Key Practice Points
The most important layer of skin for wound closure is the tough dermis. It is the “anchor” for sutures.
Proper and careful apposition of the wounded dermis will bring the lacerated outer layer of skin, the thin epidermis, together for the best cosmetic result.
The superficial fascia, or subcutaneous fatty tissue, lies just below the dermis. Because nerve fibers travel in the subcutaneous layer below and into the dermis, this fatty layer is the preferred site for delivery of local anesthetics.
Débridement of dermis should be judicious and limited, whereas for subcutaneous fat it can be liberal.
Lacerations and incisions parallel to skin tension lines leave thinner and less visible scars than those that cross these lines.
Age and use of corticosteroids weaken skin and make it thinner. Repairing lacerations and wounds to this skin is a challenge.
The primary anatomic focus in surface wound care is the skin. Underlying the skin are two equally important structures, the superficial (subcutaneous) fascia and the deep fascia. The fasciae not only act as a supportive base to the skin but also carry nerves and vessels that eventually branch into the fasciae. All the layers of the skin and fascia are present in every body site, but they vary considerably in thickness. Most skin is 1 to 2 mm thick, but thickness can increase to 4 mm over the back. This variability often dictates the choice of suture needles. Larger, stronger needles are required to penetrate the skin on the palms of the hands and the soles of the feet. Small, delicate needles should be used on the thin skin of the eyelids.
Anatomy of the Skin and Fascia
Although the skin and fascia comprise a complex system of organs and anatomic features, it is the layer arrangement that is most important for wound closure ( Fig. 3-1 ). These layers include the epidermis, dermis, superficial fascia (commonly referred to as the subcutaneous or subcuticular layer), and deep fascia. These layers should be thought of as planes that need to be carefully and accurately reapproximated when disrupted by trauma. Each one has its own set of characteristics that are important to proper wound closure and healing.
Epidermis and Dermis (Skin or Cutaneous Layer)
The epidermis is the outermost layer of the skin. The epidermis consists entirely of squamous epithelial cells and contains no organs, nerve endings, or vessels. Its primary function is to provide protection against the ingress of bacteria and toxic chemicals and the inappropriate egress of water and electrolytes. This is the outermost, visible layer and gives skin its final cosmetic appearance.
Although the epidermis is an anatomically separate layer, it is only a few cell layers thick. During wound repair, it cannot be seen by the naked eye as separate from the dermis. Correct approximation of the epidermis naturally results from careful apposition of the lacerated edges of the dermis.
The dermis lies immediately beneath the epidermis. It is much thicker than the epidermis and is composed primarily of connective tissue. The main cell type in the dermis is the fibroblast, which elaborates collagen, the basic structural component of skin. The deeper dermis contains the bulk of adnexal structures of the skin. These include the hair follicles and vascular plexus. Nerve fibers branch and differentiate into specialized nerve endings that reside in the dermis.
The dermis is the key layer for achieving proper wound repair. It is easily identifiable and provides the anchoring site for percutaneous and deep sutures ( Fig. 3-2 ). Every effort is made to cleanse, remove debris, and accurately approximate the dermal edges to allow for optimal wound healing with minimal scar formation. If dermis is devitalized or severely damaged, sharp débridement often is necessary to remove it. Tissue excision and trimming must include only that which is truly unsalvageable, however. Because dermal defects are replaced by scar tissue, any unnecessary dermis removal increases the size and prominence of that scar.