Approximation refers to bringing the sides of a wound into precise, close contact with one another. This state, known as approximated wound edges, is the ideal goal for most surgical incisions and acute traumatic laceration repairs. When edges are approximated, the tissue layers are carefully aligned and secured to facilitate the most efficient form of tissue regeneration.
Defining Wound Edge Approximation
Approximation is the physical act of aligning the various tissue layers, including the epidermis, dermis, and subcutaneous tissue, to eliminate space between the wound sides. This alignment is necessary for healing by “primary intention,” which is the fastest and most desirable method of wound repair. Primary intention occurs in clean wounds with minimal tissue loss, such as a surgical incision.
On a cellular level, approximation dramatically reduces the distance new cells must travel to bridge the injury. The proper alignment of deep tissue layers, often achieved with buried sutures, is crucial to prevent “dead space.” Dead space is a pocket beneath the skin surface where blood or fluid can collect, which impedes healing and increases infection risk.
A properly approximated wound appears slightly everted, meaning the skin edges are gently turned outward rather than inverted or depressed. This slight eversion ensures the deepest layers of the skin are in contact and prevents the final scar from appearing sunken.
The Primary Goal of Approximation
The purpose of approximating wound edges is to accelerate the healing process by creating the shortest possible pathway for tissue repair. Minimizing the wound surface area allows the body to focus resources on rebuilding connective tissue across a tiny, well-defined line. This efficiency results in a swift progression through the inflammatory, proliferative, and remodeling phases of wound healing.
Approximation also reduces the risk of infection. A closed wound provides a physical barrier that prevents external pathogens from entering deeper tissues.
A key benefit is the minimization of scar formation. When wound edges are closely brought together, the amount of new connective tissue, primarily collagen, needed to bridge the gap is small. This limited tissue deposition results in a thin, neat line, often referred to as a linear scar, which is less noticeable than the wide, thick scar that forms when a wound heals without approximation.
Techniques Used for Closure
Medical professionals use several methods to hold wound edges in approximation, chosen based on the wound’s depth, location, and tension.
Sutures and Staples
Sutures, or stitches, are the most traditional and versatile method, securing the edges together using a needle and thread. Deep, absorbable sutures are often placed below the skin surface to eliminate dead space and reduce tension on the outer layer. Non-absorbable sutures are used to hold the epidermis together.
Surgical staples offer a faster alternative, particularly for long incisions, by clamping the skin edges together with a metal wire for strong mechanical closure. Staples are generally not favored where cosmetic appearance is a high concern, as they can sometimes lead to small puncture marks.
Adhesives and Strips
For superficial wounds with low tension, less invasive techniques are employed. Tissue glue, a sterile liquid adhesive, is applied directly over the approximated wound edges and polymerizes quickly, creating a strong, flexible seal. Adhesive strips, commonly known as Steri-Strips, are reinforced tapes placed across the wound to provide support and keep the edges aligned.
Healing Without Approximation
When wound edges cannot be brought together, the tissue must heal through “secondary intention.” This occurs in wounds with significant tissue loss, such as large abrasions, pressure ulcers, or infected wounds that must be left open to drain.
The body fills this open space from the bottom up with specialized tissue called granulation tissue. Granulation tissue is a mix of new blood vessels, immune cells, and connective tissue that slowly builds up until the defect is filled. This method requires significantly more time and energy compared to primary intention healing.
The final result of secondary intention healing is a larger, more pronounced scar due to the extensive amount of granulation and subsequent scar tissue required. The open nature of the wound also leaves the area susceptible to infection for a longer duration.