Suture Overview

Sutures are the stitches that surgeons use to hold skin, internal organs, blood vessels and all other tissues of the human body together, after they have been severed by injury or surgery. They must be strong (so they do not break), non-toxic and hypoallergenic (to avoid adverse reactions in the body), and flexible (so they can be tied and knotted easily). In addition, they must lack the so called "wick effect", which means that sutures must not allow fluids to penetrate the body through them from outside, which could easily cause infections. Sutures have to comply with several regulations and guidelines such as United States Pharmacopeia and the FDA to ensure they meet the necessary requirements.

The United States Pharmacopeia (USP) was established in 1820 for standardization of suture materials and is the official public standards authority for other healthcare products designed, manufactured and sold in the United States. USP sets standards for the design and quality of medical products and works with healthcare providers to help them reach the standards. USP's standards are also used overseas in more than 120 countries. These standards have been helping to ensure good pharmaceutical care throughout the world for more than 185 years.



Suture Sizes

Suture sizes are defined by the United States Pharmacopeia. Sutures were originally manufactured ranging in size from #1 to #6, with #1 being the smallest. A #4 suture would be roughly the diameter of a tennis racquet string. The manufacturing techniques, derived at the beginning from the production of musical strings, did not allow thinner diameters. As the procedures improved, #0 was added to the suture diameters, and later, thinner and thinner threads were manufactured, which were identified as #00 (#2-0 or #2/0) to #000000 (#6-0 or #6/0).

Surgical Needles for use with Sutures

Traumatic needles are needles with holes or eyes which are supplied to the hospital separate from their suture thread. The suture must be threaded on site, as is done when sewing at home. Atraumatic needles with sutures comprised of an eyeless needle attached to a specific length of suture thread. The suture manufacturer swages the suture thread to the eyeless atraumatic needle at the factory. There are several advantages to having the needle pre-mounted on the suture. The doctor or the nurse does not have to spend time threading the suture on the needle. More importantly, the suture end of a swaged needle is smaller than the needle body. In traumatic needles with eyes, the thread comes out of the needle's hole on both sides. When passing through the tissues, this type of suture rips the tissue to a certain extent, thus the name traumatic. Nearly all modern sutures feature swaged atraumatic needles.

There are several shapes of surgical needles, including:

• straight
• half curved or ski
• 1/4 circle
• 3/8 circle
• 1/2 circle
• 5/8 circle
• compound curve

Needles may also be classified by their point geometry; examples include:

• taper (needle body is round and tapers smoothly to a point)
• cutting (needle body is triangular and has a sharpened cutting edge on the inside)
• reverse cutting (cutting edge on the outside)
• trocar point or tapercut (needle body is round and tapered, but ends in a small triangular cutting point)
• blunt points for sewing friable tissues
• side cutting or spatula points (flat on top and bottom with a cutting edge along the front to one side) for eye surgery

Absorbable and Non-Absorbable Sutures

Sutures are divided into two kinds - those which are absorbable and will break down harmlessly in the body over time without intervention, and those which are non-absorbable and must be manually removed if they are not left indefinitely. The type of suture used varies on the operation, with a major criteria being the demands of the location and environment:

Absorbable sutures are made of materials which are broken down in tissue after a given period of time, which depending on the material can be from ten days to eight weeks. They are used therefore in many of the internal tissues of the body. In most cases, three weeks is sufficient for the wound to close firmly. The suture is not needed any more, and the fact that it disappears is an advantage, as there is no foreign material left inside the body and no need for the patient to have the sutures removed.

Absorbable sutures were originally made of the intestines of sheep, the so called catgut. The manufacturing process was similar to that of natural musical strings for violins and guitar, and also of natural strings for tennis racquets. Today, gut sutures are made of specially prepared beef and sheep intestine, and may be untreated (plain gut), tanned with chromium salts to increase their persistence in the body (chromic gut), or heat-treated to give more rapid absorption (fast gut). In Europe and Japan, gut sutures have been banned due to concerns over bovine spongiform encephalopathy (mad-cow disease), although the herds from which the gut is harvested are certified BSE-free. Today, the majority of absorbable sutures are made of synthetic polymer fibers, such as polyglycolic acid (PGA), rapid polyglycolic acid (RPGA) or poliglecaprone 25, which may be braided or monofilament; these offer numerous advantages over gut sutures, notably ease of handling, low cost, low tissue reaction, consistent performance, and guaranteed non-toxicity.

Non-absorbable sutures are made of materials which are not metabolized by the body, and are used therefore either on skin wound closure, where the sutures can be removed after a few weeks, or in some inner tissues in which absorbable sutures are not adequate. This is the case, for example, in the heart and in blood vessels, whose rhythmic movement requires a suture which stays longer than three weeks, to give the wound enough time to close. Other organs, like the bladder, contain fluids which make absorbable sutures disappear in only a few days, too early for the wound to heal. Inflammation caused by the foreign protein in some absorbable sutures can amplify scarring, so if other types of suture are less antigenic (ie, do not provoke as much of an immune response) it would represent a way to reduce scarring.

There are several materials used for non-absorbable sutures. The most common is a natural fiber, silk, which undergoes a special manufacturing process to make it adequate for its use in surgery. Other non-absorbable sutures are made of artificial fibers, like polypropylene, polyester or nylon; these may or may not have coatings to enhance their performance characteristics.