Sutures 06 How sutures work
Sutures 06 How sutures work
This subsection has text and images from an interactive multimedia training program on basic surgical skills called PrimeSkills in Surgery. You can use this subsection on its own or follow the whole program (further details at the end of this subsection).
How sutures work.
How sutures work
Sutures work in two ways.
First, the suture surrounds the tissue and compresses it to the required degree.
Second, the suture is knotted so that the pressure on the tissues will be maintained.
ie A suture should not break and the knot should not slip.
The surgeon uses the different properties of sutures described below to avoid these mishaps,
The length of the suture in the packets is designed to be:
Long enough to give a useful number of stitches per length.
Long enough to reach deep suture sites easily.
Short enough to prevent tangling.
Short enough to run through the tissues without cutting or bunching.
It would seem sensible to give a suture a gauge according to its diameter.
This is done with the metric system using tenths of a millimetre.
The metric sizes go down as the suture diameter decreases.
However, as the diameter of the stitches gets smaller, the difference between sizes also gets
Measuring the diameter in tenths of a millimetre becomes rather clumsy.
e.g. 4, 3.5, 3.2, 2, 1.5, 1, 0.7, and 0.4 tenths of a millimetre.
The older O (oh) gauge system remains popular because the downward steps in sizes are very convenient, and the numbering is
simple, although the numbers go up as the diameter decreases.
e.g. 1, 0, 2/0(called two-oh), 3/0, 4/0, 5/0, 6/0, and 7/0 for the metric sizes above.
"THREES AND TWOS PLUS/ MINUS A HALF"
3/0 is a metric 2, and a 2/0 is a metric 3.
This is a difference in diameter of one metric step (0.1mm.).
The other O sizes go up or down in half metric steps in this range of diameters.
NB. All catgut used to be a larger O gauge size than other types of suture, to allow for the weakness of catgut compared with the
suture materials used previously such as silk or linen.
To avoid confusion, get used to a small range of suture/needles.
Use the code numbers issued by the manufacturers for the suture/needle combination you want, rather than a description of the
Despite the efforts of the manufacturers, the sutures are folded or kinked to some degree in their packets.
This makes the sutures a bit springy and difficult to handle.
Pull on the suture to stretch the suture so that the kinking disappears or improves.
The force needed to straighten the suture is very close to the breaking strength of the swage.
Therefore, protect the swage from this pull by holding the suture instead of the needle.
An important aim in surgery is to know how much push and pull the tissues will stand from the stitches without being damaged.
However, you need to learn the strengths of the sutures before you start stitching the tissues, so that you choose sutures that are
The strength of a suture depends on:
The material (i.e. its molecular structure).
The diameter of the suture.
Whether it is braided or monofilament. (Braided is stronger)
The strength of any particular suture will be reduced by:
Any knots in it.
The swaging onto the needle.
Damage from dissecting forceps, needle holders, needles, and diathermy.
In surgery, the strengths of sutures and the amount of pull on sutures and tissues is usually given non-numerical terms such as:
Strong. Very strong. Gentle. Snug. Firm. Not too hard. Too much. Sister, this suture is rubbish! etc.
These are difficult to learn and are prone to wide variations between surgeons, leading to argument, frustration and blame.
Measuring the pull and strengths in absolute terms would seem to be sensible.
However, the official unit of strength used is a Newton.
This is unfamiliar to surgical staff, although it is almost exactly the same as a 10 gram weight.
Also the basic work on measuring the forces used by surgeons when stitching has not been done.
In this program, you will be learning to:
Estimate the amount of pull in grams.
Familiar weights: 1 litre of coke 1000gm./1 packet of butter 500gm./1 bar of soap 125gm.
Learn breaking strengths and ideal forces on tissues.
This is based on the measurements and experience of the author using a spring balance.
Research in progress should confirm whether other surgeons do about the same.
All suture strengths will apply to a suture with an overhand knot in it.
This is because a suture is weakened by a knot, and is only at risk of breaking when a knot is being tightened.
The strongest pull that a surgeon can give without getting severe pain in the hand is about 5000g.
Most sutures will feel slightly springy just before they break, but there is virtually no warning.
Needle Suture Length Knotted Swage Strength gm. Strength gm.
Ethicon 26mm. 3/8 curve 3/0 or 2 metric 150cm. 2000 1000 W9890 reverse cutting coated polyglactin (Vicryl) Ethicon 50mm. 1/2 curve 1 or 4 metric 100cm. 3800 4100 W749 round bodied polyamide(nylon) Ethicon 50mm. 1/2 curve 1 or 4 metric 75cm. 5000+ 2500 W9251 round bodied polyglactin(Vicryl) To straighten: 2500 Ethicon 30mm. 1/2 curve 2/0 or 3 metric 75cm. 3000 1400 W9136 round bodied polyglactin(Vicryl) To straighten: 1500 Ethicon 90mm. 3/8 curve 1 or 4 metric silk 50cm. 3900 5000+ W2793 cutting
Next subsection, click on Sutures 07 How to use sutures Last subsection, click on Sutures 05 Parts Surgical Education and Training page, click on Surgical Education and Training Whole program on WikiSurgery, click on PrimeSkills in Surgery Whole program on CD-ROM, click on Michael Edwards