• Choosing the right suture material
• How to suture
• Local anaesthetics

In the fourth part of our series, Ben Taylor and Ardeshir Bayat explain the first few steps on the reconstructive ladder -- primary closure and skin grafts

Closing wounds and defects is a basic surgical skill. Plastic surgeons manage large, infected, or complex defects with a range of techniques; the idea of the "reconstructive ladder" is useful (fig 1). On the lower rungs are simple techniques; if these are not adequate, you can climb the ladder. As with real ladders, however, climbing too high too soon may be dangerous for your patient. Start at the bottom and consider each step carefully as you move up, until you have sufficient experience to know which rungs to jump.

Fig 1. The reconstructive ladder for plastic surgery

Ground floor: do nothing

The simplest way to treat a wound is to leave it to heal by secondary intention. This is not as uncaring as it sounds--our bodies evolved over millions of years to do this. Secondary intention allows the wound to drain and heal from the base up and is particularly appropriate for:

• insignificant and small wounds--for example, a small paper cut
• infected wounds--closing an infected wound will trap the infection, until it breaks down the wound
• when blood supply is compromised--closing the wound would further imperil blood supply

Even though you do not take measures to close the wound, you can do a lot with judicious application of dressings. The main disadvantage to this simple method is the look of the healed wound--you rely on scar contraction to close the wound. The wound edges may not have aligned well, and the end result may be a large scar that distorts the normal contours of the body.

First step: primary closure

The next step up from secondary closure is primary closure. You can use sutures, staples, wound glue, and adhesive strips to close the edges of the wound directly and splint the wound in the position that will give the best cosmetic result.¹ Primary closure is perfect for small neat wounds which are not infected, have a good blood supply, and are not under undue tension. You must remember that a wound heals despite sutures, rather than because of them, and that inappropriately placing sutures will rapidly lead to them breaking down.

If the wound is not suitable for direct primary closure, an alternative is delayed primary closure. This simply allows a period of secondary intention healing to progress to cause the wound to contract enough to let you close it directly. Vacuum assisted dressings may speed up healing (evidence is limited but increasing).² Delayed primary closure is often used when it is not clear if the wound has been adequately prepared--for example, a non-contaminated wound with viable skin flaps or a wound with edges that you cannot quite get together.

Moving up the ladder: skin grafts

What if, when assessing a wound, you find a large defect which is not amenable to primary closure, for which secondary closure is not suitable? If this defect is purely skin loss, with a healthy bed of tissue underneath--for example, an uncomplicated burn--then simply finding some way to replace the lost skin may be the best bet. A skin graft is an autologous (material is taken from one part of a patient to another anatomical site on the same patient) transplantation of skin, which in the process of transfer, is completely separated from its blood supply.

A skin graft used to help heal a leg ulcer

Why do we need a skin graft?

The skin is divided into layers--the epidermis, dermis, and hypodermis (subcutaneous fat). The dermis is the structural matrix, of mainly collagen, containing blood vessels, nerve endings; the dermis provides structure and support to the skin. Above this, a relatively thin layer of keratin filled cells--the epidermis--provides protection against chemical, biological, and thermal insults; dehydration; and radiation.³ The epidermis grows slowly from the edges to cover smaller wounds. In addition, structures, such as hair follicles and sweat glands extend from the surface of the skin deep into the dermis. These structures bring with them a small layer of epidermal cells, from which a functioning epidermis can regenerate in partial thickness loss. If, however, the full thickness of the skin is lost, the defect will have no protective or barrier functions and will not be able to regenerate because all epidermal components will have been removed. Therefore, to restore the function of the skin as quickly as possible, a layer of skin can be taken from a normal part of the body (donor site), and grafted on to the defect (recipient site). Skin grafts provide a source of cells to grow over the damaged area and act as biological dressings to protect the wound.

The process of "take"

When you graft a sheet of living cells without a blood supply, the cells must "take" nutrients from somewhere. A basic understanding of this process is essential when caring for a patient with a skin graft. For the first 48 hours, cells in the graft imbibe nutrients from serum at the recipient site.⁴ During this time, fibrin bonds the graft to the recipient surface. After 48 hours, the capillaries in the recipient site and those in the graft align (inosculation).⁵ Once the capillaries are aligned, blood flows through them to reperfuse the graft.

Where is a skin graft suitable?

The process of take is a precarious one. For the graft to take, it must remain in close contact with the recipient site. Any shearing forces will disrupt the fragile capillaries on which the graft depends for its survival causing the graft to fail. Obviously, there have to be some capillaries to grow into the graft, so the recipient site must therefore have a good blood supply. The recipient site must be surgically clean, although most commensal flora are not normally a problem.⁶ However, even small amounts of group A streptococci or Pseudomonas aeruginosa can cause a graft to fail.

For a skin graft to take, the recipient site must be vascular and free of infection. Avascular tissues such as cartilage and exposed cortical bone will not take a graft. Infection will disrupt a graft; therefore removing dead tissue and ensuring that haemostasis is adequate are essential. Creams such as silver sulphadiazine can be used as an antiseptic to prepare the wound to reduce the risk of infection. Early excision of burns removes dead tissue that could act as a source of infection.⁷ Any barrier between the graft and the bed will cause the graft to fail. One common barrier is blood, from the recipient site (haematoma). Any particularly troublesome bleeding should be stopped with diathermy. Overuse of suction to clear the bed makes the problem worse by removing clots that have already formed. When you place the graft, make sure you get it the right way up. The shiny side of a graft is the bottom of the dermis and goes onto the wound. Pressure dressings are well suited to keeping the graft close to the wound and minimise movement. Resist the temptation to peek at the graft on every ward round, as you risk disrupting the graft when you fiddle with the dressings. Look at the graft five to seven days after the procedure, to minimise the risk of disrupting the graft in the precarious stage of take.⁸

Thickness of grafts

Skin grafts of a range of thicknesses can be taken (see table). Grafts may be full thickness or split thickness. A full thickness graft is a graft of the full thickness of the skin, including the whole dermis, from the donor site. Split thickness grafts are the epidermis and only part of the dermis. Take care when harvesting a graft from children, elderly people, or patients taking corticosteroids; their skin will be thinner than that of a healthy adult.⁹

Meshing

To increase the size of a split thickness skin graft, a meshing machine cuts little holes in the graft to create a net-like pattern. This also allows blood and fluid to escape, preventing the formation of a dreaded haematoma, and allows the graft to conform to the wound better. Unfortunately, meshing gives the scar an unsightly appearance when the wound has healed.

Meshing machines can be set to cut holes in the graft to give different ratios of expansion. The more a graft is expanded, the more surface area it will cover. The wound will heal more slowly in the spaces created by the meshing machine⁹; consider each space between the ribbons of skin as bare surface of the wound. See web extra.

Meshing is used to increase the size of a split thickness skin graft

Long term results

Although good results can be obtained with full thickness grafts on the face, skin grafts may give a poor cosmetic result. Initially, the graft will have no feeling but may recover some sensation over time if nerve fibres grow into it. The graft will not sweat because it has no sweat glands.

Further serious complications arise due to the healing process. Grafts, especially meshed grafts, contain a lot of scar tissue. Scar tissue contracts, which can be a problem around joints. Further complications can result from pathological scarring leading to hypertrophic or keloid scars.¹⁰ Physiotherapy prevents troublesome scars.

Storage of skin grafts

Skin grafts can be stored for up to four weeks at 4ºC,¹¹ which is useful if you have taken too much skin from the donor site, and you may wish to add more at a later date. Storage also allows delayed primary grafting and possibly fewer general anaesthetics.

If the patient does not have enough skin of their own--for example, victims of severe burns--not for profit skin banks can supply skin from cadavers. This skin is either frozen or preserved with glycerol, similarly to some replacement heart valves. However, because of the foreign nature of the skin, and the preservation methods used, this is not as permanent as a skin graft. It is best suited to use as a biological dressing,¹² to aid future grafting. Transplants of tissue carry the risk of blood borne infections such as HIV and hepatitis C.

Artificial skin

Within the past decade, a range of artificial skins has become available.¹³ These layered dressings attempt to recreate the normal architecture of the skin with prosthetic materials, such as silicone, seeded with biological materials. Some of the simpler artificial skins contain only collagen fibres, but newer ones contain fibroblasts derived from neonatal foreskin. Recent technology in engineering tissue gives the hope of using cultured autologous cells to replace skin--true artificial skin replacement. For the time being, however, artificial skin is merely a temporary dressing, which enhances the ability of the site to take a skin graft in the future. One such prosthesis is widely used in burnt patients to cover skin and promote dermal regeneration. It consists of a deep layer of collagen and glycosaminoglycan covered with a sheet of silicone. The collagen allows the dermis to regenerate so that thinner skin can be used, which has implications for regeneration of the donor site.¹⁴ Once ready, the silicone layer is removed and a thin skin graft applied.

What next?

If everything up to this point is unsuitable for closing a wound, more advanced techniques may be necessary. These techniques--some of the most exciting aspects of plastic surgery--will be discussed in next month's article.

Ben Taylor third year medical student
Email: bentaylor@doctors.org.uk

Ardeshir Bayat honorary lecturer and specialist registrar in plastic and reconstructive surgery, University of Manchester
Email: ardeshir.bayat@man.ac.uk

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9. Vandeput JJ, Tanner JC, Boswick J. Implementation of parameters in the expansion ratio of skin grafts. Plast Reconstr Surg 1997;100:653-6.
10. Bayat A, McGrouther DA, Ferguson MWJ. Skin scarring. BMJ 2003:326;88-92.
11. DeBono R, Rao GS, Berry RB. The survival of human skin stored by refrigeration at 4ºC in McCoy's 5A medium: does oxygenation of the medium improve storage time? Plast Reconstr Surg 1998;102:78-83.
12. Blome-Eberwein S, Jester A, Kuentscher M, Raff T, Germann G, Pelzer M. Clinical practice of glycerol preserved allograft skin coverage. Burns 2002;28(suppl):S10-12.
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Web extra - Skin grafts

Full thickness grafts differ from split thickness grafts in many ways. To harvest a full thickness graft, a scalpel is used to excise an ellipse of skin from a few key sites (see table 1), which is then prepared. The advantages of a full thickness graft include a better colour match and cosmetic outcome and less contraction as they heal. The disadvantages are that grafts need a good blood supply to take, as they contain the full thickness of the dermis. Therefore, they are usually only used on the face. There are a limited number of suitable donor sites, and each only gives a small area of graft. Harvesting a full thickness graft leaves a wound, which must then be closed. You cannot return to harvest more graft from the same site.

Split thickness grafts are more widely used. As only part of the dermis is taken, the donor site can regenerate. These grafts are harvested with either an electric dermatome or a special knife (Watson-Humby), and there are many more sites from where a graft can be taken. Huge amounts of graft can therefore be harvested to cover extensive burns. However, the cosmetic outcome is usually poor, and grafts will contract, which may limit motion around joints. The graft and donor sites often discolour.