Contemporary use of sutures in vascular surgery

Eike Sebastian Debus¹, Ulrich Andreas Dietz²

¹ Department for Vascular Medicine, Vascular Surgery, Angiology and Endovascular Therapy, University Heart and Vascular Centre, Hamburg-Eppendorf, Hamburg, Germany
² Clinic for visceral, thoracic and vascular surgery, Specialisation in Hernia surgery, Bürgerspital Solothurn, Germany

Corresponding author:

Eike Sebastian Debus, MD, PhD

¹Department for Vascular Medicine, Vascular Surgery, Angiology and Endovascular Therapy, University Heart and Vascular Centre, Hamburg-Eppendorf, Hamburg, Germany.

s.debus@uke.de

The choice of surgical suture material depends on two predominant factors: objective criteria defined by its physical properties as well as biochemical properties of the tissue to be sutured. In addition, subjective criteria must be weighed up, which result from handling properties and the surgeon’s preference. Depending on the implantation site (vessel, fascia, fatty tissue) and the surrounding situation (sterile, infected), suture materials are subject to different requirements. Knowledge about suture properties is therefore a prerequisite for application-specific use.

The oldest known records of surgical sutures and wound care date from 3500 BC, described in the Egyptian papyri: animal tendons, braided horsehair, leather strips or cotton fibres were used at that time. Suture techniques in the early days of medicine are closely connected with Hippocrates (460-377 AD) and Cornelius Celsus (around 100 AD). Galen from Pergamon (129-199 PD) was the first to describe an application to stop bleeding, which he called “ligatures”. He recommended gut strings.¹Snyder CC. On the history of the suture. Plast Reconstr Surg. 1976;58(4):401-6.

Over the centuries, there were constant improvements in surgical technique, but development of the suture materials themselves was slow. Infection was a major restriction on new suture materials in medicine. Particularly during the 18th and 19th centuries, more patients fell victim to the transmission of bacteria via foreign body material introduced at operation than to the underlying illness itself.²Snyder CC. On the history of the suture. Plast Reconstr Surg. 1976;58(4):401-6.

It was not until the introduction of antiseptic surgery – where Lord Joseph Lister (1827-1912) played a major role – that the rate of infection declined significantly. (Figure 1)

It was also Lister who, in 1860, created the first special suture material for surgery, the carbol catgut (Figure 2). This marked the beginning of the real era of “professional suture materials”, which from then on underwent rapid development. In 1881 the chromic catgut, disinfected by the same method, followed. The first truly sterile catgut was disinfected by a spore-killing treatment with iodine. In 1909 followed the first industrial scale production by Kuhn and Braun: the Kuhn’sche Catgut.³Dietz UA, Kehl F, Hamelmann W, Weisser C. On the 100th anniversary of sterile catgut kuhn: Franz Kuhn (1866-1929) and the epistemology of catgut sterilization. World J Surg. 2007;31(12):2275-83.

Catgut was obtained from the submucosa of sheep intestine; its special feature was the ability of the material to be absorbed by enzymatic and cellular mechanisms. However, due to its animal origin, catgut led to occasional allergic and severe inflammatory tissue reactions, and the formation of microabscesses was also a frequent occurrence.⁴Echeverria E, Jimenez J. Evaluation of an absorbable synthetic suture material. Surg Gynecol Obstet. 1970;131(1):1-14. Another disadvantage was the considerable swelling effect of the material, which could cause a secondary dissolution of nodules, local ischaemia or even necrosis with septic reactions.⁵Blomstedt B, Jacobsson SI. Experiences with polyglactin 910 (Vicryl) in general surgery. Acta Chir Scand. 1977;143(5):259-63. The wicking effect (capillarity) of catgut also favoured bacterial transport.⁶Thiede A. In-vivo-Untersuchungen bei Nahtreaktionen an sterilen und infizierten absorbierbaren und nicht absorbierbaren chirurgischen Nahtmaterialien. Zentralbl Chir. 1979;104:568-81. Finally, variations in the tearing force caused by an inhomogeneous nature of the thread, had to be accepted. Even if catgut no longer meets today’s requirements, for a long time it was the absorbable suture material of choice. According to an EU Commission Decision of 4.1.2001 (2001/2/EC), catgut of bovine origin may not be used in either veterinary or human medicine as it is classified as specified risk material for the transmission of BSE.

The development of sterile synthetic absorbable suture materials began in the early 1930s. In 1931 an absorbable thread made of polyvinyl alcohol was introduced, and in 1939 a synthetic collagen thread called Collafil was described. In 1939, a coated polyamide thread, the non-absorbable Supramid, was also developed and introduced between 1946 and 1949. This was followed in the 1950s by the development of polyethylene terephthalate ester (polyester), which entered human medicine in 1960. Overall, these high-quality materials were characterised by high tensile strength, low tissue reaction, significantly reduced local inflammatory reaction and favourable handling properties. In addition, the polyester thread was also very well suited for radiation sterilisation, which was developed around the same time for suture materials.

In the second half of the 1960s, a new era of absorbable sutures began with the development of polyglycolic acid thread (PGS). The suture is made of glycolide polymers. In contrast to catgut, it no longer contains any protein components, so that no cellular or enzymatic reactions take place when polyglycolic acid is broken down. The polymer is broken down exclusively by hydrolysis.⁷Salthouse TN, Matlaga BF. Polyglactin 910 suture absorption and the role of cellular enzymes. Surg Gynecol Obstet. 1976;142(4):544-50. The degradation products can be further metabolised and excreted via the liver and kidneys.⁸Anscombe AR, Hira N, Hunt B. The use of a new absorbable suture material (polyglycolic acid) in general surgery. Br J Surg. 1970;57(12):917-20. It is therefore a material without antigenic or pyrogenic properties; foreign body and inflammatory reactions are kept to a minimum during thread resorption. In addition, the suture shows relatively constant tensile strength with a continuous decrease, so there is less loss of tensile strength in the first days of wound healing than using catgut. A further special feature of the material is the bactericidal and fungicidal effect of its degradation products, glycolic acid, which prevents the transport of bacteria inside the thread and thus the possible spread of inflammation.⁹Thiede A, Jostarndt L, Lunstedt B, Sonntag HG. [Controlled experimental histological and microbiological studies on the inhibitory effect of polyglycolic acid sutures in infections]. Chirurg. 1980;51(1):35-8. ¹⁰Thiede A, Hamelmann H. Moderne Nahtmaterialien und Nahttechniken in der Chirurgie: Springer, Berlin Heidelberg New York; 1982. Between 1970 and 1971 the suture material was introduced worldwide under the name “Dexon” and began to displace catgut as well as other suture materials of plant and animal origin from clinical use. This was the start of regular further developments, including additional coating, ever finer thread strengths or filament diameters etc.

In addition to polymers of pure glycolic acid, another absorbable suture material was developed in the 1970s, polyglactin 910 (Vicryl, Polysorb), whose polymers consist of glycolide and lactide subunits in a 9:1 ratio. These sutures have the same favourable degradation properties as pure PGS. Lactic acid, which is additionally produced during hydrolytic degradation, enters the tricarboxylic acid cycle, where it is further metabolised.¹¹Salthouse TN, Matlaga BF. Polyglactin 910 suture absorption and the role of cellular enzymes. Surg Gynecol Obstet. 1976;142(4):544-50.

Other new developments introduced in the mid-1980s included monofilament sutures made of polydioxanone (PDS) and a polymer made of PGS and trimethylene carbonate (Maxon®). Both show minimal traumatisation and foreign body reactions due to particularly smooth atraumatic tissue penetration, while their composition leads to delayed degradation and thus to maximum tear resistance, especially in the critical phase of wound healing. (Figure 3)

Figure 3. Minimal tissue reaction 3 weeks after polydioxanone implantation (the thread is cut out, LM x 250, HE stain)

An example of the current development is Monocryl®, a mixed polymer of glycolic acid and ε-capronolactone. This thread is characterised by a particularly short absorption time and is therefore reserved for special indications.

The different properties of suture materials allow a classification according to various characteristics. Basically, a classification can be made according to the categories origin, absorbability and processing (“structure”) of the material. An overview is given in Table 1.

A distinction is made primarily between suture materials of organic and synthetic origin. While in the beginning preference was given to organic materials of animal (catgut, animal tendons), vegetable (e.g. twisted yarn, cotton) or mineral origin (e.g. steel), these materials were replaced in the course of time by fully synthetic products made of PGS, polyester, polyamides or polypropylene. This avoided the inflammatory reaction from foreign protein, which is not present in synthetic sutures. Some researchers have even attributed an anti-inflammatory effect to these materials (Table 2).¹Thiede A, Jostarndt L, Lunstedt B, Sonntag HG. [Controlled experimental histological and microbiological studies on the inhibitory effect of polyglycolic acid sutures in infections]. Chirurg. 1980;51(1):35-8.

The classification into absorbable, resorbable and non-absorbable sutures is important. By definition, absorption characterizes degradation by hydrolysis (synthetic sutures), whereas resorption (organic sutures) occurs when degradation is linked to cellular and enzymatic mechanisms. The latter is usually accompanied by stronger tissue reactions. These are mainly products of animal or plant origin, the main components of which are foreign proteins and thus have a more or less strong allergenic potency. In addition, a distinction is made between sutures that are absorbable in the medium term and those that are absorbable in the short term, according to the dissolution and function time. However, this terminology does not differentiate between absorption and resorption. An overview is provided by Table 3.

The function time describes the time until the suture material has reached a measurable loss of tensile strength, while the dissolution time indicates the time until the thread is completely dissolved. For example, the monofilament sutures Maxon® and PDS® have a function time of around 8 weeks and a dissolution time of 6-8 months on average belong to the “maS”, while sutures made of pure PGS or PG 910 (e.g. Vicryl®, Polysorb®) with a function time of around 4 weeks and a dissolution time of a maximum of 5 months belong to the “saS”. A special form of “saS”, threads with a particularly fast function time of a maximum of 14 days should be mentioned. These are called ultra-short term absorbable sutures (usS), which are therefore reserved for specific indications (Monocryl®, Vicryl rapid®).²Debus ES, Geiger D, Sailer M, Ederer J, Thiede A. Physical, biological and handling characteristics of surgical suture material: a comparison of four different multifilament absorbable sutures. Eur Surg Res. 1997;29(1):52-61.

Different dissolution and function times are a function of the materials used and their special processing. The basic distinction is between monofilament threads (homogeneous, not structured with a completely smooth surface) and polyfilament threads, which consist of a number of individual fibres. Polyfilament threads are available in braided form (fine filaments that are first twisted and then braided around the longitudinal thread core) or in twisted form (single filaments are twisted around the longitudinal axis of the thread). In addition, these threads can be surrounded by a superficial coating, termed a pseudomonofilament, or wrapped in a single-fibre coating (Figure 4).

Figure 4. Thread structures

The processing of the suture material has a considerable influence on tissue permeability as well as handling properties. In contrast to monofilament sutures, a rough (braided) surface, as in uncoated threads, has a distinct sawing effect and thus higher tissue trauma. In addition, braided, uncoated suture materials exhibit capillarity (wicking effect), which could lead to spread of bacteria. A tendency to swelling, with the potential of secondary knot loosening has been described, but this can also lead to local ischaemia or even necrosis in the immediate suture pressure zone. All these effects can be considerably reduced by coating. At the same time, handling is simplified: polyfilament threads generally have more favourable knotting properties, with a better knot fit and thus a higher knotting safety than monofilament materials. Polyfilament threads also have a higher flexibility than monofilament threads, as they are stiffer.

Overall, optimal characteristics of surgical sutures can be summarised, which together define the ideal suture:

– High tensile strength and knot-breaking strength, whereby speed of absorption must not be faster than the critical phase of wound healing

– Minimal tissue reaction

– No influence on function time when used in infected tissue

– Anti-infective

– Reproducible function duration with continuous reduction of the tearing force

– Low capillarity (wicking)

– Low potential for swelling

– Defined reversible extensibility, (reversible adaptation to post-traumatic tissue oedema)

– High flexibility

– Ideal fabric pull-through behaviour (low sawing effect)

– Good knotting properties

– High knot security and good knot tightness

– Low cost

No significant differences in the degradation behaviour of the suture materials is observed at pH values between 7 and 7.4 in vitro. At higher pH-values a tendency towards accelerated degradation is seen in vitro, with significant decreases in Vicryl®. Chu demonstrated a catalytic effect of high pH values on hydrolysis in vitro, but detected the least effect on the behaviour of PGS threads in pH ranges between 7 and 7.44.¹Chu CC. The effect of pH on the in vitro degradation of poly(glycolide lactide) copolymer absorbable sutures. J Biomed Mater Res. 1982;16(2):117-24. ,²Chu CC, Moncrief G. An in vitro evaluation of the stability of mechanical properties of surgical suture materials in various pH conditions. Ann Surg. 1983;198(2):223-8. In biochemical experiments it was shown that E. coli and Proteus have a specific influence on hydrolytic degradation, especially of polyfilament sutures and, to a lesser extent, monofilament sutures. The accelerated degradation of PGS and polyglactin 910 filaments was especially observed after incubation with E. coli and Proteus species.

For aseptic vascular suturing, mainly non-absorbable sutures are used, which are associated with a minimal foreign body reaction. In order to withstand the permanent stress caused by the pulse wave, they should not show any plastic deformation. Polypropylene, for example, meets these requirements. Nevertheless, even non absorbable materials, such as polypropylene, degrade years after implantation. (Figure 5)

Figure 5. Polypropylene thread 6.5 y after human eye implantation; SEM, x 350 (in 11)

A reversible elongation, on the other hand, may be desirable: Some vascular surgeons use polybutester (Novafil, Vascufil) with the idea of a pulse-synchronous, elastic elongation of the thread. Monofilament suture materials lead to only minimal tissue traumatisation due to smooth tissue passage and therefore represent by far the best option for vascular sutures. Braided sutures are no longer considered in vascular surgery. Due to the potential for increased trauma of the sensitive vascular endothelium by their rough tissue passage, they may cause intimal hyperplasia. The higher rigidity and poorer handling properties of monofilament sutures make a more complex loop combination absolutely necessary to achieve a secure knot fit. As a rule, when using polypropylene 6/0 or 7/0 USP 6-8 loops are necessary to achieve a secure knot.

In infectious situations, absorbable synthetic monofilament threads are used; however, a fracture of the suture due to premature bacterial absorption cannot be excluded. Therefore, long-term absorbable suture materials (e.g. polydioxanone) should be used. The rationale behind this concept is the fear that non-absorbable materials may persist as foreign bodies in the area of infection, and thus maintain an infection. However, this hypothesis has not been proven for monofilament polypropylene threads. A braided Vicryl Plus® thread coated with Triclosan is available specially to prevent infection. Triclosan, a polychlorinated phenoxyphenol, is a bacteria-inhibiting agent used in a wide range of medical applications. Vascular suture is always performed with an atraumatic needle-thread combination.

For plastic skin closure, mainly monofilament, non-absorbable suture materials are used in order to ensure smooth and atraumatic tissue penetration and to avoid thread granulomas or excessive degradation reaction. The suture should remain in place as inert as possible until it is removed. Since in the course of primary wound healing, a wound strength corresponding to the environment is achieved within 14 days, absorbable materials with this function time should be used.

The choice of surgical suture material depends on the tissue to be sutured and should be based on the specific properties of the individual sutures. Wherever possible, synthetic absorbable material should be used to avoid a persistent foreign body reaction, except in situations with permanent mechanical stress (vascular suture). Because of the lower tissue trauma and the lack of interfilamentary transport, monofilament threads should generally be preferred to braided threads. However, the poorer knotting function and less favourable handling properties of monofilament sutures must be taken into account.