Complex Layered Facial Closures

Fundamental objectives of wound closure

Successful design of wound closure begins with an understanding of cosmetic subunits, tissue biomechanics, and anatomic layers of the skin and subcutaneous tissues. Structurally, the integument is best thought of as a multilayered unit of epidermis, fibrous connective tissue, subcutaneous adipose tissue, and muscle that provides structure and texture to the skin. Regional variations in the relative composition of these layers provide the characteristic textural qualities of various anatomic sites. These regional variations in skin quality and texture and their resultant qualitative effect upon the aesthetic appearance of the skin are most notable in the head and neck region. Careful attention to these regional variations is paramount for planning a reconstruction that best recreates the natural appearance. When primary closure is not an option, careful selection of local skin flaps and skin grafts that match both tissue color and texture of the recipient site will provide the best cosmetic outcome.

A second fundamental principle that should be obeyed when planning closures on the head and neck is to respect the natural lines of demarcation. Aesthetically, the face is composed of multiple cosmetic subunits (see 1.4, 1.5, 1.6 ). Natural skin folds, variations in tissue thickness and composition, and the underlying bony structure collectively create the natural lines of demarcation along these subunits. In most cases, these subunits have a corresponding symmetrical unit on the contralateral face. These natural undulations and demarcations of the face define the individuality of the patient and the primary challenge to the reconstructive surgeon is to restore this symmetry and individuality to the patient. Planning a reconstruction so that incision lines fall within the boundaries between these cosmetic subunits will provide the least conspicuous scar. A scar that passes within a single subunit or that crosses lines of demarcation between two subunits can disrupt the natural contour and symmetry of the face and will be most apparent. Adhering to this fundamental principle often means using larger than necessary tissue flaps or resecting extra tissue so that suture lines can be placed within the boundary to avoid disrupting the subunit. Although this technique can be more laborious and may create a larger defect, ultimately it will yield a superior cosmetic result.

Defects that cross boundaries between cosmetic subunits are often best repaired using a combination of flaps (complex repairs) or special suturing techniques (i.e., tacking or suspension sutures) to redefine the disrupted lines of demarcation. Complex repairs and suspension sutures in reconstructive surgery are the primary focus of this chapter.

Functional facial anatomy

A comprehensive knowledge of anatomy is a prerequisite for successful reconstructive or cosmetic surgery. Tissue layers consist of epidermis, dermis, subcutaneous adipose, fascia, and muscle. Each of these layers has its own inherent specific characteristics, but it is the collective contribution of these different layers that contributes to the overall integrity and texture of the skin. In the head and neck, these layers are interconnected through a series of interdigitating adhesions that enable the human face to function as an integrated unit. The activity of specific combinations of facial muscle groups is transferred to the overlying skin through this connective tissue scaffolding and provides the functional capacity to perform complex maneuvers such as eating, drinking, kissing, and speech. These coordinated movements also provide humans with their characteristic ability for emotional expression through complex animated facial movements.

Before embarking upon a discussion of techniques for complex closures, it is pertinent to briefly review the major structural anatomy of the face. The underlying framework of the human face begins with the concrete origins of the bony skeleton. The topography of the cranium consists of prominences and valleys that not only create the aesthetics and individuality of the human face but also serve as key anchoring points for facial muscles. For example, the forehead anchors the frontalis muscle against gravity and enables raising of the brow, the orbital rim provides structural support for the delicate sphincter muscles that protect the orbit, and the malar prominence and zygomatic arch are the anchor points that permit elevation of the upper lip. These and many other key anchoring points provide support for the facial structures, offset the forces of gravitational pull on the face, and permit normal functioning of the facial muscles.

Overlying the cranium and facial muscles is a continuous fascial layer, the SMAS. This layer has attachments to the cranium and invests the facial musculature, forming an interconnected sling that both provides support to the facial structures and acts to integrate the functional activity of facial movements. The SMAS begins in the forehead as a continuation of the galea aponeurotica. It progresses inferiorly, being continuous with the temporalis fascia and zygoma laterally, and with the superficial parotid fascia and malar prominence in the preauricular zone and mid-face, respectively. The SMAS then crosses over the mandible to become continuous with the platysma and inserts into the clavicle, the pectoralis fascia, and sternocleidomastoid fascia of the neck ( Fig. 14.1 ). The SMAS is the unifying structural component of the face linking muscles of facial expression as an integrated network that enables the countless numbers of facial maneuvers. Facial muscles are linked to the SMAS through direct interdigitations, as well as via several well-defined mid-facial ligaments. These connections permit mimetic actions to be transferred to the SMAS and subsequently to the overlying skin.

The functional importance of the SMAS along with an understanding of the major bony attachments of the cranium cannot be overemphasized to the surgeon attempting complex closures of the face. Manipulation of these structures is crucial to overcoming opposing vector forces that resist closure of cutaneous defects to achieve optimal cosmetic results.

Functional skin biomechanics

The heterogeneous cutaneous anatomy contributes to the unique biomechanical properties of skin. Although most of these properties are derived from the dermal collagen and elastin, the subcutaneous fat, blood vessels, and nerves also play a role. Interestingly, the epidermis plays only a small role in skin deformation. Understanding these biomechanical characteristics not only enables the surgeon to choose the best option for a particular defect but also to perform more precise closures.

Unlike other static materials such as steel, skin's stress–strain relationship varies with time. Skin is both viscoelastic and anisotropic, meaning that its “stretchability” is non-linear. Movement of skin is also characterized by its ability to stretch over time (“creep”), and at a certain point in the stress–strain curve to almost completely relax (“stress relaxation”). This quality is most likely because of the breakage of collagen fibers. Although studies have investigated these properties in porcine models, cadavers, and intact human skin rather than incised living skin, the application of these principles to living skin biomechanics during cutaneous surgery has a number of important clinical implications. More recently, the use of computer-generated finite element modeling has increased our understanding of human skin biomechanical properties.

The primary axiom of closing a wound without tension derives from these tissue mechanics. Increased tissue stretch affects the skin's microcirculation, most likely through a combination of narrowing of blood vessel lumina and by causing shear fractures. This tension may also result in venous congestion that can compromise closures. While highly vascularized regions may withstand some degree of tension, poorly perfused areas are susceptible to necrosis. Knowledge of the regional anatomy is critical for understanding the appropriate tissue plane to undermine to reduce tension. Additionally, recognizing that after a certain point, undermining will not reduce closure tension, but will in fact increase the risk of adverse effects such as hematomas or nerve damage, is equally important.

Once the inherent properties and limitations of skin biomechanics are understood, it becomes evident that the properties of time-dependent creep and stress relaxation can be manipulated to aid in the closure of difficult defects. For example, the surgeon can take advantage of these properties when closing a linear defect whose width to length ratio is less than the optimal 1 : 3 proportions (i.e. excessive width). Multiple techniques are often applied to take advantage of the elastic properties of skin. Intraoperative tissue expansion can be performed by a number of methods. The rule of halves may be applied in suturing, with each subsequent stitch leading to a progressive reduction of the tension across the wound. Or initially an interrupted suture or “pulley stitch” may be placed at the center of the wound to reduce tension while the remainder of the wound is closed. With the tension across the wound decreased, buried sutures can be placed more easily and more accurately (see Video 14.1 ). Once the deep layer has been sutured, the pulley stitch is no longer needed and can be replaced by a new layer of epidermal sutures. Alternatively, in many instances, one can begin suturing from one end of the wound toward the opposite pole. By approaching the closure in this manner, the surgeon is taking advantage of sequential wound creep.