Basic Suturing

The goals of wound closure include obliteration of dead space, even distribution of tension along deep suture lines, maintenance of tensile strength across the wound until tissue tensile strength is adequate, and approximation and eversion of the epithelial portion of the closure. Methods for mechanical wound closure include staples, tape, adhesive, and sutures. Each method has specific indications, advantages and disadvantages, and special considerations.The subject of this article is the suture closure of wounds. Similar to other methods of wound closure, suture closure permits primary wound healing. Tissues are held in proximity until enough healing occurs to withstand stress without mechanical support. An extensive review of wound healing and the factors that influence this process are available elsewhere (eg, see the eMedicine articles Incision Placement; Wound Healing, Nerve; and Wound Healing, Skin).
Suture material is a foreign body implanted into human tissues; it elicits a foreign body tissue reaction. During wound closure, a sterile field and meticulous aseptic technique are critical to minimize the risk of wound infection. Other complications of wound healing, such as hypertrophic scars, wide scars, and wound dehiscence, may result from patient factors (eg, nutritional status), incorrect suture selection, or a technique that results in excessive tension across the wound.
Skillful wound closure requires not only knowledge of proper surgical techniques but also knowledge of the physical characteristics and properties of the suture and needle. The goal of this article is to review the types of sutures and needles for wound closure and to discuss principles that influence suture and needle selection.
For excellent patient education resources, visit eMedicine's Procedures Center. Also, see eMedicine's patient education article Suture Care.

Suture Qualities

Ideal suture characteristics

The ideal suture has the following characteristics:

• Sterile
• All-purpose (composed of material that can be used in any surgical procedure)
• Causes minimal tissue injury or tissue reaction (ie, nonelectrolytic, noncapillary, nonallergenic, noncarcinogenic)
• Easy to handle
• Holds securely when knotted (ie, no fraying or cutting)
• High tensile strength
• Favorable absorption profile
• Resistant to infection

Unfortunately, at present, no single material can provide all of these characteristics. In different situations and with differences in tissue composition throughout the body, the requirements for adequate wound closure require different suture characteristics.

Essential suture characteristics

All sutures should be manufactured to assure several fundamental characteristics, as follows:

• Sterility
• Uniform diameter and size
• Pliability for ease of handling and knot security
• Uniform tensile strength by suture type and size
• Freedom from irritants or impurities that would elicit tissue reaction

Other suture characteristics

The following terms describe various characteristics related to suture material:

• Absorbable - Progressive loss of mass and/or volume of suture material; does not correlate with initial tensile strength
• Breaking strength - Limit of tensile strength at which suture failure occurs
• Capillarity - Extent to which absorbed fluid is transferred along the suture
• Elasticity - Measure of the ability of the material to regain its original form and length after deformation
• Fluid absorption - Ability to take up fluid after immersion
• Knot-pull tensile strength - Breaking strength of knotted suture material (10-40% weaker after deformation by knot placement)
• Knot strength - Amount of force necessary to cause a knot to slip (related to the coefficient of static friction and plasticity of a given material)
• Memory - Inherent capability of suture to return to or maintain its original gross shape (related to elasticity, plasticity, and diameter)
• Nonabsorbable - Surgical suture material that is relatively unaffected by the biological activities of the body tissues and is therefore permanent unless removed
• Plasticity - Measure of the ability to deform without breaking and to maintain a new form after relief of the deforming force
• Pliability - Ease of handling of suture material; ability to adjust knot tension and to secure knots (related to suture material, filament type, and diameter)
• Straight-pull tensile strength - Linear breaking strength of suture material
• Suture pullout value - The application of force to a loop of suture located where tissue failure occurs, which measures the strength of a particular tissue; variable depending on anatomic site and histologic composition (fat, 0.2 kg; muscle, 1.27 kg; skin, 1.82 kg; fascia, 3.77 kg)
• Tensile strength - Measure of a material or tissue's ability to resist deformation and breakage
• Wound breaking strength - Limit of tensile strength of a healing wound at which separation of the wound edges occurs

Suture size

The United States Pharmacopeia classification system was established in 1937 for standardization and comparison of suture materials, corresponding to metric measures. The 3 classes of sutures are collagen, synthetic absorbable, and nonabsorbable. Size refers to the diameter of the suture strand and is denoted as zeroes. The more zeroes characterizing a suture size, the smaller the resultant strand diameter (eg, 4-0 or 0000 is larger than 5-0 or 00000). The smaller the suture, the less tensile strength of the strand.