Definition

SUTURE

• Surgical suture (commonly called stitches) is a medical device used to hold body tissues together after an injury or surgery. Application generally involves using a needle with an attached length of thread. Sutures are used to repair tissue and facilitate healing
• Single-armed suture: the classic combination consists of a thread and a single needle.
• A double-armed suture consists of a thread with a needle at each end.

LIGATURE

• A strand of material used to identify or differentiate anatomical structures and to clamp blood vessels or ducts.

Characteristics of threads used for sutures

Thread memory is the capacity of the suture thread to return to its former, packaged shape. Thread memory has little effect on the quality of the suture, however it does affect manageability, as threads with memory tend to form knots spontaneously during use.

Tensile strength is defined as the force required to break a suture. The knot tensile strength is usually 30 to 50% less than the linear tensile strength of a suture. The suture material and diameter are key factors where tensile strength is concerned.

The capillarity of a suture describes the ease with which fluids can be wicked along the suture thread. This property is inherent to multifilament sutures as a result of the loose interstices of their fibers.

Surgical suture material can be classified on the basis of the characteristics, absorbability, origin of material and thread structure.

Absorbability

Absorption = resorption = loss of mass.

The rate of absorption of absorbable sutures depends on what they are made of and their thickness. Disappearance of the suture occurs through inflammatory reaction, hydrolysis or enzymatic degradation.

Absorbable sutures may be used to hold wound edges in approximation temporarily, until they have healed sufficiently to withstand normal stress. Some are absorbed rapidly, while others are treated or chemically structured to lengthen absorption time.

Non-absorbable sutures are those which are not digested by body enzymes or hydrolyzed in body tissue. They are made from a variety of non-biodegradable materials and are ultimately encapsulated or walled off by the body’s fibroblasts. When used for skin closure, they must be removed postoperatively.

Origin of material :

• Natural absorbable sutures: CATGUT: thread of animal origin.
• Natural non-absorbable sutures
• Silk fibers, often coated with wax or silicone. Tensile strength decreases as moisture is absorbed and is completely lost within 1 year.
• Cotton or linen fibers, or coated natural fibers where the coating contributes to suture thickness without adding strength.
• Metal wire of monofilament or multifilament construction.
• Synthetic origin: produced from synthetic polymers as polyamide, polyolefines and polyesters.

Number of strands:

Sutures are classified according to the number of strands of which they are comprised

Synthetic absorbable sutures

Absorbable sutures are medical devices class III according to rule 8 (surgically invasive long term use, mainly absorbed)

characteristics

Low tissue reaction.

Absorption occurs by enzymatic process. This process can become altered in patients with a fever, infection or protein deficiency, resulting in an accelerated decline of tensile strength. Furthermore, the absorption process can begin prematurely if the sutures are placed in a moist or fluid filled part of the body, or if the material becomes wet or moist during handling or any other time prior to implantation.

composition

Most of synthetic absorbable sutures are made of absorbable polyesters and contain one or more of the five basic building blocks: Glycolide, L-lactide, p-dioxanone, ε-caprolactone and trimethylene carbonate

Table 1: Synthetic absorbable sutures

PGA and PGLA sutures rapid

Absorption rate is higher for the sutures “Rapid” “Fast” or “Quick”: treating absorbable braided sutures with gamma radiation reduces their resistance. Tensile strength 50% @ 5 days, absorption complete by 42 days (PGA rapid is sometimes indicated as PGAP).

Synthetic non-absorbable sutures

Low tissue reaction, uniform and resistant.

Non absorbable sutures are in general medical devices class IIb according to rule 8 (surgically invasive, long term use)

If the suture is intended to be used in direct contact with the heart or central circulatory or nervous system, the medical device class becomes III)

Table 2: Synthetic non-absorbable sutures

Gauge of suture threads

Two parallel systems are used for measuring the gauge of thread (size of the thread):

• EP (European Pharmacopoeia) measurement: decimal size, representing a tenth of the thread diameter, expressed as a Metric size number (Metric 2 = DEC2 = 0.20 mm diameter). It ranges from 0.1 to 7.
• USP (United States Pharmacopoeia) measurement: ranges from 11/0 to 5 (the more zeros in the number, the finer the thread)

Length of the sutures: there is no standard length for the sutures. Manufacturers offer different lengths for each suture, habits change per country, very thin threads are often shorter.

Other features

Colour

The suture threads are available dyed (violet, green, blue, black, etc.) or undyed. The colour acts as an indicator, which can be particularly useful in certain cases (e.g. vascular surgery) for distinguishing the different anatomical structures. The colour enhances their visibility, even if they are steeped in blood. In contrast, undyed threads have the advantage of being less visible and more discreet, and thus better for use in eye surgery or skin suturing, to avoid a tattoo effect.

Coating

Coating is a surface treatment that can be used for the needle as well as for braided sutures and has the purpose of modifying the surface.

Coating the needles improves precision and penetration. Coating the thread optimizes its passage through the tissue and at the same time makes it less traumatic while still maintaining good knot security. However, this surface coating is thin and friction during manipulation can rub off the protective coating.

Antimicrobial suture

They contain / are coated with an agent to locally inhibit bacterial growth: triclosan or chlorhexidine.

• prevent bacterial adhesion and biofilms formation and avoid long-term systemic antibiotics.
• be biocompatible with medical products
• do not impair healing processes and be well tolerated in wounds with no toxicity or systemic absorption.

Barbed suture

The knotless barbed suture is widely used in both skin and deeper structures. It is a specifically designed monofilament suture (absorbable or non absorbable) with barbs orientated in the opposite direction to the needle. While suturing tissue, these barbs penetrate inside the tissue and lock them into place, eliminating the need for knots to tie the suture. Initial fixation of the suture is with a fixation tab or a loop.

Three types according to the direction of the barbs: bidirectional, unidirectional or spiral

PTFE Pledgets

Reinforcement of a suture: PTFE pledgets are used as a suture buttress

• Protect tissue from thread tension
• Distribute tension evenly across the pledget
• Enable better tightening

Various materials and sizes available, packed separately or preloaded on the suture

Control release needle

To save time, the needle-thread combination has been constructed with a removable needle. After the suture has been placed, the needle can be removed from the suture with a slight pull.

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The suture needle

In addition to the thread, the needle is an essential component of sutures.

Atraumatic sutures are defined as needle-suture combinations, where the (eyeless) needle is firmly attached (swaged) to the suture in order to reduce tissue trauma.

General characteristics

Most of surgical needles are fabricated from heat treated steel. There is no formal definition on what constitutes a "surgical stainless steel", so product manufacturers and distributors apply the term to refer to any grade of corrosion resistant steel.

The most common "surgical steels" are austenitic 316 stainless and martensitic 440 and 420 stainless steels.

The surgical needle has a basic design composed of three parts

• The point is the sharpest portion and is used to penetrate the tissue. The point runs from the tip to the maximum cross-sectional area of the body.
• The body represents the mid portion of the needle, made of solid steel. It is the strongest and widest portion of the needle and is also referred to as the grasping area.
• The swage is the portion to which the suture material is attached. Instrumentation here will break or weaken the suture. This part permits the suture and needle to act as a single unit to decrease trauma

Shape of the needle

Needle Body

Needles with round bodies pierce and spread the tissues with minimal cutting. They are used in easily penetrated tissues like the peritoneum and abdominal viscera.

Needles with triangular shaped bodies are referred to as “cutting” needles. Each of the three edges is a cutting edge, and they are used to penetrate tough tissues and are ideal for suturing skin.

Needle curvature (longitudinal shape)

In practice, the deeper the layer, the more curved the needle should be.

• 1/4 circle: shallow curvature, used on easily accessible convex surfaces: for ophthalmic and microsurgical procedures
• 3/8 circle: most commonly used needle. The curvature makes it easy to manipulate in large and superficial wounds, however it is impossible to use in deep cavities due to the large arc of manipulation needed.
• 4/8 = ½ circle: to be used in confined locations, but requires more pronation and supination of wrists
• 5/8 circle: ideal for deep, confined holes (nasal cavity), and can be used by rotating the wrist with little to no lateral movement.

Needle Point

• Taper point: needle body is round and tapers smoothly to a point. Penetrates the tissue by separating rather than by cutting.
• Conventional cutting: has a triangular cross section with the apex of the triangle on the inside of the needle curvature. The effective cutting edges are restricted to the front section of the needle and merge into a triangulated body which continues for half the length of the needle.
• Reverse cutting needle: is triangular in cross section, having the apex cutting edge on the outside of the needle curvature. This improves the strength of the needle and particularly increases its resistance to bending.
• Protection point: designed to minimize the risk of needle stick injury. The needle point is sharp enough to penetrate fascia and muscle but not skin.
• Blunt point: designed to suture extremely friable tissue such as liver.
• Tapercut needle: combines the initial penetration of a cutting point with the minimized trauma of a round bodied needle. The cutting is limited to the point of the needle, which then tapers out to merge into a round cross section.
• Side cutting or spatula points: flat on top and bottom with a cutting edge along the front to one side, for eye surgery

Sutures selected by MSF

The list of sutures has been drawn up by a group of surgeons who wished limiting their number while keeping a sufficient range to cover the surgical needs in the MSF missions.

Norms

The sutures must meet the characteristics and tests described in the pharmacopoeia. They must also meet the essential requirements of medical devices.

Characteristics

• Material: the selected sutures are all synthetic. The use of catgut is forbidden within MSF because it has unstable characteristics and involves a risk of contamination (bovine spongiform encephalopathy, scrapie...)
• Absorbable sutures braided (SSUTSABB+++) and the absorbable sutures braided rapid (SSUTSABR+++): coated polyyglycolid (PGA) or polygalactin 910 (PGLA), both materials are considered equivalent.
• Absorbable sutures monofilament (SSUTSAMD+++): polydioxanone = different type of material that has different characteristics.
• Non absorbable sutures, monofilament (SSUTSNAM+++): nylon (PA) and polypropylene (PP) are considered equivalent for most applications, unless specified otherwise.
• Length: sutures are 70 to 75 cm long (ligatures = 250 cm), variations occur according to the manufacturer.
• Surface: the absorbable braided sutures are coated, the monofilament sutures are not. All sutures have a smooth surface without barbs or pledgets and without antibacterial coating.
• Colour of the suture: the absorbable sutures are most often violet, the rapid ones are undyed. The specification coloured or undyed will only be added when necessary (important for plastic surgery, for intradermal continuous suture)

Codes and labels

The MSF labels are generic and mention the main characteristics of the selected sutures

• absorbable or non absorbable
• braided or monofilament
• gauge in USP measurement
• type of needle (curvature, length, type of point)
• double needle in case the suture is double armed
• all sutures are sterile and for single use, this is not specified in the label because lack of space

The codes of the sutures

• Family: SSUT
• Root: identifies the material
• SSUTSABB = absorbable braided
• SSUTSABR = absorbable braided rapid
• SSUTSAMD = absorbable monofilament PDA
• SSUTSNAM = non absorbable monofilament
• Qualifier:
• The gauge of the thread: 1 for gauge 1, 20 for gauge 2/0, 30 for gauge 3/0…
• The next letter identifies the tip of the needle
• T (trocar)
• R (reverse cutting
• C (conventional cutting
• B (blunt / protection point)
• The following digit is a sequential numbering for all other specifications (mainly linked to the needle: length, curve..)

Table 1: Synthetic absorbable sutures

Table 2: Synthetic non-absorbable sutures

*in common usage, the prefix 'PA' (polyamide) or the name 'Nylon' are used interchangeably and are equivalent in meaning

d'usage courant, le préfixe «PA» (polyamide) ou le nom «Nylon» sont interchangeables et ont un sens équivalent