Suture Theory

Explore the depths of suturing wisdom, a realm where hands craft miracles. Be bold, be daring, and let the thread guide your hands towards mastery

Why do we suture wounds?

The main aims of closing a wound with sutures are to:

Accurately approximate skin edges. This is known as primary intention and produces a wound that is both functionally and cosmetically acceptable.
Prevent healing by secondary intention which may result in an unacceptable scar, both functionally and cosmetically.
Support the wound until its tensile strength recovers, helping prevent wound dehiscence.
Eliminate any dead space which could potentially harbour infection or bleeding leading to prolonged infections or a haematoma.
Reduce bleeding and or infection

Suture Classification

Absorbable vs Non-absorbable

Absorbable

Absorbable sutures such as Vicryl, Polydiaxonone (PDS), and Monocryl are gradually broken down by the body via enzymatic reactions (proteolytic enzymatic degradation) or hydrolysis, which is then absorbed by the body. As a result, absorbable sutures lose a significant amount of their tensile strength within 60 days of tissue insertion. These sutures are suitable for tissues that heal rapidly such as the stomach, bowel, bladder and subcutaneous tissues. They retain their tensile strength during the initial tissue mending process, and as tissues heal, the suture strength declines at a known rate for each specific material type. Absorbable sutures are also commonly used for subcuticular wound closure which can produce superior cosmetic results.

The complete absorption times for the more commonly used absorbable sutures are summarised below, although these times may vary due to factors such as ongoing infection, fever, or even protein deficiency.

Vicryl rapide - 42 days

Vicryl - 60 days

Monocryl - 100 days

PDS - 200 days

Non-absorbable

Non-absorbable sutures are synthesised from a variety of non-biodegradable materials such as nylon (Ethilon), prolene and silk Contrastingly, they maintain their tensile strength witin tissue for at least 60 days. These sutures are suitable for repair of tissues with slow healing times such as ligaments and tendons as they offer longer term tissue approximation. They are also used in blood vessel repair and vascular anastamoses with grafts, as well as fixation of hernia meshes.

Non-absorbable sutures can be utilised for skin closure, particularly where skin opposition is placed under tension or there is a risk of infection, For this, interrupted suturing technique is the technique of choice as removal of one or two stitches would not affect the wound healing process down or upstream. However, non-absorbable sutures for skin closure will require removal post-operatively, usually between three to fourteen days depending on the healing potential of the patient and the location of the wound (which is discussed below).

Synthetic vs Natural

Synthetic

These sutures consist of materials which are man made. As a result, their properties such as tensile strength and absorption can be calculated and predicted more accurately. This allows for wounds to be better managed, giving surgeons reassurance of the behaviour of the suture chosen in situ. These can be absorbable (Vicryl, Monocryl & PDS) and non-absorbable (nylon(Ethilon) & prolene).

Natural

Natural sutures are made of natural fibres derived from biological sources such as catgut or silk. Despite this, they are becoming less favoured as they can produce unwanted inflammatory reactions, comprimising wound healing. However, silk is still largely used for securing surgical drains. Natural sutures can be absorbable (catgut & collagen) or non-absorbable (silk, steel & cotton).

Monofilament vs Multifilament (Braided)

Monofilament

Monofilament sutures consist of a single strand. They manoeuvere smoothly through tissue with minimal tissue drag (friction) and harbour lower rates of infection due to the absence of pockets of spaces which bacteria favour. Some examples include: nylon (Ethilon), PDS and prolene.

However, monofilament sutures pose decreased knot security due to some of them having a tendency to maintain its original form, therefore, additional knots are required to reduce the propensity for the knot to unravel. Also, these suture types can be significantly weakened by any form of damage, either by kinks or by the surgical instruments. Monofilament sutures are largely preferred in vascular, tendon and nerve repairs

Multifilament (Braided)

These types of sutures are composed of several fibres twisted together into a single strand. Braided sutures are generally stronger and allow for better knot security but tend to produce more tissue drag. This is overcome with many manufacturers applying coatings to reduce tissue drag, however, also compromising knot security. Some examples include braided silk and Vicryl,

The intervening spaces that come as a result of these braids can be ideal for bacterial growth, and can lead to bacteria tracking into the wound, known as suture track sepsis. Infection can persist due to these bacteria being isolated from the immune system. Therefore, it is vital that multifilament sutures are not placed in contaminated areas. Multifilament sutures are particularly preferred in bowel surgery.

Suture Size

The size of a suture represents its diameter, which has a very close relationship with its tensile strength and handling properties. Historically, when sutures were thicker, size 1 was ascribed to the finest suture. As technology progressed sutures became thinner, therefore, this scale needed adjusting and was reversed.

Essentially, the sizing follows a scale similar to positive and negative numbers. A number to the right of o (or not preceded by a o) means the suture size gets progressviely larger. For example, a size 3 suture is larger than a size 2 suture, which is larger than a size 1. Conversely, a number to the left of o means that the suture size gets progressively smaller. For example, a 4-0 suture is smaller than a 3-0 suture, which is smaller than a 2-0. This is known as the United States/British Pharmacopeia Classification (USPC/BPC). This is further highlighted below with their respective uses within different tissue.

11-0 to 10-0: Used mainly for microvascular surgery

10-0 to 8-0: Used for delicate procedures such as ophthalmic surgery or nerve repairs

7-0 to 6-0: Used for facial plastics or small vascular repairs

5-0 to 4-0: Used for larger vascular repair or skin closures

3-0 to 2-0: Used tor muscle layers or wounds especially when there is high tissue tension

o to 1: Used for deep layers in the back, fascia layers in the abdomen (laparotomy closures) or joint capsules

2 to 5: Used for tendon repairs

When choosing the size of the suture, the surgeon will choose the smallest size required to adequately keep the wound closed in order to minimise trauma to the tissue. Bearing in mind that as sutures get smaller, tensile strength decreases too.

Removal Times

For non-absorbable sutures, the length of time that sutures are left in-situ is largely dependant on the site of the body where the wound is located.

Areas such as the face contain a superior blood supply, allowing for faster wound healing. Therfore, sutures placed here can be removed earlier, Alternatively, other anatomical sites such as the back have a poorer blood supply with tougher skin, slowing down wound healing. Hence sutures here will be required for longer before removal. The table below demosntrates the removal times based on different anatomical sites.

It is important to take into other factors that can significantly impact on wound healing. Patient factors include age, nutritional status and immunocomprimisation, Surgical factors include the gross surgical technique, choice of suture material and technique,