Surgical Sutures

Surgical suture is a medical device used to approximate body tissues after an injury or surgery or to ligate blood vessels. Sutures must be easy to handle; have high tensile strength and should permit secure holding of the knot. It should be biocompatible, nontoxic and inert. Knowledge of physical characteristics of sutures is important for surgeons, in order to choose the right suture material.

The choice of suture material depends on the following considerations.

• Type of tissue to be closed.
• Anatomic site.
• Type of procedure.
• Intended use of suture.
• Amount of tension on the wound.
• Number of layers of closure.
• Depth of suture placement.
• Anticipated amount of edema.
• Anticipated timing of suture removal.

General guidelines for selection of sutures

• Smallest diameter suture adequate to hold the tissue should be used to minimize tissue trauma and to reduce the amount of foreign material inside the body.
• Tensile strength should be sufficient to hold the tissue, but should not exceed the tensile strength of the tissue.
• Monofilament sutures are preferable as they cause less tissue trauma and have lesser incidence of infection.
• Absorbable sutures preferred for suturing of tissues inside the body, removable nonabsorbable sutures preferred for suturing of skin.
• Synthetic absorbable sutures preferable over natural absorbable sutures as they cause less tissue reaction.

History

Earliest records of sutures use were from Egypt in 3000 BC. Oldest suture was found in a mummy from 1100 BC. Indian sage Sushrutha in his treatise called Susruthasamhitha described use of sutures in 500 BC. In ancient cultures, live ants and beetles were allowed to bite to close the wounds and the body of the insect was cut off keeping the head as a suture material. Silk, cotton and dried intestines of sheep or cattle (catgut) were other natural materials used as sutures.

Till the 1930s, catgut made from dried and treated intestines of sheep or cattle was the main suture material used. Sterilization of catgut using phenol, introduced by Joseph Lister in the 1860s was another milestone in the history of sutures. Synthesis of nylon in 1938 heralded the arrival of modern sutures. In the 1960s, absorbable synthetic materials such as polyglycolic acid and polylactic acid were introduced.

Classification

Sutures can be classified into absorbable and nonabsorbable. These can be subdivided into natural and synthetic. These are further subdivided into monofilament and multifilament. Further classification is depending on the chemical composition, size and needle type.

Absorbable sutures decompose within the body. Natural absorbable sutures are digested by enzymes and synthetic absorbable sutures are hydrolyzed. Hydrolysis is gradual penetration by water leading to dissolution of polymer chains. It causes less tissue reaction. Absorption may be accelerated in those with fever, infection and protein deficiency.

Monofilament sutures are made of a single filament and multifilament sutures have multiple filaments either braided or twisted together. Twisted multifilament threads have considerable variability in their diameter and have a rough surface. Multifilament sutures have better knot holding security.

Monofilament sutures have a low tissue drag as it passes smoothly through the tissues resulting in lesser tissue trauma. Pseudo-monofilaments are braided sutures coated to improve tissue drag. Monofilament sutures are mainly used as thinner sutures as the wiriness of thicker sutures impair their handling and knotability. The tensile strength and knot tying ability depends on the material properties, structure and thickness.

Natural sutures are made from catgut, reconstituted collagen, cotton, linen or silk. Absorbable synthetic sutures are made from polylactic acid, polyglycolic acid or polydioxanone. The time at which absorbable sutures lose 50% of tensile strength is called half value and time at which it completely gets absorbed is called dissolution time. It varies depending on the material and its thickness.

Synthetic nonabsorbable sutures are made of polypropylene, polyester, polyethylene terephthalate, polybutylene terephthalate, polyamide, Goretex or stainless steel. They are colored to be seen better using dyes such as logwood extract, chromium-cobalt-aluminum oxide, ferric ammonium citrate pyrogallol, D&C Blue No. 9 & No. 6, D&C Green No. 5 & No. 6. They are often coated to reduce tissue drag. Coating materials used for absorbable sutures are poloxamer 188 and calcium stearate with a glycolide-lactide copolymer. Coating materials used for nonabsorbable sutures are wax, silicone, fluorocarbon, or polytetramethylene adipate.

Properties of Individual suture materials

Catgut

• Made from processed submucosa of sheep intestine
• Consists of highly purified collagen
• 2 types Plain & Chromic
• Rate of absorption determined by type of catgut, type of tissue, condition of tissue and general health of patient
• Plain catgut retains its tensile strength for 7-10 days and is completely absorbed by 70 days.
• Chromic catgut is treated with Chromium salt to delay absorption. It gets absorbed by 90 days. Retains tensile strength for 10-14 days. Causes less tissue reaction.

Poliglecaprone (Monocryl)

• Copolymer of glycolide and epsilon-caprolactone.
• Monofilament.
• Tensile strength is 60-70% at 7 days, 30-40% at 14 days and completely lost at 28 days for dyed monocryl.
• Tensile strength is 50-60% at 7 days, 20-30% at 14 days and completely lost at 21 days for undyed monocryl.
• Completely absorbed at 90-120 days.
• Mainly used for closure of subcutaneous tissue and for subcuticular sutures.

Polyglactin (Coated VICRYL)

• Copolymer of lactide and glycolide plus calcium stearate.
• Braided with coating.
• Tensile strength is 75% at 2 weeks, 50% at 3 weeks, 25% at 4 weeks and completely lost at 5 weeks.
• Completely absorbed by 56-70 days.

Polydioxanone (PDS)

• Composed of polyester poly p-dioxanone.
• Retains 70% tensile strength at 2 weeks, 50% at 4 weeks and 25% at 6 weeks.
• Minimally absorbed at 90 days. Completely absorbed at 6 months.

Surgical Silk

• Can be twisted or braided.
• Braided has better handling.
• Made from the cocoon of silkworm moth larva.
• Usually dyed black for easy visualization.
• Loses tensile strength when exposed to moisture, hence should be used dry.
• Although classified as nonabsorbable; loses its tensile strength at one year and is absorbed by two years.

Surgical Steel

• Monofilament or braided.
• High tensile strength, low tissue reaction and secure knot holding.
• 316 Alloy is used.
• Disadvantages
  • Difficult handling.
  • May tear or cut through tissues.
  • Fragmentation, barbing and kinking.
  • Breakage and stretching.
  • May puncture surgeon’s or patient’s skin.

Nylon

• Monofilament or braided.
• Categorized as nonabsorbable, but 15-20% removed each year by hydrolysis.
• Nylon grade 6 used for manufacture of sutures of size 7-0 and larger. Nylon grade 6-6 used for sizes 7-0 and smaller.
• Has poor knot holding capacity, hence more throws of knots are needed.
• Moistening improves handling.

Polypropylene (Prolene)

• Minimal tissue reaction.
• Can be used in contaminated and infected wounds.
• Needs multiple knots.
• Doesn’t lose strength or get absorbed.
• Used in tendon repair, nerve repair and vascular repair.

Needles

• Needle is an important component of sutures. Needles are made from stainless steel or carbon steel. They are nickel plated or electroplated. 420 steel, 455 steel and 300 steel are the commonly used steels. Of this 300 steel is of the highest quality, highest ductility and highest bending strength.
• Atraumatic needles are pressed or crimped into the suture materials to allow the diameter of the needle to be the same as the suture material.
• As per suggestion of the Technical Committee of the Association of Manufacturers of Surgical Sutures the needle are labeled as follows. The first letter denotes the needle shape, second the needle type, third and fourth letters if present denote special characteristics of the needle. The number that follows the letter denotes the length of needle in millimeters.

Recent developments

Surgical Glue

It uses chemical bond to hold the tissues together and to create a barrier for infection. Five main types of surgical glues used are the cyanoacrylates, fibrin based, collagen based, glutaraldehyde glues and hydrogels.

Surgical zipper

Staplers

Absorbable staplers