Choosing the right suture material

The ideal suture would be totally biologically inert and cause no tissue reaction. It would be very strong but simply dissolve in body fluids and lose strength at the same rate that the tissue gains strength. It would be easy for the surgeon to handle and knot reliably. It would neither cause nor promote complications. Whilst there have been very great improvements in suture materials in the recent past and modern sutures are very close to above ideal, no single suture is ideal in all circumstances.

Different tissues have differing requirements for suture support, some needing only a few days eg muscle, subcutaneous tissue, skin; whilst others require weeks or even months eg fascia and tendon. Vascular prostheses require longer term, even permanent support. The surgeon must be aware of the differences in the healing rates of various tissues when choosing a suture material. Individual patient variation further complicates the decision. Healing of wounds is delayed by a range of factors such as infection, debility, respiratory problems, obesity, collagen disorders, malnutrition, malignancy, drugs eg cytotoxics and steroids. The surgeon wants to ensure that a suture will retain its strength until the tissue regains enough strength to prevent separation. Some tissues heal slowly and may never regain preoperative strength. Some may be placed under natural tension such as a tendon repair so the surgeon will want suture material that retains strength for a long time. In rapidly healing tissue, the surgeon may use a suture that will lose its tensile strength at about the same rate as the tissue gains strength and that will be absorbed by the tissue so that no foreign material remains in the wound. With all sutures, acceptable surgical practice must be followed with respect to drainage and closure of infected wounds. Excess tissue reaction to the suture encourages infection and slows healing. When taking all these factors into account, the surgeon has several choices of suture material available. Subjective preferences such as familiarity with the material and availability need also to be taken into account. source

Contents

Absorbable and Non-absorbable

Sutures can conveniently be divided into two broad groups : absorbable and non absorbable. Regardless of its composition, suture material is a foreign body to human tissue and will elicit a foreign body reaction to a greater or lesser degree. Two major mechanisms of absorption result in the degradation of absorbable sutures. Sutures of biological origin such as surgical gut are gradually digested by tissue enzymes. Sutures manufactured from synthetic polymers are principally broken down by hydrolysis in tissue fluids and are preferred. Non absorbable sutures, made from a variety of non biodegradable materials, are ultimately encapsulated or walled off by fibroblasts.

Non absorbable sutures ordinarily remain where they are buried within the tissues. This can cause late complications such as the development of gall stones around non-absorbable sutures in the common bile duct or bladder stones in the urinary bladder. In these situations it is best to use absorbable materials. Improvements in absorbable sutures mean that they can be used in a variety of situations where previously surgeons would have recommended non-absorbable materials. Polyglycolic acid is used for bowel anastomosis in place of silk and polyglactin is used in closure of the abdominal muscles in place of nylon or prolene. It could be said that it is always best to use an absorbable suture unless there is a good reason not to. When used for skin closure, non-absorbables must be removed or they will lead to chronic sepsis.

Absorbable sutures

Natural

Synthetic

Chemical polymers are absorbed by hydrolysis and cause a lesser degree of tissue reaction following placement.

The examples listed above represent only some of the available synthetic absorbable sutures. Depending on anatomic site, surgeon's preference, and the required suture characteristics, other types of synthetic absorbable suture are available.

Nonabsorbable sutures

Natural

Cutting, tearing, or pulling other patient tissues is also a risk. Surgical steel in the presence of other metals or alloys may cause electrolytic reactions and, therefore, is not a safe choice in these circumstances. The size of the steel wires is classified by the Brown & Sharpe gauge, ie, 18 (largest diameter) to 40 (smallest diameter). Standard United States Pharmacopeia classification is also used to denote wire diameter.

Synthetic

Monofilament and Multifilament

A further subdivision of suture materials is Monofilament and Multifilament. A monofilament suture is made of a single strand. It resists the harboring microorganisms and it ties smoothly, which can ease the judgment of the tightening of a knot but can also lead to knot slippage. A multifilament suture consists of several filaments twisted or braided together. This gives good handling and tying qualities.

Natural and synthetic

Natural sutures such as silk and catgut are largely being replaced by synthetic materials. There is a case for suggesting that they should no longer be used.

Suture diameter and strength

The sizes and tensile strengths for all suture materials are standardized by U.S.P. Regulations. Size denotes the diameter of the material. Stated numerically, the more zeroes in the number, the smaller the size of the strand. 00000 is referred to as 5-0 for example which is smaller than a size 4-0. The smaller the diameter, the less tensile strength. Tensile strength of a suture is the measured pounds of tension that the strand will withstand before it breaks when knotted. To avoid an excess tissue reaction the surgeon should choose the smallest diameter suture with sufficient strength for the task.

Some typical examples

Polyglactin (coated vicryl) is braided. It is commonly used for bowel anastomosis, as a general tie for vessels and as a subcuticular suture for skin. It has 75% of its strength at 2 weeks and 50% at three weeks. It causes a minimal tissue reaction and is very close to being the ideal suture for almost all purposes. A more rapidly absorbing version (Vicryl Rapide) is now produced which loses all strength within 14 days.

Polydioxanone (PDS) is monofilament. It absorbs slowly and there is minimal absorption until about 90 days. However, its in vivo tensile strength reduces more quickly to 70% at 2 weeks, 50% at four weeks and 25% at six weeks. It is widely used for abdominal wall muscle closure where is has replaced nylon/prolene as it does not cause chronic suture sinuses which occur with non-absorbable materials.

Nylon (eg ethilon) is a synthetic monofilament material widely used for skin suture. Polypropylene (prolene) is often preferred to nylon as it is thought to be slightly more inert. It is widely used for abdominal wall closure.