Sutures: Past, Present, and Future

We live in a time when polymer chemists work magic with different suture materials to give them specific properties that benefit surgeons. Today's sutures absorb within a consistent time frame every time veterinarians use them, possess specific handling characteristics, demonstrate good knot security, and cause minimal tissue inflammation.

Dean A. Hendrickson

In a perfect world, suture material would be effective in any surgical procedure, possess excellent handling characteristics, display great strength with a small diameter, and exhibit excellent knot security with minimal suture throw. It would also inhibit bacterial growth, cause no tissue inflammation, be absorbed precisely when tissue no longer needs it, and be economical.

Table 1: Characteristics of Commonly Used Suture Materials

While this material doesn't exist yet, the sutures currently available have far surpassed the first silk, cotton, and gut materials to give surgeons many of the desired characteristics just described.

New perspectives

While surgeons have had the option of choosing absorbable or nonabsorbable sutures for some time, they now have the ability to consider other characteristics that can improve the surgical environment for their patients.

Table 2: Absorbable Sutures and Their Rates of Absorption*

For example, suture materials are available for use in rapidly healing tissues, such as the bladder and uterus (Biosyn–Tyco Healthcare/–Kendall Animal Health) and Monocryl–Ethicon). Other sutures are designed with elasticity for better closure of the linea alba (Novafil–Tyco Healthcare/ Kendall Animal Health). There is even suture material available that is impregnated with an antimicrobial agent to help prevent incisional infection (Vicryl Plus with Triclosan–Ethicon).

Figure 1, A ruptured bladder after surgical repair with 2-0 Biosyn suture material, which will be absorbed faster than Maxon or PDS in the rapidly healing bladder wall.

Keep in mind, however, that antimicrobial-impregnated sutures will never take the place of excellent surgical technique, including hemostasis, gentle tissue handling, minimal contamination, and reduced tension on the incision line.

So why are these options important? Because the suture that is easiest for the surgeon to use is not always the best choice for the patient. And that calls for changing your perspective and considering patients first and sutures second.

Figure 2a, Maxon suture material after direct removal from the packet.

The basics of suture materials

In most cases, sutures can be divided into four categories: absorbable, nonabsorbable, monofilament, and multifilament (also known as braided). The different characteristics of each allow practitioners to choose the best suture for a particular application instead of using whatever suture they have on hand.

Table 1

lists the more common suture materials available today.

Figure 2b, Maxon suture material after stretching to reduce memory.

Absorbable sutures. It is well known that different tissues in the body heal at different rates. For instance, the bladder and uterus heal faster than tendons or ligaments. This is due to differences in blood supply and the cell types involved. Consequently, chemists at the major suture companies have developed suture materials that absorb at different rates (Figure 1). Table 2 shows some of the commonly available absorbable sutures. They are listed in order from the most rapidly absorbing suture to the suture that retains its strength for the longest time.

Table 3: Monofilament and Multifilament Suture Characteristics

Synthetic sutures are absorbed through hydrolysis, which is less inflammatory than the absorption process of natural fiber sutures, such as gut. In general, surgeons should use absorbable sutures when they intend to bury the sutures. Absorbable sutures can be used in skin when suture removal would be difficult and when clients are aware that the sutures may remain in place for 60 days or longer.

Nonabsorbable sutures. Generally less inflammatory than absorbable sutures, nonabsorbable suture materials are often used in the skin or buried in areas where the sutures must maintain strength beyond the capabilities of absorbable sutures, as in cranial cruciate ligament repair. If nonabsorbable sutures are required for holding strength beyond the typical absorption time, surgeons should use monofilament nonabsorbable sutures to minimize the inflammatory response.

Table 4: Square knot maximum force to failure

Monofilament and multifilament sutures. Monfilament sutures are generally less reactive than multifilament suture material, but they tend to have more memory, which many surgeons consider detrimental to suture handling. However, surgeons only need to stretch monofilament sutures to reduce the memory (Figures 2a &2b). (Note: Do not pull on the swaged-on needle or it may pull off the suture strand.)

Monofilament sutures generally have less drag when they're pulled through tissue. Theoretically, the smooth nature of the monofilament suture reduces the chance of wicking bacteria into the wound (Table 3). Therefore, I prefer to use a monofilament suture material when placing skin and intestinal sutures. In other instances, a surgeon's preference will often determine the choice of monofilament or multifilament suture material. Personally, I prefer to use monofilament sutures in most cases.

Table 5: Common Suture Uses

Table 4, a compilation of two studies,1,2 shows force-to-failure information (either by knot slippage or suture breakage) for 10 different suture materials and sizes used in a four-throw square knot. Maxon demonstrates excellent knot security and many other positive characteristics, making it my suture choice for all surgical needs except bladder, uterus, and subcutaneous tissue closures, where Biosyn is my suture of choice. Table 5 includes a partial listing of suture materials and common areas of use.

Synthetic vs. nonsynthetic. The majority of commonly used suture materials are synthetic. While nonsynthetic cotton and gut sutures are still available, I don't recommend them. Gut suture material is often less expensive, but it also has negative characteristics that make it a poor choice for most surgical procedures, including a variable absorption time, inflammatory potential, and lack of holding strength. While I realize that gut has been used successfully for a long time and in many different procedures, it can't compete with the benefits of synthetic sutures.

Figure 3, A swaged-on needle (top) and a standard needle with No. 1 Maxon suture material (bottom).

Needle types. Swaged-on needles generally produce less tissue trauma because they are sharper, single-use needles, and less suture material passes through tissue (the suture is not doubled) (Figure 3). In general, a taper needle is best for any tissue other than the body wall or skin. Surgeons should choose a reverse cutting needle instead of a conventional cutting needle to reduce the possibility of suture pull-through.

Figure 4, Small colon anastomosis with a disparate-sized bowel closed in two layers. The first layer was closed with four bursts of a simple continuous suture pattern, and the second layer was closed with two bursts of a minimally inverting Cushing pattern.

Knot geometry and suture size

Knot geometry is an important factor in the volume of buried suture material in a wound. The larger the suture, the greater the volume. The more suture throws, the greater the volume. In one study,3 increasing the size of a multifilament suture from 4-0 to 2-0 resulted in a four- to six-fold increase in knot volume and a three- to four-fold increase in tissue reactivity.

There is no cookbook approach to determining the correct suture size. But in areas such as the body wall, make sure to use a big enough suture to provide adequate holding until the tissue has healed.

Figure 5, A partially closed cannon bone laceration with a near-far-far-near suture pattern using No. 2 nylon suture material.

Using a surgeon's throw will add more foreign material to the wound. Surgeons have known for a long time that adding foreign material to a wound will reduce the number of bacteria necessary for an infectious dose—from an average of 105 bacteria to 104 bacteria per gram of tissue, leading to a greater inflammatory response. The biggest mistake surgeons make is not realizing that suture material becomes a foreign body when used in tissue.

In general, surgeons should use the smallest suture size possible with the least amount of possible throws, and they should only use a surgeon's throw when it's necessary to counteract tension.

Suture patterns

After you've chosen the correct suture type and size, you need to determine the correct suture pattern. There isn't a single right way to determine the proper suture pattern for a specific tissue, but helpful guidelines do exist.

In general, continuous patterns leave less suture material buried in the incision than interrupted patterns. But as you know, if a continuous pattern breaks, the entire incision can fail. In most cases with incisional closure of the bladder, uterus, body wall, or subcutaneous tissue, a continuous suture pattern is adequate.

However, in large horses or cases in which a second abdominal surgery is performed soon after an earlier surgery, surgeons should close the body wall with an interrupted pattern. Closure or anastomosis of the intestinal tract is often accomplished with two to four interrupted bursts of continuous suture patterns (Figure 4). In these instances, the surgeon would begin a pattern and go 1/4 to 1/2 way around the bowel, then tie the suture off and start a new suture. He or she would again go part way around the bowel, tie the suture off, and start again until the entire circumference of the bowel is closed. In cases with disparate sized bowel segments, simple interrupted sutures may allow for better anastomotic integrity.

In areas with a large amount of tension, surgeons should use tension-relieving patterns. While various patterns are available, I prefer using a near-far-far-near pattern. This pattern creates two loops of suture that allow tension realignment, yet it apposes the tissue rather than inverting or everting it. The suture bites are perpendicular to the wound edge making them parallel to the blood supply of the incision (Figure 5).

Vertical mattress sutures can be used if the near bites to the incision are partial thickness, providing better apposition of the incision than with a standard vertical mattress suture pattern. I don't recommend a horizontal mattress suture pattern because two of the suture runs will run parallel to the incision and, consequently, perpendicular to the blood supply of the cut edge.

In summary, we live in a great time with regard to surgery and surgical devices. The major suture manufacturers are committed to providing the best material possible. But until the perfect material is available, it is our responsibility as surgeons to watch for improvements in suture characteristics so we can provide the best care for our patients.

References

1. Carpenter, E.

et al.

: A biomechanical study of ligature security of commercially available pre-tied ligatures versus hand tied ligatures used in equine laparoscopy.

Vet. Surg.

(in press).

2. Shettko, D.; Hendrickson, D.A.: A comparison of the ligature security of commonly used hand-tied laparoscopic slip knots. Vet. Surg. (in press).

3. Van Rijssel, E.J. et al.: Tissue reaction and surgical knots: The effect of suture size, knot configuration, and knot volume. Obstet. Gynecol.74 (1):64-68; 1989.

Suggested reading

Blackford, L.W.; Blackford, J.T.: Suture materials and patterns.

Equine Surgery

, 2nd ed. (J.A. Auer; J.A. Stick, eds.). W.B. Saunders, Philadelphia, Pa., 1999; pp 91-103.

Boothe, H.W.: Selecting suture materials for small animal surgery. Compend. Cont. Ed.20:155-162; 1998.

Campbell, E.J.; Bailey, J.V.: Mechanical properties of suture materials in vitro and after in vivo implantation in horses. Vet. Surg.21 (5):355-361; 1992.

Romfh, R.F.; Cramer, F.S.: Perspectives on sutures. Technique in the Use of Surgical Tools, 2nd ed. (R.F. Romfh; F.S. Cramer, eds.). Appleton & Lange, Norwalk, Conn., 1992; pp 181-208.

Dr. Dean A. Hendrickson joined the equine surgery faculty at Colorado State University as an Assistant Professor in December 1994 and was promoted to associate professor in 2000. He is a diplomate of the American College of Veterinary Surgeons and the Chief of Equine Clinical Services. Dr. Hendrickson is currently authoring a textbook on equine wound management.