Sutures are specialized medical devices used to hold body tissues together after an injury or surgical incision to promote healing. These materials, commonly known as stitches, provide temporary mechanical support until the wound is strong enough to withstand natural stresses. While their function is straightforward, sutures are manufactured in a vast array of forms, materials, and colors. The choice of which suture to use depends on the tissue being closed, the tension on the wound, and the required duration of support.
The Role of Color in Suture Identification
The color of a suture thread is primarily a visual aid for the surgeon and surgical team, enhancing contrast against the surrounding biological tissue. This color coding helps in quickly identifying the suture material type, especially when multiple kinds are used during a complex procedure. Violet or purple is a common dye used for synthetic absorbable sutures, such as those made from polyglactin 910 (Vicryl) or polydioxanone (PDS), helping to distinguish them from non-absorbable varieties. Conversely, a bright blue is frequently used to color non-absorbable synthetic sutures like polypropylene (Prolene) and nylon, which is particularly useful when closing pale skin or other light-colored tissues.
Material Types and Absorption Properties
While color aids identification, the fundamental classification of sutures is based on their material composition and how they behave within the body. Sutures are either absorbable, meaning they are designed to break down naturally, or non-absorbable, requiring manual removal or remaining permanently embedded.
Absorbable sutures are typically made from either natural materials, like purified animal collagen (catgut), or synthetic polymers. Synthetic absorbable materials, such as polyglactin 910 (Vicryl) and poliglecaprone 25 (Monocryl), are broken down through hydrolysis, where water in the tissue gradually dissolves the polymer chains. The absorption time varies significantly; for example, polyglactin 910 loses most of its strength within three weeks, while polydioxanone (PDS) provides support for much longer, sometimes up to six months.
Non-absorbable sutures are used when extended or permanent wound support is necessary, such as in cardiovascular procedures or for repairing slow-healing tissues like fascia or tendons. These threads, which include materials like nylon, polypropylene, and silk, resist degradation and maintain their tensile strength indefinitely. They are commonly used for skin closures that are removed after a week or two, or in high-tension areas where long-term reinforcement is required.
Structure, Gauge, and Clinical Context
Beyond color and material, sutures are classified by their physical structure, which profoundly impacts their handling and biological interaction.
A monofilament suture consists of a single, solid strand that passes smoothly through tissue with minimal friction, reducing the risk of inflammation. However, these single strands are generally stiffer and can require more knots to achieve adequate security.
Conversely, multifilament sutures are made of several fine filaments twisted or braided together, such as in silk and polyglactin 910. The braided structure provides superior flexibility, better handling, and excellent knot security. A key drawback is that the microscopic spaces between the fibers can harbor bacteria, making them a less favorable choice for contaminated wounds.
Suture size is standardized using the United States Pharmacopeia (USP) gauge system, which measures the thread’s diameter. The sizing is counter-intuitive: a suture labeled 6-0 is much finer than a 3-0, as more zeroes indicate a smaller diameter. Surgeons select the smallest gauge that provides sufficient tensile strength for the tissue being closed, balancing wound support with minimal tissue trauma.