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Sutures

The ideal suture would be totally biologically inert and cause no tissue reaction. It would be very strong but simply dissolve in body fluids and lose strength at the same rate that the tissue gains strength. It would be easy for the surgeon to handle and knot reliably. It would neither cause nor promote complications. Whilst there have been very great improvements in suture materials in the recent past and modern sutures are very close to above ideal, no single suture is ideal in all circumstances.

Different tissues have differing requirements for suture support, some needing only a few days eg muscle, subcutaneous tissue, skin; whilst others require weeks or even months eg fascia and tendon. Vascular prostheses require longer term, even permanent support. The surgeon must be aware of the differences in the healing rates of various tissues when choosing a suture material. Individual patient variation further complicates the decision. Healing of wounds is delayed by a range of factors such as infection, debility, respiratory problems, obesity, collagen disorders, malnutrition, malignancy, drugs eg cytotoxics and steroids. The surgeon wants to ensure that a suture will retain its strength until the tissue regains enough strength to prevent separation. Some tissues heal slowly and may never regain preoperative strength. Some may be placed under natural tension such as a tendon repair so the surgeon will want suture material that retains strength for a long time. In rapidly healing tissue, the surgeon may use a suture that will lose its tensile strength at about the same rate as the tissue gains strength and that will be absorbed by the tissue so that no foreign material remains in the wound. With all sutures, acceptable surgical practice must be followed with respect to drainage and closure of infected wounds. Excess tissue reaction to the suture encourages infection and slows healing. When taking all these factors into account, the surgeon has several choices of suture material available. Subjective preferences such as familiarity with the material and availability need also to be taken into account.

Absorbable and Non-absorbable

Sutures can conveniently be divided into two broad groups : absorbable and non absorbable. Regardless of its composition, suture material is a foreign body to human tissue and will elicit a foreign body reaction to a greater or lesser degree. Two major mechanisms of absorption result in the degradation of absorbable sutures. Sutures of biological origin such as surgical gut are gradually digested by tissue enzymes. Sutures manufactured from synthetic polymers are principally broken down by hydrolysis in tissue fluids and are preferred. Non absorbable sutures, made from a variety of non biodegradable materials, are ultimately encapsulated or walled off by fibroblasts.

Non absorbable sutures ordinarily remain where they are buried within the tissues. Improvements in absorbable sutures mean that they can be used in a variety of situations where previously surgeons would have recommended non-absorbable materials. It could be said that it is always best to use an absorbable suture unless there is a good reason not to. When used for skin closure, non-absorbables must be removed or they will lead to chronic sepsis.

Monofilament and Multifilament

A further subdivision of suture materials is Monofilament and Multifilament. A monofilament suture is made of a single strand. It resists the harboring microorganisms and it ties smoothly, which can ease the judgment of the tightening of a knot but can also lead to knot slippage. A multifilament suture consists of several filaments twisted or braided together. This gives good handling and tying qualities.

Natural and synthetic

Natural sutures such as silk and catgut are largely being replaced by synthetic materials. There is a case for suggesting that they should no longer be used.


SUTURE MATERIALS:

Vicryl
Braided synthetic absorbable suture Polyglactin 910 Retains 70% of initial strength at 10 days and 30% at 20 days Complete absorption in 60 - 90 days

Coated Vicryl
As Above
Coated with a mixture of calcium stearate and polyglactin 370 Maintains
100% strength for ~ 45 days and then decreases to 70% by ~ 50 days

PDS
Mono-filament synthetic absorbable suture Polydioxalone
Retains 70% of initial strength for ~ 21 days and is reduced to 50% at ~ 35 days Absorption usually complete within 180 days
Results in minimal tissue reaction

Ethibond
Braided non absorbable synthetic suture
Polyester coated with polybutilate (also a polyester) for lubrication to aid tissue passage with good tissue qualities and tensile strength

Panacryl (Johnson & Johnson)
Braided synthetic absorbable suture
Poly (L-lactide/glycolide) with 90/10 caprolactone/glycolide coating for improved handling.
Retains 60% of it's original strength at 6 months
Complete absorption takes 1.5 to 2.5 years
The Breaking Strength Retention (BSR) of VICRYL suture at 3 weeks is 50%, compared to 90% for PANACRYL suture after 6 weeks. At 3 months, the BSR of VICRYL suture is zero, whereas PANACRYL suture has a BSR of 80%. PANACRYL suture still retains 20% of its BSR after 1 year. The BSR is 25% at 6 weeks for MAXON, and 64% at 6 weeks for PDS II suture.  

Orthocord (Johnson & Johnson)
Non-absorbable braided suture
Composite suture composed of dyed absorbable polydioxnone (PDS) (62%) and un-dyed non-absorbable polyethylene (38%). The partially absorbable suture is coated with a vicryl copolymer of 90% caprolactone and 10% glycolide.
55lbs of tensile strength and 30lbs of knot strength

The advantage of such a semi-biodegradable suture is that:

  1. It is less stiff than other similar sutures with better handling properties
  2. May reduce cutting through poor quality tissue
  3. The PDS resorption leaves space for tissue ingrowth and encapsulation
  4. Soft tissue replacing PDS will provide load-bearing benefit, whilst transferring to load-sharing during healing
  5. No particles or fragmentation in the tissue at 18 weeks

Orthocord retains it's strength in-vivo:

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Fiberwire (Arthrex)
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Catgut
Intestinal submucosa of sheep and intestinal serosa of cattle
Retains tensile strength for ~ 10 days

Chromic Catgut
(Chromatised) retains tensile strength for 20 - 40 days

Both forms of catgut result in a moderate tissue reaction

Proline
Non absorbable synthetic mono-filament suture Polypropylene (extruded)
Low tissue reaction and easy tissue passage 

Nylon
Non absorbable synthetic mono-filament suture

Silk
Natural silk is made up 70% of protein fibre and 30% extraneous material such as gum Processing involves degumming
Protein make up and extraneous material results in increased tissue reactivity

SUTURE SIZES

Size denotes the diameter of the material. 
Stated numerically, the more zeros (0's) in the number, the smaller the size of the strand.  As the number of  0's decreases, the size of the strand increases.  The 0's are designated as 5-0, for example, meaning 00000 which is smaller than a size 4-0.

USP     Diameter    Tensile Strength (surgeon's knot)
4-0     0.2mm     7.5N
3-0    0.3mm     12.3N
2-0    0.35mm    19.6N
0     0.4mm     22.3N
1     0.5mm     37.3N 

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