According to the current demands on surgical suture materials, the following characteristics are postulated:
- High tensile strength and excellent knot security
- Triggering only minimum tissue reactions/injury
- No capillary effect and thus no swelling in the tissue
- Inhibition of infection
- Minimum elasticity or reversible, predictable elasticity (rubber band effect)
- Good handling (flexibility, suppleness, easy to tie)
- Optimum knot security
- Absorbable
Synthetic non-absorbable suture materials:
- Polyvinyl alcohol (Synthofil®): A joint venture of B.Braun-Melsungen and Wacker-Chemie, polyvinyl alcohol was marketed in 1931 as the first synthetic suture material.
- Polyamides (Nylon®, Perlon®, Supramid®): Polyamide fibers have great strength, suppleness and elasticity and the added advantage that they are hydrophobic and do not swell in water (Braun, B. 1954). However, they do break down after months and years, with the fragments remaining in the body.
- Polyolefins (polyethylene, polypropylene = Synthofil®, Mersilene®)
Synthetic absorbable suture materials:
- Polyglycolic acid: With its high tensile strength and uniform diameter surgeons can use thinner sutures compared to catgut, but still with the same strength (Walsch G. 1976). Unlike catgut, which is broken down enzymatically, PGA is hydrolyzed and gradually metabolized to glycolic acid in tissue, with a functional support period of about 25 days (rapid absorption). The tissue reaction around the suture is much less than with catgut (Artandi C. 1980). The improved version, Dexon-S®, was launched in 1979 (B.Braun-Dexon).
- Polyglactin 910: Introduced in 1974, polyglactin 910 (purple, braided), known as Vicryl®, is a copolymer of glycolic acid and lactic acid (Ethicon). Just like PGA sutures, polyglactin 910 sutures have a functional support period of approx. 30 days and are classified as rapidly absorbable. Vicryl ®rapid is undyed. It is absorbed faster and has high initial tensile strength.
- Polydioxanone (PDS®) and polyglyconate (Maxon®): 1981 saw the first successful production of a monofilament absorbable suture material, polydioxanone (PDS®). In 1983 Lünstedt and Thiede published results of tensile strength tests on the new suture material and noted a medium-term absorption of the suture with a functional support period of 60 to 80 days. Polyglyconate (a mixture of polyglycolic acid and trimethylene carbonate), developed in 1984, exhibits similar characteristics. It is a monofilament and has a functional support period of 40-60 days (Knoop et al. 1987) (Lünstedt B., Thiede A. 1983).
- Poliglecaprone: Poliglecaprone (Monocryl®) was introduced in 1992. It is a monofilament absorbable suture material and commercially available in purple or undyed (for skin sutures). Despite its ultra-short functional support period, it offers high initial tensile strength and a favorable tensile strength profile.
Multifilament
Braided suture material is made by is obtained by interlacing (bobbin lace) thin yarns. In this technique of joining individual strands together to form a stronger thread, the fibers traverse the longitudinal axis of the thread almost at right angles (Nockemann P. F. 1992). Unlike monofilament sutures, braided polyamide sutures are pliable, but also quite elastic. This high elasticity necessitates a certain change in the suture technique and requires three or four throws to tie the sutures securely. (Braun B. 1954)
Monofilament
Monofilament sutures are made of a single thread, have a smooth surface and, unlike multifilament sutures of the same raw material, they are stiffer, i.e., less flexible, than multifilament forms. With thicker sutures, this stiffness, which all monofilament sutures exhibit, makes handling more difficult. Monofilament sutures in particular are more difficult to tie. However, in monofilament sutures the smooth, sealed surface, together with the completely enclosed interior, prevents any capillary effect. At the same time, they excel with very low tissue drag (Nockemann P. F. 1992). All three types of sutures can be traced back to the history of nylon: First marketed was nylon, a monofilament synthetic suture, which exhibited the specific characteristics of nylon as such. Because of the homogeneous material, the clipped ends of the tied suture acted somewhat like spikes. The identified drawbacks of a monofilament suture led to the call for a braided/plied nylon material. Tissue drag should be kept as low as possible. By melting and extruding the polyamides, it was possible to produce bristles and threads of any thickness. Monofilament polyamide sutures, particularly in fine diameters, were marketed for suturing skin, tendons, vessels, and nerves, especially in microsurgery and neurosurgery, as well as ophthalmology (29), and allowed further development and improvement in the surgical specialties.
Pseudomonofilament
Pseudomonofilament sutures can be classified between the two main groups of monofilament and multifilament sutures. Here, the inside of the suture, the so-called core, consists of a multifilament material, which makes the suture supple during handling, especially when tying it. The smooth surface, which gives the suture material its external characteristics, provides a coat-like covering. This may be made of the same raw material as the core of the suture. In other cases, the braided or plied fiber bundles are coated with a thin layer in a separate production step. In general, the thickness of this outer ‘skin’ with its much lower drag coefficient is only 1%-2% of the suture diameter. Usually, the coating is sprayed on after the suture has been produced. This therefore results in a wafer-thin or punctiform coating on the braided/plied suture (Nockemann P. F. 1980).
Polyamides were first marketed as monofilament sutures, and with their special qualities as monofilaments were used in some specialties of surgery. The next stage of polyamide development (particularly for surgical purposes) already led to the production of pseudomonofilament sutures. In 1954, B.Braun gave a lecture on modern plastics and their application in surgery and spoke about modified polyamide sutures: "Supramid, made by Badische Anilin- und Soda-Fabrik, Ludwigshafen, Germany, has its own place between monofilament and braided sutures. This is a plied suture made of Perlon, which is wrapped in a sheath of the same material. Due to its smooth surface it requires multiple throws" (Braun B. 1954).
While the original thread therefore had a braided multifilament structure, the PGA sutures of today are pseudomonofilament, with only very thin sizes still monofilament (Thiede A., Hamelmann H. 1982). Present such sutures have additional coatings, specifically Dexon with polyol, and Vicryl with polyglactin 370 and calcium stearate.
Surface characteristics
Monofilament sutures have a smooth surface and therefore destroys very few tissue cells during suturing. In addition, as homogeneous sutures they do not act as drains, preventing bacterial migration from the skin into the wound.
Coating
Early on in the development of suture materials, there was the desire to have sutures that do not swell when adsorbing wound secretions, thus traumatizing the suture tracks; hence the repeated demand to use strongly and tightly braided, well-waxed sutures.
In the 1960s and 1970s, coatings for non-absorbable sutures were developed, and from the mid-1970s onward, fully synthetic coated, absorbable sutures such as Dexon Bicolor® and Vicryl® became commercially available. The coating also consists of absorbable material.
Smailys et al (1979) coated various medical materials, including suture materials, with antibiotics and heparin by electrophoresis and ultrasound. However, this approach has not reached clinical use yet, although it is also being studied in terms of coating with chemotherapeutics (e.g., to prevent anastomotic recurrence).
Suture materials of the 20th and 21st century, such as PGA coated with polyol and polyglactin coated with polyglactin 370 and calcium stearate, should no longer traumatizesuture tracks (Thiede A. Hamelmann H. 1982).
Swaged and eyed needles
In spring eyed needles a slight tug on the suture will cause it to jump into the eye by itself. An important further refinement of the needle and suture material was the concept and development of the swaged needle, i.e., a smooth permanent connection between needle and suture. These needles have a hollow shank into which the manufacturer has secured the suture by drilling simple holes or whole channels. The suture appears as a direct extension of the needle. This therefore minimizes tissue trauma, since only a small step remains at the end of the swage. The latest development is the so-called pull-off suture, where a slight pull with the needle holder will detach the needle from the suture. The swage zone is designed such that the stitching process itself is not affected, but a force of approx. 3 N to10 N (i.e., 30 g to100 g) will be sufficient to initiate the detachment process. This atraumatic needle-suture combination does away with threading the needle and time-consuming clipping the needle. Originally developed for vascular surgery, this needle-suture combination has now become a permanent fixture in almost all areas of surgical activity (Thiede A., Hamelmann H. 1982). Initially, needle-suture combinations were only supplied single-packaged. Plastic and aluminum foil packages offered a significant improvement: The sutures, already sterilized on the outside, are opened directly for use. The second outer peel-open foil package protects the sterile outside of the inner foil package with the suture, providing the surgeon with a reliably sterile suture.
Surgical suturing - basics and techniques
The different layers of a wound must be reapproximated with interrupted or running sutures. Only suture subcutaneous fatty tissue if the Scarpa fascia is present. Randomized trials studying saphenous vein excision have shown the negative effect of subcutaneous sutures. Additional suture of the fatty tissue leads to tissue ischemia and necrosis and thus increases the risk of infection (P.M Vogt., M.A Altintas, C. Radtke, M. Meyer-Marcotty: Grundlagen und Techniken der chirurgischen Naht [Basics and techniques of surgical suturing], Chirurg 2009 80: 437-447).
Dermal sutures are important because they relieve tension at the wound edges and at the same time provide adequate tensile strength. At present, absorbable suture material is preferred, buried below the dermis by deep dermal needle entry with inverted stitch direction, thus placing the knot subdermally. This measure provides maximum tension relief in the final skin suture. The buried knot reduces the rate of suture extrusion.
Modern synthetic non-absorbable (nylon, polypropylene) and absorbable monofilament sutures (poliglecaprone) minimize tissue reaction and are therefore preferred for wound closure, especially when cosmetic aspects are paramount. One important characteristic of modern suture materials is to trigger as little inflammatory reaction as possible during absorption. Even non-absorbable sutures cause less inflammation than staples.
The suture retention force is determined by the tensile strength of its material. In wounds under low tension, subcutaneous or intradermal running sutures give particularly good cosmetic results. Unlike interrupted sutures, however, they do not allow subtle adjustment of suture tension, which may be necessary in some complex wounds. Hence, subcutaneous running sutures require correctly placed dermal stitches.
Greve et al. demonstrated excellent cosmetic results in more than 1500 absorbable polydioxanone sutures up to 30 cm long. The proximity of the suture material to the epidermis plays a particularly important role here. If the sutures are placed too close to the surface and the mass of the material is also increased by thick knots, this will increase inflammatory reactions. For this reason, with all absorbable interrupted sutures stitching must be clearly subdermal and the wound edges everted: otherwise the running intradermal suture will be too superficial.
Wound closure with tissue adhesive has repeatedly been promoted in recent years. Its clinical application so far has been limited to small superficial wounds and is preferred in children. A recent prospective randomized trial saw a remarkable difference in wound healing. In the tissue adhesive group wound dehiscence occurred in 26% of cases, whereas no dehiscence was observed in the suture group. The authors therefore recommend that in children wounds should better be closed by absorbable intradermal suture.
In a trial by Stockley and Elson, unlike sutures skin staples resulted in a higher rate of inflammatory response, corresponding discomfort during extraction, and less favorable scar formation. The only advantage of staples was the speed of wound closure. Regarding the qualities of absorbable and non-absorbable sutures, no differences in scar formation were seen. However, a trend for better healing was observed with thinner internal subcutaneous sutures. Among the various absorbable materials, monofilament suture material proved to be less reactive than the braided forms.