Plastic and reconstructive surgery

18 Plastic and reconstructive surgery






Structure and functions of skin


Skin consists of epidermis and dermis. The epidermis is a layer of keratinized, stratified squamous epithelium (Fig. 18.2) that sends three appendages (hair follicles, sweat glands and sebaceous glands) into the underlying dermis. Because of their deep location, the appendages escape destruction in partial-thickness burns and are a source of new cells for reconstitution of the epidermis. The basal germinal layer of the epidermis generates keratin-producing cells (keratinocytes), which become increasingly keratinized and flattened as they migrate to the surface, where they are shed. The basal layer also contains pigment cells (melanocytes) that produce melanin, which is passed to the keratinocytes and protects the basal layer from ultraviolet light.



The dermis is composed of collagen, elastic fibres and fat. It supports blood vessels, lymphatics, nerves and the epidermal appendages. The junction between the epidermis and the dermis is undulating where dermal papillae push up towards the epidermis.


The three types of epidermal appendage extend into the dermis and, in some places, into the subcutaneous tissues. Hair follicles produce hair, the colour of which is determined by melanocytes within the follicle. The sebaceous glands secrete sebum into the hair follicles, which lubricates the skin and hair. The sweat glands are coiled tubular glands lying within the dermis and are of two types; eccrine sweat glands secrete salt and water on to the entire skin surface, while apocrine glands secrete a musty-smelling fluid in the axilla, eyelids, ears, nipple and areola, genital areas and the perianal region. Hidradenitis suppurativa affects the latter.


The nails are flat, horny structures composed of keratin. They arise from a matrix of germinal cells, which can be seen as a white crescent (lunula) at the nail base. If a nail is avulsed, a new nail grows from this matrix. If the matrix is destroyed, nail regeneration is impossible, and the layer of epidermal cells covering the nailbed thickens to form a keratinized protective layer.



Wounds


A wound may be defined as disruption of the normal continuity of bodily structures due to trauma, which may be penetrating or non-penetrating. In both cases, inspection of the body surface may give little indication of the extent of underlying damage.




Principles of wound healing


The essential features of healing are common to wounds of almost all soft tissues, and result in the formation of a scar. Soft tissue healing can be subdivided into three phases (Table 18.1) according to the development of tensile strength (Fig. 18.3).


Table 18.1 Phases of wound healing











Lag phase (2–3 days)

Incremental or proliferative phase (approximately 3 weeks)
Plateau or maturation phase (approximately 6 months)









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.






Factors influencing wound healing


Many of the factors influencing healing are interrelated: for example, the site of the wound, its blood supply, and the level of tissue oxygenation. Although some adverse factors, such as advanced age, cannot be influenced, others, such as surgical technique, nutritional status and the presence of intercurrent disease, can be modified or eliminated.




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.









Wound infection



Classification


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



Clean procedures are those in which wound contamination is not expected and should not occur. An incision for a clean elective procedure should not become infected. In clean operations, the wound infection rate should be 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 nevertheless present, perhaps because of the opening of a viscus, such as the colon. Infection rates in excess of 5% may suggest a breakdown in ward and operating theatre routine.


Contaminated or ‘dirty’ wounds are those in which gross contamination is inevitable and the risk of wound infection is high; an example is emergency surgery for perforated diverticular disease, or drainage of a subphrenic abscess.


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






Involvement of other structures


All wounds must be inspected carefully in good light to assess the extent of devitalization and injury to other structures. However, it is important to appreciate that a small, apparently innocent wound may conceal extensive damage to deeper structures. Body cavities may have been penetrated, or tendons, nerves and blood vessels divided. Damage to muscles, tendons or nerves is assessed by checking relevant motor and sensory function. If the injury



involves a limb, the distal circulation must be checked. Where appropriate, X-rays will help to establish whether peritoneal, pericardial or pleural cavities have been entered, and whether there is underlying bony injury.


Provided there is no deep damage, small, relatively uncontaminated wounds can be treated under local anaesthesia in the A&E department. The wound margins are cleaned with a mild antiseptic such as cetrimide and the wound is irrigated with sterile saline. Any devitalized tissue is removed, deep tissues are sutured with absorbable material and the skin margins are closed.


More extensive or severely contaminated wounds usually require inpatient treatment, with exploration and debridement under general anaesthesia. The wound and its margins are cleansed and all obvious foreign material picked out. Devitalized tissue is trimmed back until bleeding occurs. In areas of poor vascularity such as the leg, or if there is severe contamination, crushing or a fracture, the wound margins are formally excised (Fig. 18.6). Bleeding from the wound margin is not a certain indication of its ultimate survival, as impaired venous drainage can lead to progressive necrosis, particularly after a crushing or degloving injury. If there is any doubt, the wound should not be sutured and a ‘second-look’ dressing change should be undertaken under anaesthesia after 48 hours.



Primary closure should be avoided if there is significant delay in treating a grossly contaminated wound: that is, more than 6 hours without antibiotic cover. If primary closure is attempted, wound infection and breakdown are likely and there is a risk of anaerobic infection. It is also too late for formal excision but foreign bodies and dead tissue should be removed in the usual way. The wound is dressed and antibiotics are started. The dressing is changed daily, and if the wound is clean, delayed primary suture may be carried out after 48 hours. If closure is delayed, any granulation tissue is usually excised and secondary suture performed. If this is not possible, split-skin grafts (see below) can be applied to the granulations.


Provided that surgical treatment is carried out early, prophylactic antibiotics are only required for deeply penetrating wounds, especially those from dog and human bites or those caused by nails, where adequate debridement may be impossible. However, the early use of antibiotics in situations where a delay in surgical treatment is anticipated may allow primary suture of wounds after 8–12 hours, an interval that is normally considered safe.




Wounds with skin loss


If skin has been lost as a direct result of trauma, or following the excision of a tumour or necrotic tissue, direct suture may not be possible. A small skin defect at a functionally or aesthetically unimportant site may be allowed to heal by secondary intention. However, it is often better to speed healing by importing skin to close the wound by means of a skin graft, which requires a vascular bed as it has no blood supply of its own, or a flap.




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.


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Mar 20, 2017 | Posted by in GENERAL SURGERY | Comments Off on Plastic and reconstructive surgery

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