Suture materials

The different types and ideal properties of sutures at described in Tables 49.5 and 49.6.

A suture can be chosen with different properties in mind a follows.

Absorbable

Catgut is the oldest suture material known and is made from the submucosa of sheep intestines. It can be chromic or plain and is still the most frequently used suture material for intestinal anastomoses.

Suture material is absorbed in one of two ways. The first applies to catgut and collagen where the absorption mechanism is by enzymatic digestion. The other method is one of preliminary hydrolysis which is the effect of water on the suture material and does not require the same cellular involvement as does catgut with its proteolytic digestive enzymes. Hydrolysis is increased with rise in temperature or pH changes. Figure 49.23a demonstrates in general terms the comparative absorption times for catgut, Dexon (homo­polymer of glycolide), Vicryl (copolymer of glycolide and lactide) and PDS (polydioxanone). Once a suture has been broken up by hydrolysis, polymorphonuclear cells and other macrophages (e.g. giant cells) can digest even so-called unabsorbable material. As the material absorbs it loses its tensile strength (Fig. 49.23b).

Delayed or nonabsorbable

Very few sutures are truly completely nonabsorbable. Silk is derived from the cocoon of the silkworm larva. The suture is braided round a core and coated with wax to reduce capillary action. Tissue reaction is greater than to the synthetic nonabsorbables because silk is a foreign protein. For this reason silk is not now used in anastomoses, and most surgeons prefer to use a monofilament synthetic suture if a nonabsorbable suture is deemed necessary. Wire sutures are ideal for qualities of inertness and permanence but working with them is difficult and they are virtually absolete.

Staples

Circular, linear and linear-cutting stapling devices are used to form anastomoses. The devices carrying these staples can be disposable or reusable. Until 1986 the staples were always nonabsorbable, being made of stainless steel. However, absorbable staples have now been developed. The circular stapling device is used for oesophageal and rectal anastomoses. Their use is not a short cut to the joining of two pieces of intestine. The preparation of the bowel ends and the placement of the purse-string sutures must be carefully executed. They do, however, help in situations where the placement of sutures can be difficult, e.g. a low colorectal or anal anastomosis in a patient with a narrow pelvis (Fig. 49.6).

Linear stapling for anastomoses may leave awkward edges and ends (Fig. 49.6). Linear-cutting staplers can save time if very long closures or multiple anastomoses are necessary but have little benefit over hand-sutured anastomoses.

It is necessary to choose suture material that has the best characteristics for carrying out an anastomosis in a particular site. Vascular anastomoses require fine suture materials with minimal tissue reaction — strength is a secondary considera­tion — and Prolene is commonly used. Gut anastomoses require sutures with good handling qualities with secure knotting; pliancy is also important, as is strength when the intestine begins to contract. Plain catgut is unsuitable for intestinal anastomoses, but chromic catgut can be used for gastric and small intestinal unions. Rectal and oesophageal anastomoses should employ unabsorbable, or long-delayed absorbable sutures (e.g. PDS), because these areas combine many adverse factors with the requirement to withstand powerful contractile activity.