employ local skin, fat and fascia in various configurations (designs and methods of transfer) and are good alternatives to grafting for smaller defects, such as those resulting from the excision of facial tumours ( Fig. 19.6 ). Where no local option is suitable, a ‘distant’ flap may be brought to a wound whilst remaining attached temporarily to its original blood supply ( Fig. 19.7 ). After 2 to 3 weeks, the flap will have picked up a local blood supply, and the original pedicle can be safely divided.

When local or distant flaps are not available or appropriate, the pedicle of almost any flap can be divided and anastomosed to a donor artery and vein adjacent to the wound ( Fig. 19.8 ). These so-called ‘free’ flaps have almost completely replaced the need for the complex staged reconstructions that were commonly used before the introduction of microsurgical techniques in the developed world ( Fig. 19.9 ).

Major advances in our knowledge of the blood supply to the skin and underlying tissues have led to an explosion of new flap designs and compositions, which have revolutionised plastic and reconstructive surgery. One example is the use of the deep inferior epigastric artery perforator (DIEP) flap for reconstruction of the breast following mastectomy. Another is the masseter muscle transfer used to restore the ability to smile for patients with facial paralysis. The ability to join small blood vessels and nerves under the operating microscope allows the surgeon to close defects and restore both form and function in a single operation (see also Chapter 26 ).

Burn size

The approximate extent of any burn can be quickly calculated using a combination of three methods. The Wallace ‘rule of nines’ divides the body into areas that each represent approximately 9% of the total body surface area (TBSA) of an adult ( Fig. 19.10 ). However, this technique is less useful in children because of the relatively large head size (about 20% of body surface at birth) and small limbs (legs are about 13%). Burn injuries rarely conform to such neat patterns. Another commonly employed technique is based on the assumption that the surface area of the patient’s palm and closed fingers together constitute about 1% of their TBSA. Perhaps the most accurate and widely employed method is the Lund and Browder charts that provide a physical documentation of burn size and compensate for age ( Fig. 19.11 ). The charts also act as a visual medical record that can be helpful once the wounds are covered with dressings. Simple erythema usually subsides in a few hours and should not be included in calculations of overall burn size. Hypovolaemic shock is more likely with 15% (10% in children) surface burns, prompting the need for resuscitation fluids.

Burn depth

The accurate assessment of burn depth is critical because it indicates the likelihood of spontaneous healing and therefore the need for grafting. Superficial burns, like sunburn, are typically more painful, may present with blistering and blanch on pressure, whereas the deeper burns may be dry, waxy and painless, with no evidence of dermal circulation. Burn depth is classically subdivided into three groups, superficial, partial and full thickness. In North America and elsewhere, these are described as first, second and third degree, respectively. In practice, many burns are of mixed depth ( Fig. 19.12 ).