Equipment / Instruments
Unit 11: Sutures & Other Materials
Topic 6: Suture Selection
A wide variety of suture materials, sizes and needles are now available to the veterinary surgeon. When choosing a suture material, a number of factors need to be considered:
- Initial Strength
- Durability
- Tissue reaction
- Biomechanical Properties
Selection of a suture material includes not only a consideration of the properties of a material, but also the size (gauge) and needle type and size to be used.
Initial strength
A suture should be at least as strong as the tissues into which it is implanted. Conversely the tissues themselves should be strong enough to hold the suture without tearing out if it is to be used as an effective method of apposing tissues during the healing process.
The choice of the suture material depends on both its initial tensile strength and its ability to retain sufficient strength during the healing phase. Generally the initial tensile strength will depend on the material properties themselves and the size or gauge of the material selected.
Suture materials are sized according to USP or metric gauge. The metric gauge is the diameter of the material simply multiplied by 10.
| Actual Size (mm) | Catgut Synthetic | USP Size | Metric Gauge |
|---|---|---|---|
| .02 | 10-0 | 0.2 | |
| .03 | 9-0 | 0.3 | |
| .04 | 8-0 | 0.4 | |
| .05 | 8-0 | 7-0 | 0.5 |
| .07 | 7-0 | 6-0 | 0.7 |
| .1 | 6-0 | 5-0 | 1.0 |
| .15 | 5-0 | 4-0 | 1.5 |
| .2 | 4-0 | 3-0 | 2.0 |
| .3 | 3-0 | 2-0 | 3.0 |
| .35 | 2-0 | 0 | 3.5 |
| .4 | 0 | 1 | 4.0 |
| .5 | 1 | 2 | 5.0 |
| .6 | 2 | 3,4 | 6.0 |
| .7 | 3 | 5 | 7.0 |
| .8 | 4 | 6 | 8.0 |
| .9 | 7 | 9.0 |
The ability of tissues to hold sutures depends principally on the collagen content of the tissue and the orientation of the collagen within these tissues.
Skin and fascia have a high collagen content and therefore are very capable of holding sutures. Whilst tendons are also very high in collagen content, the collagen fibres are very highly orientated and therefore have less holding power along their fibres than across their fibres, a fact that significantly effects the selection of suture pattern in approximating the ends of a cut tendon. Fat is the weakest tissue of all.
Visceral tissues, on the other hand, have a holding strength intermediate to that of skin and fat. The stomach and small intestine are however somewhat stronger than either the bladder or colon.
Durability
Properties of Absorbable Suture Materials
The loss of suture strength of absorbable sutures should optimally lag slightly behind the gain of strength in a healing wound.
| Absorbable suture material | Loss of Tensile Strength* | Absorption | Knot Security |
|---|---|---|---|
| Natural: Chromic Catgut | 33% - 7 days 67% - 28 days |
60 days | Good - Dry Poor - Wet |
| Natural: Collagen | 60 days | ||
| Synthetic Multifilament: Polyglactin 910 (Vicryl) | 35% - 14 days 60% - 21 days |
60 - 90 days | Fair/Good |
| Synthetic Multifilament: Polyglycolic acid (Dexon) | 35% - 14 days 65% - 21 days |
60 - 90 days | Fair/Good |
| Synthetic Monofilament: Polydioxanone (PDS II) | 30% - 14 days 50% - 28 days 75% - 42 days |
182 days | Good |
| Synthetic Monofilament: Polyglyconate (Maxon) | 25% - 14 days 50% - 28 days 75% - 42 days |
180 days | Good |
| Synthetic Monofilament: Poliglecaprone (Monocryl) | 40% - 7 days 80% - 14 days |
90 - 110 days | Good |
Properties of Non-absorbable Suture Materials
| Non-absorbable suture material | Loss of Tensile Strength* | Absorption | Knot Security |
|---|---|---|---|
| Natural: Silk | 30% - 14 days 50% - 1 year |
2+ years | Fair |
| Natural: Linen | 50% - 120 days | N/A | Good |
| Synthetic Multifilament: Polyester | N/A | N/A | Poor |
| Synthetic Multifilament: Coated Caprolactam | N/A | N/A | Good |
| Synthetic Monofilament: Nylon | 30% - 2 years | N/A | Good |
| Synthetic Monofilament: Polypropylene | N/A | N/A | Fair |
| Synthetic Monofilament: Polybutester | N/A |
N/A | Good |
| Synthetic Monofilament: Stainless Steel | N/A |
N/A | Good |
*These figures are quoted by the suture manufacturers for rat subcutaneous implants.
Durability
Tendons and ligaments heal very slowly and are often subject to significant tensile forces unless steps are taken to minimise these. Non-absorbable sutures are traditionally used for these tissues, although some of the recent long-lasting absorbable materials may be sufficient.
Visceral tissues on the other hand heal relatively rapidly,and most of the absorbable suture materials have sufficient durability.
General and local host factors such as hypoproteinaemia, infection or gastric enzymes may also significantly alter either the loss of tensile strength of the suture material or the gain in strength of the healing wound, or both, and therefore significantly influence the selection of the material used.
Catgut is very unpredictable in its rate of absorption, and in the presence of infection or gastric enzymes may loose its tensile strength due to collagenolysis within days, therefore increasing the chance of wound breakdown and dehiscence.
The synthetic materials are absorbed by hydrolysis and are therefore much more predictable in their performance, however polyglycolic acid (Dexon) rapidly hydrolyses in an alkaline environment and infected urine.
Tendons and ligaments heal very slowly and are often subject to significant tensile forces unless steps are taken to minimise these. Non-absorbable sutures are traditionally used for these tissues, although some of the recent long-lasting absorbable materials may be sufficient.
Visceral tissues on the other hand heal relatively rapidly,and most of the absorbable suture materials have sufficient durability.
General and local host factors such as hypoproteinaemia, infection or gastric enzymes may also significantly alter either the loss of tensile strength of the suture material or the gain in strength of the healing wound, or both, and therefore significantly influence the selection of the material used.
Catgut is very unpredictable in its rate of absorption, and in the presence of infection or gastric enzymes may loose its tensile strength due to collagenolysis within days, therefore increasing the chance of wound breakdown and dehiscence.
The synthetic materials are absorbed by hydrolysis and are therefore much more predictable in their performance, however polyglycolic acid (Dexon) rapidly hydrolyses in an alkaline environment and infected urine.