An Introductory Guide to Suture Types

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Harri Foster Davies The needle curvature describes how tightly the needle curves. Common measurements include: • Straight – designed to be used by hand; mostly used for skin closure or microsurgical procedures. • Half-curved (ski) – used in laparoscopic surgery. • 1/4 circle - a shallow curve and is used on easilyaccessible convex surfaces, for instance, in ophthalmic and microsurgical procedures. • 3/8 circle – the most commonly needle curvature; easy to manipulate in large/superficial wounds. • 1/2 circle – suitable for confined locations. • 5/8 circle – ideal for deep confined holes. 3. Needle Body and Points Needles either have round bodies or triangular-shaped bodies. • Round-bodied needles pierce and spread tissues with minimal cutting. They have either sharp (taper-point) or blunt points. o Taper-point - used in easily-penetrated tissues (e.g. abdominal viscera). o Blunt - used to dissect through friable tissues (e.g. liver, kidney). • Needles with triangular-shaped bodies are referred to as “cutting” needles. They are used to penetrate tough tissues. They are either ‘conventional’ or ‘reverse’. o “Conventional” cutting needles have the cutting edge on the inside arc of the needle and are useful for skin and sternum. o “Reverse” cutting needles have their cutting edge on the outside arc of the needle and are ideal for tough tissue like skin, tendon sheath, or oral mucosa. Reverse cutting needles have a reduced risk of tearing through tissues compared to conventional cutting needles since tension is not in the same vector as the cutting edge. These types of needles are typically used in ophthalmic and cosmetic surgery, where minimal trauma is paramount. Suture Thread The ideal suture: Sterile; small as possible whilst providing high, uniform tensile strength; consistent uniform diameter; appropriate pliability; provides knot security; low bioreactivity. The choice of suture material is based on the balance of certain characteristics. Such characteristics can be grouped into 4 categories: Physical, Handling, Biocompatibility, and Biodegradation. • Physical characteristics include size (diameter), number of filaments, tensile strength, elastic modulus, bending stiffness, stress relaxation, and coefficient of friction. • Handling characteristics include pliability, packaging memory, knot tiedown, knot slippage, and tissue drag. • Biocompatibility characteristics include inflammation, wound infection risk, thrombus formation risk, carcinogenicity, and allergenicity.
Harri Foster Davies • Biodegradation characteristics include absorbability, as well as the biocompatibility of any breakdown products. 1. Suture Size There are two classification systems: USP (United States Pharmacopeia) and the European system. The USP grading is calculated using not only diameter, but also tensile strength and knot security. The European system uses only the diameter of the suture in millimetres. As suture material is a foreign substance, it will cause inflammation. This tissue reaction will continue until the suture material is absorbed or encapsulated by fibroblasts. The smaller the suture diameter, the less the tissue reaction due to decreased presence of foreign material. However, the smaller the diameter, the weaker the tensile strength. As a general rule, the smallest suture material that properly holds tissues should be used. 2. Suture Filaments Suture strands can either be monofilament, braided, or twisted. • Monofilament sutures are formed from one strand. They have a lower infection risk and create less drag when passing through tissues. However, they have a lower ease of handling and knot strength. They can also crimp easily, resulting in weak spots that lessen tensile strength. • Multi-filament sutures are comprised of several strands braided or twisted together. They provide increased tensile strength and pliability but also increase drag within tissues. Multi-filamentous sutures can be coated with materials that lessen the drag and make knots easier to slide into place (but this then results in poor knot security). 3. Suture Material Suture material can be classified as absorbable or non-absorbable. Types of absorbable suture include: • Gut – a natural monofilament suture. Often used for internal soft tissue. The body has a strong reaction to this suture material which often results in encapsulation. Not commonly used outside gynaecological surgery. • Polydioxanone (PDS) – a synthetic monofilament suture. Used for many types of soft tissue wound repair (such as abdominal closures) as well as for paediatric cardiac procedures. • Poliglecaprone (Monocryl) – a synthetic monofilament suture. General use in soft tissue repair. Most commonly used to discretely close skin. • Polyglactin (Vicryl) – a synthetic braided multi-filament suture. Good for repairing hand or facial wounds. The absorbability of a suture is determined by the material it is made from and the number of strands that comprise that suture. Natural suture will be degraded by enzymes whilst synthetic suture will be degraded through hydrolysis (i.e. water gradually penetrates the suture filaments, causing breakdown of the suture’s polymer chain). Types of non-absorbable suture include: • Silk – a natural braided suture.
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An Introductory Guide to Suture Types

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