Basic plastic surgery techniques and principles: Choosing the right suture material

This is the first article in a new series on basic surgery, inlcuding suturing, and wound management from a plastic surgery point of view. Ben Taylor and Ardeshir Bayat explain how to choose the right suture

Doctors in many different fields regularly close wounds with sutures. You will undoubtedly be called on to suture as you progress in your career; suturing is an important skill for medical students to learn. The many different types of suture available can be daunting, but examples and classifying sutures by their properties can help you to choose the right type.

Suturing is not a new technique but is closely related to the history of medicine. As long as humans have treated wounds, we have looked for a way to close them. The earliest written records date back to ancient India and Egypt, between 1600 bc and 1000 bc, when flax and hemp were used to close wounds. Since then, many materials have been tried including the heads of giant black ants, catgut (sheep intestine), and tree bark. Modern synthetic materials have now replaced most of the older suture materials, but a few remain--such as silk.1

Standard sizes of sutures (with diameters in inches) follow a pattern set at the beginning of the 1900s by the United States Pharmacopoeia.2 A metric system is also used but has yet to gain popularity in the United Kingdom. Sutures were originally sized 0 to 3, but as materials advanced and sutures thinner than 0 were developed, extra 0s had to be added. Today, the scale starts at 3 for the thickest suture then 2/0, 3/0... up to 12/0, which is the thinnest. (See table)

The size of suture should depend on the nature of the repair (table). Generally, to use sutures smaller than 7/0 you need magnification. Thicker sutures should only be used for thicker tissues as they cause more tissue trauma; it is particularly important to use smaller sutures on the face, where bad scarring can be prominent. Smaller sutures have lower tensile strength, however, and can break more easily.

Classifying sutures into groups, depending on how they behave in tissues, makes choosing the right suture material easier (see table below).

Handling--Three properties of a suture affect its handling: memory, elasticity, and knot strength. Some materials have a significant memory--they tend to stay in one position. Memory can lead to difficulty in tying sutures and the knot unravelling. Elasticity is a measure of how a suture returns to its original length after stretching, like a rubber band. An elastic suture will stretch and return to its original length, whereas a labile suture will merely stretch and remain stretched. Elasticity is important when considering oedema of the wound edges during healing. The knot strength is the force needed for a knot to slip--an important consideration when ligating arteries.

Fig 1. Degradation of sutures with time

Tensile strength--The force necessary to break a suture is a measure of its tensile strength. Strength is related to the size of the suture; for the same material, thinner sutures are weaker. The weakest part of a suture is the knot, and so tensile strength applies to the knotted suture. Consideration of strength is important in areas under tension--for example, the linea alba.

Tissue reaction--Tissue reaction is undesirable because it is an inflammatory process and leads to a worse scar. It is maximal between two and seven days after placement.3

Absorbable or non-absorbable--Absorbable sutures degrade naturally in the body (catgut degrades by proteolysis and modern synthetic sutures degrade by hydrolysis).2 Absorbable sutures do not have to be removed--a particularly important advantage in children. Non-absorbable sutures usually have to be removed. In time, absorbable sutures lose their tensile strength (figure 1). Non-absorbable sutures also decay but at a slower rate.

Natural or synthetic--Sutures can be made from natural materials--for example, catgut, silk, or linen. Natural sutures tend to cause an inflammatory tissue reaction. Catgut in particular is unreliably absorbed and loses strength quickly.2 Natural sutures are still useful in some fields--for example, silk in plastic surgery. Catgut is currently unavailable in the United Kingdom owing to concerns about unreliability and risk of infection.

Monofilament or multifilament--Monofilament sutures are single stranded; multifilament sutures are several strands braided together. Braided sutures tend to have better handling characteristics but cause tissue drag, even occasionally sawing through tissues, and the spaces between filaments can harbour bacteria.2 Monofilaments do not have these problems but tend to have significant memory and can be difficult to handle. Figure 2 summarises this.

Magnified picture of multi filament suture

Modern surgical needles are different from sewing needles in one crucial aspect: the thread is actually attached to the needle. The thread is swaged on to the surgical needle--a hole is drilled in the end of the needle and the thread is crimped into place. This reduces the cross sectional area of the needle, which minimises trauma to tissue.2

Needles come in a variety of shapes, and the size depends on the size of the suture you are using. Straight needles are discouraged because of the risk of needlestick injuries. Shapes range from a quarter circle to five eighths of a circle, depending on the how confined the operative site is. J shaped needles are available for working in deep holes.

Needles have either a cutting tip or a round-bodied tip. Cutting tips, as the name implies, have a cutting edge to slice through tough tissues. Round-bodied needles are used in anastomosing blood vessels and intestine because the hole they make is entirely filled by the suture, so that leakage is minimal. Blunt round-bodied needles can be used to pierce fascia, with reduced risk of piercing surgical gloves. Taper cut needles are now available, which combine the penetration of cutting needles, with the benefits of a round-bodied needle.

Ultimately, the type of suture depends on where it is to be used. In the skin, non- absorbable sutures can be used, provided they are removed. Ideally, the suture should be a monofilament. In the face, sutures should be removed as quickly as possible to minimise scarring. A reverse cutting needle penetrates the tissue with minimum force and prevents the needle from cutting out of the skin. Skin trauma is an important issue4 5 and generally sutures around 5/0 are used on the face; the smaller the better. Glabrous skin or skin under tension, however, may need thicker sutures. The consequences of scarring are visible, and in some cases a source of psychological trauma,6 so take every effort to make scars as small as possible, especially in the face.

• use a suture of an appropriate size for the site repair
• a balance between the properties of the suture must be weighed to find the most appropriate suture
• the same job may require a different material under different circumstances
• the choice of suture can be a matter of personal choice

Deeper structures tend to take a long time to heal, are slow to regain tensile strength, and rarely recover completely.7 Ligaments take a long time to recover, and do not fully regain their original strength.8 A non- absorbable or slowly absorbable suture should therefore be used with a blunt needle to maintain these tissues in apposition for a long time.

Fig 2. Summary of suture properties

Other tissues may require repair in different surgical settings. Repair of the perineum is often required after a tear during childbirth. Perineal repairs should use a modern synthetic suture such as polyglactin 910, as a randomised trial showed that it is superior to catgut.9

Abdominal wall closure usually involves two layers.10 A deep mass closure using polydioxanone maintains sufficient tensile strength during repair to splint the wound edges in apposition for long enough to allow healing to take place. As an absorbable suture, it has advantages in not leaving foreign materials inside the wound, but clinical outcomes are the same as when non-absorbable nylon sutures are used.11 Superficial closure usually involves staples.

It is important to close the gastrointestinal tract securely with no leakage. Inverting the edges minimises leakage of contents and minimises adhesions, but everting anastamoses have a reduced incidence of stenosis.12 Maximum strength is achieved in 14-21 days so a medium term suture is used and preferably a monofilament to minimise tissue drag. Round-bodied needles minimise leakage. Tissue reaction should be avoided as it may cause dehiscence.12

When anastomosing blood vessels, a small microsurgical suture should be used to minimise endothelial trauma (which may cause thrombosis)7, with round-bodied needles. Microsurgical sutures are more limited in terms of materials. Ophthalmic procedures require a variety of special needles with spatula points, to minimise damage to other structures in the eye.

Although at first, the range of suture materials available may seem bewildering, it is easy to choose the right material if you first think of what you want the suture to do. There may well be several appropriate options for the task in hand, in which case you must weigh up a balance between the pros and cons of the different materials available. We have designed a flowchart (figure) to help you to find the suture which does what you ask of it.

Ben Taylor, third year medical student, University of Manchester
Email: bentaylor@doctors.org.uk

Ardeshir Bayat, specialist registrar in plastic surgery, University of Manchester
Email: ardeshirbayat@hotmail.com


studentBMJ 2003;11:131-174 May ISSN 0966-6494

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