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Suture materials and patterns  

Objectives:  To familiarize the veterinary technician with the principles of suturing, the materials used, and the common patterns used in suturing skin incisions.

Keywords:  absorption, monofilament, braided, twisted, sheathed, chromic gut, tensile strength, cutting, reverse cutting, taper, swaged, simple interrupted suture patter, horizontal mattress suture pattern, vertical mattress suture pattern, continuous suture pattern, stints, tension sutures, subcuticular sutures 


Reading Assignment:  Clinical Textbook for Veterinary Technicians by McCurnin and Bassert, 6th edition,  pgs. 1001-1007

Website demonstrating various suture techniques from the University of Pennsylvania
http://cal.vet.upenn.edu/projects/surgery/index.htm
If a window requesting a password comes up with this website, just hit cancel, and it should allow you access.

Recently the Board of Veterinary Medicine of Virginia revised the practice act to allow Licensed Veterinary Technicians to suture skin incisions and wounds. Technicians are now expected to become competent in this skill. Certainly not every veterinarian will expect technicians to suture, but it is a valuable skill.  Be sure to check with the state you practice in, as regulations for each state varies.

I) Suture materials:

Wounds have been "sutured" for at least 2500 years. In ancient times lacerations were pulled together with hair, leather and small bones. Gut suture (using the intestines of animals) has been used for about 2000 years, and remains popular today. Galen is credited with the first reference to catgut in 175 AD. Natural fibers such as leather, flax, and cotton were improved until synthetic sutures emerged from polymer technology.

The perfect suture has not yet been developed. The ideal suture should be:
A) Strong
B) Non-reactive in tissue
C) Non-slipping (hold knots)
D) Easy to handle
E) Inexpensive.

II) Suture materials have been classified in various ways including:

Absorption

Construction

Composition

1) non-absorbable
(remains strong 60 days+)

1) monofilament

1) natural materials

2) absorbable
(body will dissolve in <60 days

2) braided
3) twisted
4) sheathed

2) synthetics

III) Common sutures used in veterinary medicine

A) Natural products: includes rarely used products like cotton, linen, and kangaroo tendon, as well as the following:
   1) Silk: Silk is produced by silkworms and is non-absorbable
       a) A very flexible (limp) suture and has no "memory," considered the easiest to handle of all.
       b) Used often in neurology and ophthalmology
   2) Chromic gut: Gut made from the intestines of sheep and cattle. It is usually treated with chromic acid to decrease itsí tissue reactivity. Gut comes in various grades depending on the amount of treatment with chromic acid. General information regarding gut sutures:
       a) It is very reactive will often cause inflammation at site of use
       b) It has a wide range of absorption times (3-40 days) depending upon the amount of treatment with chromic acid.
       c) Gut suture is not used to close the skin
       d) It is inexpensive compared to other suture.
       e) It swells and extra knots are required to prevent slipping of the knot

B) Metal: Stainless steel (an alloy) is sometimes used in skin to prevent the patient from chewing out the suture line
   1) It is non-reactive
   2) It is difficult to handle and can cause perforations in gloves

C) Some synthetics: Very popular for both skin and deep sutures

trade name

material/source

absorption rate

        use

1) Vetafil / Braunamid

nylon

non-absorbable

skin primarily

2) PDS II

polydioxanone

slow absorption

wide range/skin/eye etc

3) Dexon

polyglyolic acid

absorbable

wide range

4) Vicryl

polyglactin

slow absorption

urinary, intestines

5) Prolene

polypropylene

non-absorbable

within body cavity

 D) Braided versus monofilament suture: Braided suture may be a nidus of infection, i.e. bacteria may lodge within the braid and become the source of an infection.

   E) Sizing and strength of suture materials:
       1) 6-0 is "hair-like" used for delicate surgery, i.e. ophthalmology and vascular

       2) 2-0 & 3-0 is the most commonly used in small animals

       3) 2-0 has an approximate tensile strength of 4 lbs.

       4) 1 has an approximate tensile strength of 7.5 lbs.

Relative size of different sutures

   E) Packaging of suture:
       1) Most veterinarians now use individually wrapped packages of sterile suture, often with a needle already attached (swaged on).
       2) Suture is also supplied on a roll inside a container of sterile preservative. Individual lengths of suture can be cut as needed as needed from the roll.

       3) Suture is also supplied on large bulk rolls (non-sterile) various lengths can be cut, packaged and sterilized.

Why are many brands of synthetic sutures bright colors?

II) Suture Needles: There are over 100 shapes of needles used on different organs or for various procedures. Needles are made of stainless steel and are strong but somewhat flexible and will bend before breaking.
Needles are classified by:
   A) Shape of needle:
        1) Straight
        2) Ski or semi-curved, the curve is only at the pointed end of the needle
        3) Curved: The curve can range from ľ to 5/8 circle, the more curved a needle the deeper penetration.

   B) Tip: The tip determines how the needle will penetrate tissue. Cutting edge needles have three sharp surfaces which, can penetrate and drive through tough tissue (if sharp).  Taper needles have rounded bodies and the tip can range from sharp to fairly blunt.
The three main types of needle tips are:
       1) Cutting:  Cutting edge is TOWARDS the skin margin

       2) Reverse cutting:  cutting edge is AWAY from skin margin

       3) Taper: Somewhat blunt tip used on easily penetrated tissue.


Why are reverse cutting edge needles often preferred in areas under pressure (heavy weight)

hint: Compare the "footprint" of a cutting and reverse cutting needle used to close a incision, look at the base of each footprint closely, which one do you think will have a tendency to cut or pull through tissue?

   C) The needle body shape (in cross section): Shapes range from rectangular to round.

   D) Eye: The part of the needle holding the suture
       1) Regular or standard, a closed eye, sometimes the suture material is double threaded through the eye so that is doesnít lip.
       2) Spring eye (sometimes termed a French eye): it allows suture to be pulled out with pressure
       3) Swaged: The suture is embedded inside the shaft of the needle and creates less drag and tissue trauma and doesnít slip out of the needle.
   E) Sizing of needles: The larger the number the smaller the needle, i.e. #20 needle smaller than #2. (similar to hypodermic needles)

III) Suture patterns: There are numerous patterns developed over the years each for a specific use. Veterinarians develop preferences for certain suture patterns, just as they do particular instruments, types of suture and needles. Some of the basic patterns used frequently in veterinary medicine include:

   A) Simple interrupted: This is a "safe" pattern. There is less chance of the suture line breaking since individual stitches are placed. It takes more time to place this pattern since there is an individual knot for each stitch. But if one suture is broken the rest of the line usually holds.

   Variations on the interrupted pattern include "tension sutures," which are placed away from the wound edge and hold more weight than regular sutures.

      1) Horizontal mattress

      2) Vertical mattress                                  
   

      3) Cross mattress

      4) Tension suture with tubing

 

   B) Continuous or running pattern: This suture pattern is fast but less secure since there is just one suture used and it is tied or knotted at each end of the closure, if either knot loosens or the suture breaks the entire line is lost.

 

    C) The "hidden" sub-cuticular pattern: This is usually a continuous pattern but an interrupted pattern could be used. It is placed in the dermal and sub-cutaneous layer of skin and is often used in canine castrations or as a strengthening layer below skin sutures.

IV) Knots: Without secure knots the best suture pattern would be useless. Many surgeons put extra ties or "throws" on their knots, this only takes a second and often insures that the knot will not slip. Common knots used in veterinary practice include:
   A) Square knot: Most commonly used knot.
   B) Surgeonís knot : A double loop is placed before the first throw of the traditional square knot is made.
   C) Granny knot: This is actually an incorrectly tied square knot. It looks very similar to the square knot, but doesnít hold as well.

Please enjoy this website on sutures:

http://www.vetmed.auburn.edu/~hendera/guide/guide1.htm#outlinetp://www.vetmed.auburn.edu/~hendera/guide/guide1.htm#outlineche  

V) Surgical staples: Staples are made of stainless steel and are applied using staplers. They have been used for surgical purposes for over 100 years and were invented in Russia. Below are some is some basic information regarding surgical staples.
   A) They are uniform, non-reactive, and time saving
   B) They are expensive (around a $1.00 each)
   C) An extractor needed for removal of staples from the skin
   D) They are used most often for long incisions, i.e. equine, orthopedics

VI) Ligating clips: These can be used in place of internal sutures to "tie off" pedicles (ovarian) or vessels etc. Ligating clips are applied by a special instrument and are stainless steal. They are used internally. They have similar qualities and drawbacks as staples.

VII) Surgical glue or tissue adhesives: This method of "pulling skin together" has become very popular. Below is some basic information about surgical glue and itís use.
   A) It is used commonly for feline declaws and to close small wounds.
   B) The product warning emphasizes not to place adhesive in or on blood because it will not be effective.
   C) It dries within seconds and is considered cost effective
   D) A trade name product is Nexaband, which was developed for the veterinary market.

VII) Biological coagulants: These products promote the formation of blood clots and resulting hemostasis. Most come as sterile powders or as sponges. They are used to stop capillary bleeding within body, i.e. liver seepage, tooth removal.
Examples include Gelfoam and Surgicel, which are gelatin and cellulose based products

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Suturing Assignment:  The on campus laboratory exercise will include suture practice on inanimate objects. Please practice the interrupted and continuous suture patterns before coming to campus.  Many materials will simulate skin edges - felt, leather, and rubber tubing can be sutured.  Additionally, you can use oranges, bananas, and tomatoes to simulate skin.  To practice tying square knots, get a piece of clothesline-type rope. Practice tying knots, practice your hand ties, and instrument ties with this rope as well.
Your mentor will instruct you as to techniques preferred in your practice, but here are a few things to remember:

1) Skin edges should be evenly opposed, with no inversion or puckers.

2) If stitches are placed too far from the incision site, there will be a "gap" or pucker,

3) If they are placed too close to the edge they are difficult to remove and may pull through the skin.

4) Most suture will cause some inflammation (especially surgical gut) if the suture is placed "tight" a day or two later there will be swelling and discomfort at the site. This can result in the suture line breaking or being chewed out by the patient.

5) Most veterinarians prefer a slightly loose suture to avoid the previous problem.


Questions: Answers to be e-mailed to Dr. Bidwell: abidwell@nvcc.edu

Don't forget to do the questions posed throughout this lecture in addition to the following questions!

1) What types of needles and sutures are used in your practice? What types of suture patterns do the veterinarians use for various surgeries?

2) What is suture memory?

3) What is a drawback in the use of polyester suture (ethicon etc.)?

4) How long should the "tails" be on skin sutures?

5) Would you prefer to use 6-0 or 3 size suture on the abdomen of a horse?

6) Why are reverse cutting edge needles preferred if a non leaking incision line is required?

7) What is the disadvantage of double threading a needle?

8) Which needle is the most atraumatic and most popular?

9) Does your practice use any alternative suturing methods, surgical glue, staples, ligating clips? In what ways?

The science and art of surgery has advanced well beyond the use of raw natural products closure.