Brian S. Jewett

Skin Anatomy and Physiology

The epidermis, the most superficial layer of skin, consists of keratinizing stratified squamous epithelium. The predominant cell type is the keratinocyte, making up 80% of the cells. Layers of the epidermis include the basal cell, prickle cell, granular cell, and keratin layers; the overall thickness of human skin varies from 0.075 to 0.15 mm. The epidermis is thin at birth, becomes thicker during early adulthood, and thins during the fifth to sixth decades of life.

The epidermis is attached to the dermis by a basement membrane zone that extends from the epidermis to pilosebaceous units and sweat ducts located in the dermis. Each pilosebaceous unit contains sebaceous glands, a hair shaft and follicle with associated arrector pili muscle, and a sensory end organ. Epithelialization of partial-thickness skin wounds occurs from wound edges and the basement membrane zone around the hair follicles, sebaceous glands, and sweat ducts.¹

The dermis consists of a fibrous connective tissue matrix made up of collagen, elastic tissue, and ground substance. Dispersed throughout the dermis are epidermal appendages, blood vessels, nerves, and cells. The most common cell in the dermis is the fibroblast. Fibroblasts have a synthesis role in wound healing, producing collagen, elastin, and ground substance. Fibroblasts behave like contractile cells during wound maturation.

The dermis is divided into a thin papillary and a thicker reticular dermis. The overall thickness of the dermis is variable, depending on its location. Eyelid skin has the thinnest dermis, measuring less than 1 mm thick. Dermal thickness measures 1.5 mm on the temple, 2.5 mm on the scalp, and more than 4 mm on the back. The dermis is thin at birth, increases in thickness until the fourth or fifth decade, and then decreases with further aging. On average, men have a thicker dermis than women do.¹

Cutaneous blood flow is directed toward the more metabolically active epidermis through dermal papillae, hair papillae, and adnexal structures. Two vascular plexuses connected by communicating vessels are present in the reticular dermis. A deep plexus lies at the junction of dermis and fat; the superficial plexus gives rise to a rich capillary loop system in the superficial dermal papillae. This system provides nutrients to the epidermis through diffusion.²

Skin Grafts

On occasion, superficial facial defects are best addressed by repair with a skin or composite graft. Very young patients with tight facial skin presenting with large cutaneous defects are appropriate candidates for reconstruction with a full-thickness skin graft. Use of a skin graft is usually reserved for those cases that cannot reasonably be reconstructed with a local flap because of the size of the defect. The skin graft obviates the need for additional scars on the face or the use of a distant or microsurgical flap. Unfortunately, full-thickness skin grafts used in such cases frequently have a “patch” appearance, with discrepancies of color and texture between native and grafted skin (Fig. 15-1). Color and texture discrepancies between facial skin and skin grafts may also be a problem in elderly patients (Fig. 15-2). However, because of the tendency for elderly patients to have thin skin, grafts used to repair facial defects are more likely to display a better color and textural match with native facial skin than when similar grafts are used in younger patients (Fig. 15-3). Postoperative dermabrasion assists in minimizing color and texture discrepancies between skin grafts and facial skin.

Skin grafting involves removal of skin from one location and placement at a separate site. Skin grafts can be harvested in several different forms, including full thickness, split thickness, and composite. Regardless of the type of skin graft, graft viability depends on several factors: vascularity of the recipient site, microcirculation on the surface of the recipient site, vascularity of donor graft tissue, contact between graft and recipient site, and whether the patient suffers from certain systemic illnesses.

Contact between the skin graft and recipient site is essential. A bolster dressing is helpful to prevent fluid collections beneath the graft postoperatively (Fig. 15-4). Bolsters also prevent shearing forces from disrupting vascular connections between graft and wound bed. Systemic illnesses that may compromise graft survival include collagen vascular diseases, hematologic disorders, diabetes, nutritional deficiencies, and hypoxemia.³ Use of tobacco products is also detrimental to the survival of skin grafts.

Recipient site conditions that are not favorable to skin graft survival include irradiated tissue; scar; exposed bone, cartilage, or tendon; and bleeding wounds. Grafts placed over avascular defects smaller than 1 cm² may survive by nutritional support through the wound edges; however, grafting over larger avascular wounds is unlikely to succeed.³ Skin graft survival on bone is enhanced if a thin layer of bone is removed with a diamond fraise bur until punctuate bleeding is achieved. On the skull, holes can be made in the outer bone table to allow communication with the inner diploë. Large areas of exposed bone, cartilage, or tendon may require coverage with a muscle or fascial flap before grafting. Another technique that has proved successful in skin grafting auricular cartilage devoid of perichondrium is to create windows through the cartilage, exposing perichondrium and subcutaneous tissue on the opposing surface of the ear. The windows are made as large as possible through the cartilage in areas that can be resected without jeopardizing the structural integrity of the ear. The windows provide a port for vascular ingrowth to revascularize the graft (Fig. 15-5). Only very thin full-thickness skin grafts should be used for covering auricular cartilage so that the graft will not obscure the complex and delicate topography of the cartilage. Thin skin grafts are more likely to survive compared with thick full-thickness skin grafts, given the limited contact with a vascular source for nourishment.

For deeper wounds, skin grafting may be delayed until granulation tissue has filled the wound bed (2-3 weeks). Any epithelium on the surface of the granulation tissue is removed before grafting, and the tissue is crosshatched so that myofibrils are released. Granulating wounds normally contain bacteria. Bacterial counts greater than 10⁵ organisms per gram of tissue often lead to graft loss.⁴ When delayed grafting is planned, the patient is prescribed a 10-day course of an antistaphylococcal antibiotic to begin 3 days before skin grafting. When necessary, wound culture specimens are obtained to direct antibiotic selection.

Defect Preparation

Facial defects occasionally involve multiple facial aesthetic regions. In considering reconstructive options, it is helpful to mark the division between different regions so that defects involving multiple regions can be repaired with separate methods. Following this principle enables the placement of scars along boundary lines. This in turn helps preserve the natural contours of the face.

The aesthetic facial regions and their individual aesthetic units are based on variations in skin thickness and texture as well as on variations in contour created by the underlying facial framework. Optimal repair of a defect may require repositioning of skin and soft tissue within an involved aesthetic unit, thereby allowing eventual scars to lie within zones of transition between adjacent units. In addition, small defects may be enlarged to facilitate resurfacing of an entire aesthetic unit by a single repair method.

Establishing uniform wound depths and maintaining symmetry with contralateral facial regions are equally important. Before skin grafting, beveled tissue at the periphery of defects created by micrographic surgery is freshened, but the bevel is maintained to provide a gradual contour transition between the skin graft and adjacent facial skin. Additional techniques helpful in optimizing repair include angulation of curvilinear defects because round defects are more likely to undergo concentric scar contraction and result in trap-door deformity. Modifying the periphery of the defect by creating more acute angles often reduces the risk of this deformity.

Full-Thickness Skin Grafts

Full-thickness skin grafts consist of epidermis and full-thickness dermis (Fig. 15-6). They resist contraction, have texture and pigmentation similar to normal skin, and require a well-vascularized, uncontaminated recipient site for survival. Full-thickness grafts survive initially by diffusion of nutrition from fluid at the recipient site, a process known as plasma imbibition. Vascular inosculation occurs during the first 24 to 48 hours. After 48 to 72 hours, capillaries in the recipient site begin to grow into the graft to provide new circulation. By 3 to 5 days, a new blood supply has been established. Initially, full-thickness skin grafts appear blanched; however, during 3 to 7 days, a pink color develops, signaling neovascularization. After 4 to 6 weeks, the pink color begins to fade, and the graft will often remain lighter than the surrounding skin, especially in dark-skinned individuals.

Compared with split-thickness skin grafts, full-thickness skin grafts have the advantage of better color and texture match, fewer contour irregularities, no need for special equipment to harvest the graft, and easier donor site wound care. The disadvantages include reduced survival rate for larger grafts and longer healing time.³

Full-thickness skin grafts are well suited for defects located in thin-skinned areas of the face (eyelids, nasal sidewall, columella) and for defects involving concavities (temple, medial canthus) (Figs. 15-7 and 15-8). Full-thickness skin grafts used to repair defects of the face in regions of thicker skin tend to heal with a contour depression and noticeable textural discrepancies between graft and adjacent skin. This is because the skin in these areas contains more sebaceous glands and has a thicker dermis than the graft. However, contour discrepancies between skin grafts and adjacent nasal skin frequently improve with time as scar tissue forms beneath the graft (Figs. 15-9 and 15-10). If a skin graft has resulted in a persistent contour depression, the appearance of the graft may be improved by placement of a dermal fat graft beneath the skin graft after it has healed (Fig. 15-11). Meyers et al⁵ described the use of dermal grafts at the time of skin graft placement to help prevent contour depression after repair of deeper defects. Their technique involves the placement of dermal tissue in linear strips within the wound bed, leaving adequate exposure of the wound bed to provide nourishment to an overlying skin graft.⁵ The author’s preference is to perform a delayed dermal fat graft 3 months postoperatively if a significant contour deformity exists.

The ideal cutaneous defect to repair with a full-thickness skin graft is superficial, with loss of skin but not underlying muscle. The vascularity of shallow wounds is greater than that for defects extending through the muscle to the underlying cartilage or bone. The ideal defect is separated from the free margin of critical structures, such as the eyelid, nostril, and vermilion.

There is a wide variation of skin thickness among individuals, and the overall thickness of the facial skin is an important preoperative consideration. For similar defects, a skin graft may provide a perfect match in terms of thickness for one person and a poor match for another. There are individuals who have thin skin covering the entire face. These individuals are often fair-skinned elderly women, and full-thickness skin grafts may be used in these patients for superficial cutaneous defects anywhere on the face without concern for color or textural discrepancies between graft and facial skin (Fig. 15-12). The only exception to this rule is in the area of the margins of the nostril, eyelid, and vermilion; scar contraction after skin grafting will likely distort the border of these structures.

A number of donor sites for skin grafts are available in most individuals, depending on the location and size of the facial defect. Donor sites include upper eyelid, forehead, melolabial fold, preauricular, postauricular, and supraclavicular areas (Fig. 15-13). In selecting a donor site, the thickness of the skin surrounding the recipient site is assessed and donor skin is selected accordingly. Regions of the face with thicker skin include the forehead, medial cheek, caudal nose, and chin. Skin defects in these areas can be repaired with grafts from contralateral facial donor sites and periauricular or supraclavicular areas (Fig. 15-14). Regions of the face with thinner skin, such as the eyelids and cephalic two-thirds of the nose, are best repaired with skin grafts obtained from the eyelid or periauricular area that are thinned appropriately. Skin grafts harvested from the postauricular area are often preferred in men because they are hairless. Men tend to have shorter hair than women do, causing the postauricular skin to more likely manifest solar aging, which provides an improved skin color match with the facial skin (Fig. 15-15). In contrast, preauricular skin is often the preferred source for skin grafts in women. Preauricular skin in women is hairless and has more solar aging compared with postauricular skin. The supraclavicular region is an excellent source for skin grafts, especially if a large graft is required (Fig. 15-16). Supraclavicular skin has moderate thickness, but the dermis of this donor skin can be thinned so that the thickness of the graft will match the depth of the recipient site.⁶

There are occasions when the author will use skin grafts to repair shallow skin defects of the face even when it is anticipated that the graft will result in a contour depression or noticeable mismatch of skin texture or color with adjacent native skin. These situations often arise in caring for elderly debilitated patients who have life-threatening illnesses. Another indication for use of a skin graft in place of a more desirable local flap is in patients who have skin malignant neoplasms with aggressive histologic growth patterns that predispose the patient to recurrent tumor. In these instances, skin grafts may be used as a temporary covering for a 2- or 3-year interval while the patient is at greatest risk for recurrence of the skin cancer.

Defects involving more than one facial region are often repaired with separate techniques. For example, defects located on the lateral nasal ala immediately adjacent to the nasofacial sulcus may be repaired by a number of options. If the defect extends into the cheek, the cheek component of the defect is usually repaired with a cheek advancement flap. The alar component may be repaired with an interpolated cheek or paramedian forehead flap if the defect is large. For smaller defects, especially in very young patients, full-thickness skin grafts and composite grafts are considered. Full-thickness grafts are best suited for superficial defects not extending to the nostril border. In the case of deep alar defects, skin grafts do not lend any structural support, and subsequent nasal valve collapse may lead to compromise of the nasal airway. One option for patients with small, laterally located deep alar defects is the transfer to the defect of subcutaneous cheek tissue in the form of a hinge flap (Fig. 15-17). The flap partially fills the defect and nourishes a cartilaginous alar framework graft placed deep to the hinge flap to lend structural support to the nostril. A full-thickness skin graft is placed as an external covering over the hinge flap, thereby completing a single-stage reconstruction (Fig. 15-18).⁷

When skin defects of the nasal sidewall that extend to the medial cheek are repaired with a skin graft, the cheek component of the defect is reconstructed with a cutaneous advancement flap developed from the remaining medial cheek skin. The flap is advanced to the level of the nasofacial sulcus and anchored in place with deep sutures that pass from the medial border of the flap to the periosteum of the nasal sidewall. A full-thickness skin graft is then used to resurface the sidewall. The cheek advancement flap enables the placement of scars in the aesthetic boundary between the cheek and nose. If the cheek defect is of considerable size, the standing cutaneous deformities that occur from advancement of the cheek flap may be excised and used as full-thickness skin grafts to cover the sidewall defect (see Fig. 15-17).

Defects of the upper and lower eyelid that involve skin and potentially muscle are often repaired with adjacent tissue; however, this may not be available in sufficient quantity, and reliance on local tissue only for repair could result in a significant secondary deformity. For superficial defects of the eyelids, skin grafts are a reasonable option. Donor sites for the graft include the opposing and contralateral eyelids, which provide skin with similar texture and thickness. When skin grafts are used for periocular reconstruction, it is important to determine whether the structural integrity of the eyelid will withstand contraction forces associated with healing. For example, in lower eyelid reconstruction, tightening of the lower eyelid by a lateral tarsal strip procedure may help prevent development of ectropion or eyelid retraction. In addition, the author routinely uses a temporary lower eyelid suspension suture (Frost suture) during the initial 2 weeks after lower eyelid skin grafting. By suspending the orbicularis muscle, adhesions within the muscle that could lead to lower eyelid retraction are avoided, and the likelihood of ectropion is minimized.

Split-Thickness Skin Grafts

Split-thickness skin grafts consist of epidermis and a variable portion of underlying dermis. They have more capillaries exposed on their undersurface compared with full-thickness grafts, permitting greater absorption of nutrients from the wound bed. In addition, split-thickness skin grafts consist of less tissue that requires revascularization. As a result, split-thickness grafts are often used for wounds in which revascularization is a concern. However, because of their likely poor color and texture match with normal skin and their tendency to contract, split-thickness skin grafts are selectively used in facial reconstruction. Some indications for split-thickness skin grafts are to cover defects too large to be repaired with a local flap (Fig. 15-20), to facilitate monitoring for potential cancer recurrence, and to provide temporary coverage of a wound bed before definitive reconstruction. Most split-thickness grafts are between 0.012 and 0.030 inch in thickness; thicker grafts have a relatively better color and texture match with facial skin.³

Composite Chondrocutaneous Grafts

Composite grafts contain two or more tissue layers and often are unsuccessful secondary to high metabolic demands.¹⁰ They obtain their nourishment through plasma imbibition during the first 24 hours after transfer. This is followed by vascular inosculation. Ingrowth of capillaries from the edges of the graft begins by the third day.^11,12

Composite grafts were first described by Konig,¹³ who used composite auricular grafts to repair alar defects, noting a 53% graft survival. Composite grafts have been used to repair columellar defects^14,15 and deficiencies in nasal lining.¹⁶ During the first half of the 20th century, Limberg¹⁷ advocated the cavum and cymba of the concha as the preferred donor site of composite grafts used to repair the nose, and Gillies¹⁸ described the transfer of composite grafts to the undersurface of forehead flaps for nasal reconstruction. Symonds and Crikelair¹⁹ also used composite auricular grafts for nasal reconstruction, reporting an 89% graft survival rate.

Composite grafts are commonly used to repair small full-thickness nasal defects. The auricle is an excellent donor source for composite grafts used for nasal reconstruction because it provides a contoured graft of skin and cartilage (Fig. 15-23). Certain segments of the auricle can loosely replicate the delicate topography of the columella, facet, and nostril margin, where composite grafts are commonly employed. The skin is tightly attached to the underlying cartilage at the columella and to the fibrofatty tissue of the alae and facets. Likewise, the skin covering the lateral aspect of the auricle is firmly attached to the underlying cartilage. Common auricular donor sites are helical crus, helical rim, antihelix, tragus, antitragus, and fossa triangularis. The helical crus provides a good contour match for small nostril margin defects and provides the option of incorporating in the graft a segment of preauricular skin. Incorporation of preauricular skin with the composite graft is useful for resurfacing of larger nasal defects requiring considerable skin but minimal framework replacement.⁶

The traditional recommendation is to limit the size of composite grafts to 1 cm or less.²⁰ Considerably larger grafts may be successful if they are placed in a vascular recipient site and the graft is designed so that no portion is more than 1 cm from a wound edge.^21–24 Skouge advocated a tongue-and-groove technique when composite grafts are used. This technique involves insetting the border of the graft between two layers of tissue at the recipient site.⁴ This method of graft attachment has the effect of increasing surface contact between graft and recipient site by 50%.²⁰ If a defect is allowed to heal by secondary intention and then reconstructed with a composite graft, there is a greater success rate. In such instances, a hinged flap of scar and epithelium formed during secondary healing can be dissected to increase the surface area for attachment of a composite graft (Fig. 15-24).²⁵

The ideal nasal defect for a composite auricular graft is a small (1 cm or less) full-thickness defect of the facet, columella, or nostril margin. The nasal skin in these areas is extremely thin, lacking subcutaneous fat, and is tightly attached to the alar cartilage in the case of the columella and fibrous connective tissue in the case of the facets and alae. Skin flaps used to repair the facet or columella convey skin with subcutaneous fat and are thicker than the native nasal skin. In contrast, composite auricular grafts obtained from the helical crus provide a graft with thin skin attached to a delicate segment of cartilage. The cartilage provides structural support, and the skin closely resembles the adjacent nasal skin of the columella and facet (Fig. 15-25).

Perhaps more commonly, composite grafts are used to repair small defects of the nostril margin (Fig. 15-26). Deep wounds in this location may lead to notching of the nostril margin. Composite grafts may be used to maintain structural integrity and to provide a smooth continuous border to the nostril.⁷ Weisberg and Becker²⁶ described the use of auricular composite grafts with stabilizing struts for repair of such defects. The stabilizing struts are extensions of cartilage that are placed beneath the adjacent nasal skin in a tongue-and-groove fashion similar to Skouge’s original description (see Fig. 15-25).

The use of perioperative corticosteroids is beneficial in enhancing survival of composite grafts in animals. Rabbits treated with preoperative and postoperative methylprednisolone demonstrated improved graft survival compared with animals receiving no steroids or postoperative doses only. Attempts to salvage compromised grafts with delayed administration of steroids were not successful.27,28 Cooling of composite grafts has also been demonstrated to improve survival. Cooling reduces biologic requirements and improves graft survival in irradiated, atrophic, or scarred recipient sites. Conley demonstrated that constant application of ice and ice compresses for 14 days effected a fall in skin temperature from 38°F to 17°F. Composite grafts ranged in size from 1 × 1-cm to 2 × 2-cm. Of 12 composite grafts transferred to the nose and treated with ice compresses, 10 survived completely. Five of the grafts had been placed in recipient sites with scarring or postirradiation fibrosis.²⁹

Other Composite Grafts

Other types of composite grafts have been described for nasal reconstruction. Composite grafts consisting of skin and subcutaneous fat from the earlobe or full-thickness segments of the contralateral alar base may be used to repair defects of the alar base or nostril margin.¹³ Stucker and Shaw³⁰ described the use of perichondrocutaneous grafts that consist of epidermis, dermis, scant subcutaneous tissue, and a perichondrial layer. The grafts are harvested from the cavum concha, and an island pedicled skin flap from the postauricular sulcus is used to repair the donor site. These authors reported excellent aesthetic results, with no contraction of the graft.³¹

Composite grafts may also be used in eyelid (see discussion in Chapter 17) and eyebrow reconstruction. Tarsoconjunctival grafts are sometimes used for reconstruction of the posterior lamellae of the eyelid. Furthermore, strip grafting, involving the transfer of skin, hair follicles, and fat from the scalp, has been used for eyebrow reconstruction (Fig. 15-29). Survival may be impaired in eyebrow defects that are severely scarred. Although the results are acceptable, strip grafting has been largely replaced by microfollicular hair transfer.³ The multidirectional orientation of eyebrow hair should be considered during eyebrow reconstruction (Figs. 15-30 and 15-31).

References