An Introductory Guide to Suture Types

surgsoc

Knowing what's what with sutures doesn't have to be complicated. This bitesized guide by Harri Foster-Davies provides the information you need to know.

Harri Foster Davies

An Introductory Guide to Suture Types

Classification of a suture may depend on the needle or the suture thread. Below

is a diagram of suture packaging, demonstrating the variety of specifications:

Metric Gauge

Product Code

Imperial Gauge

Suture Thread Length

Expiry Date

Needle size and

curvature

Needle Point

Batch Number

Manufacturer

Needle

The ideal needle:

Sterile; high-quality stainless steel; stable in the grasp of

a needle holder; able to carry suture material through tissue

with minimal trauma; as slim as possible without compromising

strength; sharp enough to penetrate tissue with minimal

resistance; rigid enough to resist bending but not break.

1. Needle Size

The needle size describes the distance along the edge of the needle. This

typically varies anywhere from 4 mm right up to 90 mm. A smaller needle is more

suitable for delicate/thin/small tissues.

2. Needle Curvature


Harri Foster Davies

The needle curvature describes how tightly the needle curves. Common

measurements include:

• Straight – designed to be used by hand; mostly used for

skin closure or microsurgical procedures.

• Half-curved (ski) – used in laparoscopic surgery.

• 1/4 circle - a shallow curve and is used on easilyaccessible

convex surfaces, for instance, in ophthalmic

and microsurgical procedures.

• 3/8 circle – the most commonly needle curvature; easy to

manipulate in large/superficial wounds.

• 1/2 circle – suitable for confined locations.

• 5/8 circle – ideal for deep confined holes.

3. Needle Body and Points

Needles either have round bodies or triangular-shaped bodies.

• Round-bodied needles pierce and spread tissues with minimal cutting. They have

either sharp (taper-point) or blunt points.

o Taper-point - used in easily-penetrated tissues (e.g. abdominal viscera).

o Blunt - used to dissect through friable tissues (e.g. liver, kidney).

• Needles with triangular-shaped bodies are referred to as “cutting” needles.

They are used to penetrate tough tissues. They are either ‘conventional’ or

‘reverse’.

o “Conventional” cutting needles have the cutting edge on the inside arc of

the needle and are useful for skin and sternum.

o “Reverse” cutting needles have their cutting edge on the outside arc of

the needle and are ideal for tough tissue like skin, tendon sheath, or

oral mucosa. Reverse cutting needles have a reduced risk of tearing

through tissues compared to conventional cutting needles since tension is

not in the same vector as the cutting edge. These types of needles are

typically used in ophthalmic and cosmetic surgery, where minimal trauma is

paramount.

Suture Thread

The ideal suture:

Sterile; small as possible whilst providing high, uniform

tensile strength; consistent uniform diameter; appropriate

pliability; provides knot security; low bioreactivity.

The choice of suture material is based on the balance of certain

characteristics. Such characteristics can be grouped into 4 categories:

Physical, Handling, Biocompatibility, and Biodegradation.

• Physical characteristics include size (diameter), number of filaments,

tensile strength, elastic modulus, bending stiffness, stress relaxation, and

coefficient of friction.

• Handling characteristics include pliability, packaging memory, knot tiedown,

knot slippage, and tissue drag.

• Biocompatibility characteristics include inflammation, wound infection risk,

thrombus formation risk, carcinogenicity, and allergenicity.


Harri Foster Davies

• Biodegradation characteristics include absorbability, as well as the

biocompatibility of any breakdown products.

1. Suture Size

There are two classification systems: USP (United States Pharmacopeia) and the

European system. The USP grading is calculated using not only diameter, but

also tensile strength and knot security. The European system uses only the

diameter of the suture in millimetres.

As suture material is a foreign substance, it will cause inflammation. This

tissue reaction will continue until the suture material is absorbed or

encapsulated by fibroblasts. The smaller the suture diameter, the less the

tissue reaction due to decreased presence of foreign material. However, the

smaller the diameter, the weaker the tensile strength. As a general rule, the

smallest suture material that properly holds tissues should be used.

2. Suture Filaments

Suture strands can either be monofilament, braided, or twisted.

• Monofilament sutures are formed from one strand. They have a lower infection

risk and create less drag when passing through tissues. However, they have a

lower ease of handling and knot strength. They can also crimp easily,

resulting in weak spots that lessen tensile strength.

• Multi-filament sutures are comprised of several strands braided or twisted

together. They provide increased tensile strength and pliability but also

increase drag within tissues. Multi-filamentous sutures can be coated with

materials that lessen the drag and make knots easier to slide into place

(but this then results in poor knot security).

3. Suture Material

Suture material can be classified as absorbable or non-absorbable.

Types of absorbable suture include:

• Gut – a natural monofilament suture. Often used for internal soft tissue.

The body has a strong reaction to this suture material which often results

in encapsulation. Not commonly used outside gynaecological surgery.

• Polydioxanone (PDS) – a synthetic monofilament suture. Used for many types

of soft tissue wound repair (such as abdominal closures) as well as for

paediatric cardiac procedures.

• Poliglecaprone (Monocryl) – a synthetic monofilament suture. General use in

soft tissue repair. Most commonly used to discretely close skin.

• Polyglactin (Vicryl) – a synthetic braided multi-filament suture. Good for

repairing hand or facial wounds.

The absorbability of a suture is determined by the material it is made from and

the number of strands that comprise that suture. Natural suture will be

degraded by enzymes whilst synthetic suture will be degraded through hydrolysis

(i.e. water gradually penetrates the suture filaments, causing breakdown of the

suture’s polymer chain).

Types of non-absorbable suture include:

• Silk – a natural braided suture.


Harri Foster Davies

• Nylon (Ethilon) – a natural monofilament suture.

• Polypropylene (Prolene) – a synthetic monofilament suture.

• Cotton

• Stainless steel wires.

Non-absorbable sutures will retain their tensile strength for >60 days. They

are grouped into 3 classes: Class 1 (silk, nylon, and polypropylene); Class 2

(cotton and linen); Class 3 (metallic). Class 1 and 3 are the most popular as

class 2 is prone to infection and contamination. Non-absorbable sutures are

eventually encapsulated by fibroblasts.

Having read this brief guide, it may seem like there are thousands of potential

combinations of needles and sutures. However, it is important to remember that

most surgeons typically just find a few sutures that they prefer to work with

and stick with these (unless a particular procedure specifically asks for a

different suture/needle type). You will also find your preferences as you gain

experience!!

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