SURGICAL SUTURES AND LIGATURES

Surgical sutures and ligatures are threads or strings specially prepared and sterilized for use in surgery. The former one is used for sewing tissues etc. together and the later one for tying blood vessels and other tissues.

Different type of materials are in use for these purposes. They are intestinal tissues and tendons of a large assortment of animals and birds, various kind of thread spun from vegetable fibers, human hair, horse and camel hair, synthetic threads and metallic wire.

These materials may be divided into two principal classes :

Absorbable and Non-absorbable type.

In the former type are found those materials that are absorbed or digested in the tissues in the body after their suturing or ligaturing function has been performed and, provided the material is non irritant and sterile, may be left in the body with confidence.

Examples: Animal intestine and other tissues.

Catgut, the classic absorbable suture derived from collagen rich animal tissue (usually using selective layers of sheep intestine) , is proteinacious in nature and it appears that certain proteolytic enzymes in tissues are responsible for the digestion of catgut and its disappearances from the wound area.

The later type since insoluble/not digested or not absorbed in the body, their use will depend among other things, non irritant properties. They may disintegrate after a long period but commonly become encysted without causing any problem.

Surface stitches using non absorbing materials bind the edges of a wound and are removed after healing has taken place.

Essential Properties of Sutures and ligatures.

• They must be sterile.

• Their strengths must be adequate for the purpose for which they are used.

• They must not cause any irritation as far as practicable.

• Their gauge should be as fine as possible.

• If absorbable, approximate time of absorption should be known.

Measurements of in-vivo degradation of sutures and ligatures generally separate them into two classes.

• Sutures that undergo rapid degradation in tissues losing their tensile strength within 60 days are considered absorbable sutures.

• Those that retain their tensile strength for longer than 60 days are non absorbable sutures/ligatures.

• This terminology is somewhat misleading because even some non absorbable sutures (e.g. silk, cotton and nylon) lose some tensile strength during 60 day interval. Investigation on the tensile strength of implanted non absorbable sutures during a period of two years revealed that silk lost approximately 50% of its original strength in one year and had no strength at the end of two years. Cotton lost 50% of its strengths in six months, but still had 30-40% of its original strength at the end of two years. Nylon lost approximately 25% of its original strength throughout the two year observation period.

Modern chemistry has developed a variety of synthetic fibers from polyamides (nylon), polyesters, (Dacron), polyolefins (polyethylene,polypropylene), polytetrafluoroetylene, to polybutyl ester.

New forms of absorbable sutures based upon synthetic polyesters such as polyglycolic acid , co-polymers of lactide and glycolide, polydioxanone, co-polymers of glycolide and caprolactide and a blend of glycolide, trimethylene carbonate, and dioxanone have been introduced as alternative absorbable materials.

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 as has already been indicated.

Sutures manufactured from synthetic polymers are principally broken down by hydrolysis in tissue fluids and are preferred.

Non absorbable sutures are, in like manner, sutures that are not dissolved or decomposed by the body’s natural action. Such sutures are generally not naturally occurring materials (with the exception of silk). Some (silk and nylon) while being classified as non absorbable actually dissolve after a prolong period of time compared to that of absosrbable materials.

A further subdivision of suture materials is Monofilament and Multifilament.

A monofilament suture is made of a single strand. It resists the harboring of micro-organisms and it ties smoothly, which can ease the judgement of the tightening of a knot but can also lead to knot slippage.

A multifilament suture consists of several filaments twisted or braided together.

Sutures are manufactured with a wide variety of parameters. They can be mono filament or multi filaments twisted together, spun together or braided. They can also be dyed, un dyed, coated, not coated.

With the goal of understanding the effects of so many variations of suture type, the properties and material of which they are composed are and have been studied in depth. The use of sutures is one of the most common practices in the medical field and thus has direct effect on a majority of the world’s population.

As there are several different suture materials and needles that provide an accurate and secure approximation of the wound edges, ideally, the choice of the suture material should be based on the biological interaction of the materials employed, tissue configuration, and the biochemical properties of the wound. The tissue should be held in apposition until the tensile strength of the suture is sufficient to withstand stress.

A common theme of many reportable investigations is that all biomaterials placed within the tissue, damage the host defenses and invite infection. Since surgical needles have a proven role in spreading deadly blood borne viral infection, the surgeon must select appropriate gloves, needles and sutures that reduce significantly the risk of accidental injuries during surgery.

Three important considerations in wound closure are

– A) The type of suture,

– B) The tying technique and

– C) The configuration of the suture loops.

• Selection of a surgical suture material is based on its interaction with the wound and its mechanical performance in vivo and in vitro.

LIST OF MANY OF THE COMMERCIALLY AVAILABLE TYPES OF SUTURES:

1. Cellulose based (cotton),

2. Protein cellulose (silk),

3. Processed collagen (catgut),

4. Nylon,

5. Polypropylene,

6. Aramid,

7. Polyglycolic acid (Dexon*),

8. Polyesters,

9. Polytetrafluoroethylene,

10. Steel,

11. Copper,

12. Silver,

13. Aluminum,

14. Various alloys,

15. Ticron*

16. Ethilon*

17. Prolene*

18. Ethiflex,

19. Polygalactin 910

20. Polyglycolide-lactide polymer (Vicryl*)

21. Polydioxanone (PDS*)

22. Polyglecaprone 25 (Monocryl*)

23. Polyglyconate (Maxone)

24. Ethibond

According to the Medical Device Amendments Act of Federal Food, Drug and Cosmetic Act, 1976 several sutures used in practice have been reclassified from class III to class II.

According to U.S.P. (27th Edn.) non absorbable suture is classified and typed as follows:

• Class-I is composed of silk or synthetic fibers of monofilament, twisted or braided construction where the coating if any, does not significantly affect thickness (e.g. braided silk, polyester or nylon; monofilament nylon or polypropylene).

• Class-II is composed of cotton or linen fibers or coated natural or synthetic fibers where the coating significantly affects thickness but does not contribute significantly to strength (e.g. virgin silk suture).

• Class-III suture is composed of monofilament or multifilament metal wire.

The U.S.P. is one of the official compendium for the suture industry. It sets standards and guidelines for suture manufacture. Suture sizes are given by a number representing diameter ranging in descending order from 10 to 1 and then 1-0 to 12-0, 10 being the largest and 12-0 being the smallest at a diameter smaller than a human hair.

Suture sizes and Tensile strength:

• The sizes and tensile strengths for all sutures are standardized by U.S.P. regulations. Size denotes the diameter of the material (mm) and the tensile strength in Newton.

• 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 is tensile strength. Tensile strength of the suture is the tension that the strand will withstand before it breaks when knotted.

• The use of various dimension of the sutures is very much dependent on the location, of the injury, type of protection needed etc. etc.

Reason / reasons for hardening of surgical sutures composed of purified connective tissue and their packaging:

• Occasionally, such surgical sutures are required to be hardened using appropriate techniques (usually using chromic salts, such as chromium trioxide) so as to delay the absorption of the suture materials in the body whenever they are used. Surgical sutures obtained from such sources are packaged in glass tubing. The tubes may contain some fluids in it.

• When the tubing fluid contains any water the tubes of the catgut are labeled “Non-boilable”.

• If the tubing fluid is anhydrous, the tubes may be boiled before opening for its use in reality.

• Non boilable tubes are filled with alcohol containing small quantity of water.

• Official catgut is of the non boilable variety.

Sterilization Techniques used and its implications on the suture materials.

• Among the widely accepted methods for the sterilization of sutures, autoclave sterilization with free access of water vapor, applicable only for those sutures that

are not harmed by this process. Dry heat at 310º F ; ethylene oxide ; and irradiation sterilization using either β or γ rays.

Advantages of irradiation sterilization over the older methods insofar as commercial production is concerned.

• The sutures are sterilized in their final sealed packages, eliminating any danger of recontamination.

• The radiation dose is considered to be 40% greater than necessary to kill even the most resistant spore forming organisms, each suture receiving a minimum dose of 2.5 mega rads.

• Lack of deteriorating effect upon many sutures.

• Irradiation sterilized surgical gut is stronger, more pliable and easier to handle than dry heat sterilized surgical gut sutures.

• In the irradiation process the prepared gut is packed in aluminum foil envelopes containing 90% isopropyl alcohol as preservative. The envelopes are then passed through an irradiation area on a conveyer system. Thus the catgut is sterilized when sealed in its final container and since the process is rapid, there is no lengthy hold up of material as in other processes. The exterior of the packet is sterilized before opening by immersion in a solution of 1% formaldehyde in 90% isopropyl alcohol.