Introduction:

The goals of wound closure include obliteration of dead space, even distribution of tension along deep suture lines, maintenance of tensile strength across the wound until tissue tensile strength is adequate, and approximation and eversion of the epithelial portion of the closure. Methods for mechanical wound closure include staples, tape, adhesive, and sutures. Each method has specific indications, advantages and disadvantages. Suture closure permits primary wound healing. Tissues are held in proximity until enough healing occurs to withstand stress without mechanical support. Skillful wound closure requires not only knowledge of proper surgical techniques but also knowledge of the physical characteristics and properties of the suture and needle.

SUTURES:

Suture selection is dependent on the anatomic site, surgeon's preference, and the required suture characteristics. The main consideration in needle selection is to minimize trauma.

Suture qualities
Ideal suture characteristics
The ideal suture has the following characteristics:

• Sterile
• All purpose (composed of material that can be used in any surgical procedure)
• Causes minimal tissue injury or tissue reaction (ie, nonallergenic, noncarcinogenic)
• Easy to handle
• Holds securely when knotted (i.e., no fraying or cutting)
• High tensile strength
• Favorable absorption profile
• Resistant to infection

Unfortunately, at present, no single material can provide all of these characteristics.

The followingtermsdescribe various characteristics related to suture material:
Absorbable-Progressive loss of mass and/or volume of suture material; does not correlate with initial tensile strength
Nonabsorbable-Surgical suture material that is relatively unaffected by the biologic activities of the body tissues and is therefore permanent unless removed
Breaking strength-Limit of tensile strength at which suture failure occurs
Capillarity-Extent to which absorbed fluid is transferred along the suture
Elasticity-Measure of the ability of the material to regain its original form and length after deformation
Fluid absorption-Ability to take up fluid after immersion
Knot-pull tensile strength-Breaking strength of knotted suture material (10-40% weaker after deformation by knot placement)
Knot strength-Amount of force necessary to cause a knot to slip (related to the coefficient of static friction and plasticity of a given material)
Memory -Inherent capability of suture to return to or maintain its original gross shape (related to elasticity, plasticity, and diameter)
Plasticity-Measure of the ability to deform without breaking
Pliability-Ease of handling of suture material; ability to adjust knot tension and to secure knots
Tensile strength-Measure of the ability of a material or tissue to resist deformation and breakage
Wound breaking strength-Limit of tensile strength of a healing wound at which separation of the wound edges occurs
Straight-pull tensile strength-Linear breaking strength of suture material

Suture size
The United States Pharmacopeia (USP) classification system was established in 1937 for standardization and comparison of suture materials, corresponding to metric measures. The 3 classes of sutures are collagen, synthetic absorbable, and nonabsorbable.
Suture size refers to the diameter of the suture strand and is denoted as zeroes. The more zeroes characterizing a suture size, the smaller the resultant strand diameter (eg, 4-0 or 0000 is larger than 5-0 or 00000). The smaller the suture, the less the tensile strength of the strand.

Suture material and structure
Natural vs Synthetic sutures
Natural sutures can be made of collagen from mammal intestines or from synthetic collagen (polymers). Tissue reaction and suture antigenicity lead to inflammatory reactions, especially with natural materials.

Sutures

N.B. Tissue reaction and suture antigenicity may lead to inflammatory reactions with natural suture materials

Monofilament & multifilament sutures

N.B. The increased absorption of fluid may act as a tract for the introduction of pathogens, which increases the risk for wound infection and dehiscence with multifilament sutures.

Absorbable vs nonabsorbable sutures
Absorption occurs by enzymatic degradation in natural materials and by hydrolysis in synthetic materials. Hydrolysis causes less tissue reaction than enzymatic degradation.
Chemical treatments, such as chromic salts, lengthen the absorption time.
Accelerated absorption may occur in patients with fever, infection, or protein deficiency.

Suture characteristics

Absorbable sutures are used for:

1.Repairing rapidly healing tissues that require minimal support.
2. Ligating superficial blood vessels.
3. Conjunctival, subcutaneous tissue or mucosal closure
4. Muscles in strabismus and plastic surgery.

Nonabsorbable sutures elicit a tissue reaction that results in encapsulation of the suture material by fibroblasts. Used for:

1. Skin closure
2. Corneo-scleral suturing
3. Sling material for frontalis suspension
4. Musculocutaneous flaps

Many surgeons consider silk suture the standard of performance (superior handling characteristics). Although classified as a nonabsorbable material, silk suture becomes absorbed by proteolysis and is often undetectable in the wound site by 2 years. The problem with silk suture is the acute inflammatory reaction triggered by this material. Host reaction leads to encapsulation by fibrous connective tissue.
Surgical steel suture is made of stainless steel (iron-chromium-nickel-molybdenum alloy) as a monofilament and twisted multifilament. This suture can be made with flexibility, fine size, and the absence of toxic elements. Surgical steel demonstrates high tensile strength with little loss over time and low tissue reactivity.

Nonabsorbable synthetic sutures:
Nylon suture is a polyamide polymer suture material available in monofilament and braided forms. The elasticity of this material makes it useful in retention and skin closure. Nylon is quite pliable, especially when moist. The braided forms are coated with silicone. Nylon suture has good handling characteristics, although its memory tends to return the material to its original straight form. The material is stronger than silk and elicits minimal acute inflammatory reaction. Nylon is hydrolyzed slowly, but remaining suture material is stable at 2 years, due to gradual encapsulation by fibrous connective tissue.
Polyester suture material is formed from a polymer of polyethylene terephthalate. The multifilament braided suture maybe uncoated or coated with polybutilate (Ethibond) or silicone (Ti-cron). The coating reduces friction for ease of tissue passage and improved suture pliability. The suture elicits minimal tissue reaction and lasts indefinitely in the body. The material provides precise consistent suture tension and retains tensile strength.
Polypropylene (Prolene) is a monofilament suture that is a stereoisomer of a linear propylene polymer. The material does not adhere to tissues and is useful as a pull-out suture (eg, subcuticular closure). Polypropylene also holds knots better than other monofilament synthetic materials. This material is biologically inert and elicits minimal tissue reaction. This material is useful in contaminated and infected wounds.
Surgipro II is a polypropylene suture that has been developed with increased resistance to fraying, especially with smaller diameter sutures. This suture is extremely inert in tissue and has been found to retain tensile strength in tissues for as long as 2 years. Surgipro II is widely used in plastic, cardiovascular, general, and orthopedic surgery.

Suture selection
A wide variety of suture materials are available for each surgical location and requirement. Generally, the surgeon selects the smallest suture that adequately holds the healing wound edges. As the wound heals, the relative loss of suture strength over time should be slower than the gain of tissue tensile strength. Therefore, consider nonabsorbable suture in skin, eyelid margin and sclera (slowly healing tissues), whereas conjunctival and mucosal wounds (rapidly healing tissues) may be closed with absorbable sutures.

Aesthetic concerns
Aesthetic concerns are at a premium in the anatomic regions of the head and neck, such as the eyelid, periorbital area, nose, pinna, lip, and vermillion. In these areas, tensile strength requirements tend to be less, and smaller suture sizes are preferred.

Contaminated tissues
Multifilament sutures are more likely to harbor contaminants than monofilament sutures. Because the presence of foreign bodies in contaminated tissues may facilitate infection, special consideration to be given to suture selection in a contaminated posttraumatic wound. Use the smallest inert monofilament suture materials, such as nylon or polypropylene, in this setting.

Suture size
Optimal suture size is generally the smallest size necessary to achieve the desired tension-free closure. If wound tension is high, smaller-diameter sutures may actually injure tissues by cutting through them. Therefore, closely match the tensile strength of the suture and tissue.

NEEDLES:

The earliest needles in history were made from animal bones or metals such as silver, copper, aluminium and bronze wires. Eyed needles are reusable as any thread and needle combination is possible to suit the job at hand. Swaged or atraumatic needles comprise a pre-packed needle attached to a specific length of suture thread. The chief advantage of this is that the doctor or the nurse does not have to spend time threading the suture on the needle, which may be difficult for very fine needles and sutures.

Characteristics of ideal needle
The ideal needles should have the following properties:
a. Enough rigidity to prevent easy bending
b. Sufficient length so that it can be grasped by the needle holder during passage and retrieval without causing damage to the tissue
c. Sufficient diameter to create a tract for the suture knot to be buried
d. As atraumatic as possible

The length, diameter, and curvature of the needle influence the surgeon's ability to place a suture. Wound closure and healing is affected by the initial tissue injury caused by needle penetration and subsequent suture passage. Needle selection, surface characteristics of the suture (eg, coefficient of friction), and suture-coating materials selected for wound closure are important factors that must be considered by the surgeon.

Parts of the needle
Nowadays needles are made of surgical stainless steel alloys which have excellent resistance to corrosion. The needle may be coated with silicone. The coating helps to reduce the force needed to make initial tissue penetration and the frictional forces as the body of the needle passes through the tissue.
There are three parts in a needle:
1. Swage (connection point for the suture)
2. Body
3. Point

Dimensions
1. Length - distance of the circumference from the swage to the point
2. Chord length - distance of the straight line from the swage to the point (which determines the width of the bite)
3. Radius- length of the line from the center of the circle
4. Needle diameter - measured in mils (1/1000 of an inch)
1 mil is about 25 um. A smaller diameter needle required less force and cause less trauma during passage through the tissue
5. Bicurve - two radii on a needle, the radius near the point is usually shorter than the radius of the body near the swage.

Types of needle
Types are classified based on the shape and curve as;

(1) Straight
(2) Compound curve
(3) Half curved (also known as ski)
(4) Half curved at both ends of a straight segment (also known as canoe)
(5) 1/4 Circle
(6) 3/8 Circle
(7) 1/2 Circle.
(8) 5/8 Circle

Clinical applications

3/8 circle needle is commonly used in ocular surgeries.
The sharp curve of the ½ circle needle is ideal for orbital tissues.
Examples: lateral tarsal strip to attach the lateral canthal tendon to the periosteum.
Inferior fornix formation.
Mucosal flap closure in dacryocystorhinostomy.

Point types
(1) Cutting
(2) Reverse cutting
(3) Taper
(4) Spatula

The following terms describe various characteristics related to needle performance:

Strength -Resistance to deformation during repeated passes through tissue (ie, increased needle strength results in decreased tissue trauma)

Ductility -Resistance (of a needle) to breakage under a given amount of deformation/bending

Sharpness -Measure of the ability of the needle to penetrate tissue; factors affecting sharpness include the angle of the point and the taper ratio (ie, ratio of taper length to needle diameter)

Clamping moment -Stability of a needle in a needle holder, determined by measuring the interaction of the needle body with the jaws of the needle holder

Needle selection
No standardized sizing system or nomenclature is available for needles or needle holders. The main consideration in needle selection is to minimize trauma. A taper needle is sufficient for tissues that are easy to penetrate. Cutting needles are typically reserved for tough tissues. As a general guide, select tapered sutures for all closures except skin sutures. The length, diameter, and curvature of the needle influence the surgeon's ability to place a suture. The needle-body diameter ideally matches the suture size.

Needle-holder selection
As discussed earlier, needle control and performance is affected by the stability of the needle within the needle holder; thus, for a secure needle hold and prevention of rocking, turning, and twisting, the jaws of the needle holder must be appropriate to the needle size. Often, the surface contact with the needle-holder jaws and the bending moment of the needle is maximized with an ovoid cross-section of the needle body.
In addition, the handle of the needle handle must be appropriate for the depth needed for the suture placement. A mechanical advantage for exerting force through the needle point is created by the difference between the length of the handle and the jaw.
The needle-holder clamping moment is a measure of the force applied to a suture needle by the needle holder, and the needle-yield moment is the amount of deformation that can occur before a needle is permanently deformed. Thus, when the needle-holder clamping moment is greater than the needle-yield moment, the needle is likely to be permanently deformed, which may lead to complications.
The stability of the needle within the needle holder affects needle control and performance. The jaws of the needle holder must be appropriate to the needle size to hold it securely and prevent rocking, turning, and twisting. The size of the needle should correspond to the size of suture. The choice of the needle depends on the the strength required to keep the tissues sewn together.

Suggested Reading

1. www. mrcoph.com.sutures/needles
2. Jeffrey A. Nerad. Oculoplastic surgery. The requisites in Ophthalmology.
3. Steven et al. Sutures and needles. Emedicine. medscape. 2013.