Raghu S. Athre¹, MD, Jesung Park², MS, and Joseph Leach¹, MD

            The purpose of this project was to compare the tensile strength of nylon, prolene, and fast absorbing gut treated with either peroxide or water for a period of 5 days to emulate a wound care regimen.  An In-Spec 2200 bench top tester was used to find the maximum load that a particular suture could sustain prior to breaking.  Analysis of the data showed a statistically significant decrease in tensile strength of fast absorbing gut treated with peroxide in comparison to fast absorbing gut control samples and to fast absorbing gut samples treated only with water.  Though no in vivo studies were performed, a logical extension of these results would be that premature degradation of fast absorbing gut secondary to usage of peroxide might lead to widened/hypertrophic scars.

Introduction:

Suturing is a critical function in almost all surgical procedures.  The use of suture and the process of suturing have been described in Egyptian scrolls dating from 3500 BC.  The most primitive sutures included silk, leather, and even vegetable fibers¹.  Suture design has evolved a great deal since ancient times, and surgeons now are faced with a plethora of suture options when closing wounds.  The choice of an appropriate suture for a particular situation is based on objective criteria such as absorbability and other physical/chemical properties of the suture; as well as subjective criteria such as surgeon preference.

The variety of wound care regimens following surgical closure of a wound is as numerous as the choices of possible suture types.  Examples of superficial wound care regimens include water, soapy water, bacitracin, bactroban, hydrogen peroxide, Dakin’s solution and any of a variety of combinations of these regimens.  Wound care regimens are also selected based on objective and subjective criteria.  Examples of objective criteria affecting the choice of a regimen may include an open vs. closed wound and cellular toxicity of the wound care agent; whereas surgeon preference and previous experience may subjectively contribute to the decision making process.

Despite the numerous suture and wound care regimen choices, there is a lack of scientific data proving any particular suture or wound care regimen to be vastly superior to another.  The focus of this study was based on an observation in post-surgical head/neck cancer patients.  Due to the equivalent scar profile of absorbable suture to permanent suture and the ability to conserve time and minimize patient anxiety when using absorbable suture, most surgical patients were having the superficial layer of their surgical wounds closed with 5-0 fast absorbing gut^1,2.  The main criterion for deciding whether fast absorbing gut or non-absorbable suture would be used was surgeon preference.  When observed in their 1-week postoperative follow-up, a subset of the patients in whom fast absorbing gut was used had dehiscence of the superficial most layer of skin closure.  In this group of patients, the superficial epidermis would pull apart, and no evidence of the fast absorbing gut sutures could be found.  The separated wound would eventually close over the ensuing 3 to 4 weeks by secondary intention, without any significant complications.  Extensive questioning of these patients revealed that the majority of these patients used hydrogen peroxide to clean their wounds postoperatively.  The question of whether hydrogen peroxide affected the tensile strength of fast absorbing gut by increasing its degradation rate became the focus of this experiment.

Methods:

Fifteen samples of 5-0 fast absorbing gut, 5-0 nylon, and 5-0 prolene suture were obtained from Ethicon, Inc.  These sutures were the same sutures that were sold to hospitals, etc., and all suture packages were checked to ensure that none of the sutures had expired.

All sutures were opened on day 0.  Under each type of suture, 5 samples were randomized to the control group, 5 sutures were randomized to the water group, and 5 sutures were randomized to the peroxide group.  Sutures that were randomized as control sutures did not receive any intervention.  Sutures that were randomized to the water group or the peroxide group were dipped in the appropriate solution twice a day, for five minutes at each trial, for a total of 5 days to simulate a wound care regimen.  For example, a 5-0 Nylon suture in the peroxide group was exposed to peroxide twice a day (morning 0800 and evening 1800) for 5 days.  The peroxide and water solutions consisted of over the counter 3% hydrogen peroxide and distilled water, respectively.

At the end of 5 days, all suture samples were subjected to tensile strength testing using a bench top In-Spec 2200 (Instron Corporation) portable bench top tester.  The In-Spec machine consisted of two jaws that were mobile along a metal rail.  The suture sample was attached to the two jaws, with the jaws being 10 cm apart.  The machine was subsequently triggered and the jaws would begin to pull apart till the suture broke.  The In-Spec machine output variables included a graph of force vs. length of stretch as well as the peak load in kN and various other parameters such as Young’s modulus.  A picture of the testing apparatus is shown in figure 1.

The peak load or breaking strength in kN was tabulated for each trial and mean values were calculated for each group (i.e. Fast absorbing gut_control, Fast absorbing gut_H2O, Fast absorbing gut_H2O2, etc.).  The peak load was the largest load value sustained by the suture prior to breaking.  This value was used as an indicator of the tensile strength of the suture samples.

Following tabulation and calculation of mean values for each group, Microsoft Excel’s statistical package was used to perform a Student’s t-test to determine if performing the various wound care regimens resulted in a statistically significant change in the tensile strength of the suture.  The assumptions for the t-test included a two-tailed t-test with equal variance.

Results:

On preliminary visual examination, nylon and prolene sutures did not appear to be affected by either water or peroxide.  The sutures retained their shape, color, and general feel when handled.  The fast absorbing gut sutures were, however, different.  The fast absorbing gut sutures that were subjected to water did not appear to be affected in comparison to the control sutures.  The fast absorbing gut sutures that were subjected to the peroxide rinses completely disintegrated when handling the suture.  The sutures could not hold any tension at all and, in one case, the suture had completely degraded and the only thing left behind was the needle.

Samples were subjected to tensile strength testing as described above.  Results are shown in Tables 1, 2, and 3.

In conclusion, application of peroxide to the fast absorbing gut resulted in a statistically significant (p<0.05) decrease in the tensile strength of the suture in comparison to control samples and samples subjected to water alone.  Water and peroxide regimens did not affect the nylon and prolene sutures with any statistical significance.

Discussion:

Though wound closure and post-operative wound care regimens are the final steps of most surgical procedures, they are not the least important.  The primary goals of wound closure include obliteration of dead space, approximation of wound edges to create a closed environment separate from the external environment, and maintenance of equally distributed tensile strength over the entire wound surface until tissue tensile strength is adequate to overcome external forces that act to pull the wound apart³.  Furthermore, creating a cosmetically appealing scar that does not affect form or function is as important.  Complications such as wound infection, wound dehiscence, hypertrophic scars, and contractures may result from improper wound closure techniques, improper wound care regimens, and patient factors such as nutritional status and medical comorbidities.

Wound healing is the body’s own defense response to tissue injury and is a complex, inter-related cascade of cellular and chemical events that act in unison to restore tensile strength and appearance of injured skin.  Wound healing is usually described as occurring in three phases: inflammation, proliferation, and maturation.  Though this model is simplistic and does not fully describe the interrelationships between the various phases, it does attempt to develop a framework to understand wound healing.

The inflammatory phase of wound healing is characterized by a vascular and cellular response to injury.  Following injury, exposure of subendothelial collagen and release of neurotransmitters such as epinephrine, norepinephrine, and serotonin leads to aggregation of platelets (i.e. the primary platelet plug).  As platelets adhere to each other, they become activated and release chemotactic and growth factors.  Concurrently, the coagulation cascade is activated by the intrinsic and extrinsic pathways.  The net result of platelet aggregation and coagulation cascade activation is clot formation.  The various chemotactic factors, prostaglandins, growth factors, etc. that are released at the site of injury act to attract various inflammatory cells such as macrophages, T-lymphocytes, and neutrophils.  The inflammatory cells act to cleanse the site of injury, remove necrotic matter, release bacteriocidal free radicals, break down injured tissue, provide cellular and humoral immunity, and secrete substances to attract fibroblasts and angioblasts to the injured area⁴.

The proliferative phase follows the inflammatory phase.  This phase is marked by formation of granulation tissue, epithelialization, angiogenesis, and fibroplasia.  Epithelialization is the formation of an epithelial cell layer over a surface.  This layer occurs within 24-48 hours in most incisional wounds, and provides a seal between the internal wound and the external environment.  Fibroplasia involves the migration of fibroblasts to the injured area and initially starts at about 3-5 days following injury.  Fibroblasts deposit collagen into the wound; tension, pressure, and stress affect the rate of collagen synthesis⁴.

Finally, the maturation process is where the scar assumes its final form.  Collagen remodeling and cross-liking along with removal of old collagen fibers allows the wound to evolve.  Water is reabsorbed from the wound in this stage.  This allows the collagen fibers to lie closer to each other, and therefore facilitates cross-linking and remodeling.  Ultimately, this results in decreased scar thickness.  The peak tensile strength of a wound occurs at approximately 60 days following injury, but the tensile strength of a healed skin wound will only reach 80% of the tensile strength of uninjured skin⁴.

An understanding of the basic steps involved in wound healing allows the surgeon to close wounds without complications, loss of function, or poor cosmetic outcomes.  Similarly, the correct choice of suture is also critically important.  Sutures can be classified under two broad categories: absorbable and nonabsorbable.  Absorbable sutures provide a temporary support scaffold until the wound itself can support the normal stresses and strains of tissue.  Absorption of such sutures can occur by hydrolysis or enzymatic degradation³.  Examples of absorbable suture include Vicryl (polyglactin 910), Monocryl (Poligecaprone 25), Dexon II (polyglycolic acid), PDS (polydioxanone), gut, chromic gut, and fast absorbing gut.  The first stage of absorption occurs with linear kinetics and lasts on the time scale of days to weeks depending on the type of suture.  The second stage of suture degradation, which overlaps the first stage, results in a loss of suture mass.  Nonabsorbable sutures provide a permanent support scaffold and elicit fibroblasts to encapsulate the sutures.  Nonabsorbable sutures are frequently used to close the superficial most layer of skin, and are removed once healing has occurred, but before excessive granulation tissue and scarring around the suture occurs (usually 6-8 days).  Examples of nonabsorbable suture include silk, steel wire, Ethilon (polyamide polymer), Prolene (polypropylene), and Mersilene (polyester)³.  In 1992, Guyuron, et. al. showed that there was no statistically significant difference in usage of absorbable or nonabsorbable suture with respect to hypertrophic scarring when used for superficial closure².

The choices in wound care regimens are as varied as the different choices in types of suture.  A great deal of the selection process in using one regimen over another is based on surgeon preference and surgeon training.  The focus of this paper was to determine the effect of wound care regimens on the tensile strength of suture.  As described above, one of the roles of suture is to provide tensile strength to the wound till the natural tissue mechanisms can heal the wound.  It would subsequently follow that affecting the tensile strength of suture would affect the overall efficiency and outcome of wound healing.

The hypothesis in this experiment was that the use of hydrogen peroxide for superficial wound care caused premature breakdown of superficial fast absorbing gut sutures.  This hypothesis was shown to be true since the tensile strength of fast absorbing gut treated with the peroxide regimen was significantly less than the control samples.  Also, t-test analysis showed the tensile strength of peroxide-treated fast absorbing gut to be significantly less that fast absorbing gut treated with water alone.  There were no significant different differences in tensile strength in the case of Nylon or Prolene sutures with respect to wound care regimen.

From the above information on wound healing, it follows that a loss in tensile strength of suture and widening of the wound incision line could lead to widened or hypertrophic scars.  This observation was not observed in the patients who had premature degradation of their superficial skin sutures.  It is possible that an increased incidence of scarring and poor cosmetic outcome may have been observed if larger patient numbers were observed.  The actual in vivo correlation to what happens when premature degradation of superficial skin sutures was not studied in this experiment.  This shortcoming could be addressed in future experiments by recording and comparing scar results in patients in whom fast absorbing gut with a peroxide wound regimen was used.  Another adjunct to this study could be an animal model where the tensile wound strength as a function of wound care regimen could be measured.

Despite the lack of objective evidence linking peroxide use in patients with fast absorbing gut sutures and an increased incidence of scarring, the evidence from this experiment shows that peroxide significantly decreases the tensile strength of fast absorbing gut sutures.  Therefore, peroxide should be avoided as a superficial wound care regimen where fast absorbing gut sutures are used.  Peroxide does not affect the tensile strength of prolene or nylon sutures.

References:

1. Parrell, G.J. and G.D. Becker.  Comparison of Absorbable with Nonabsorbable Sutures in Closure of Facial Skin Wounds.  Archives of Facial Plastic Surgery.  2003; 5: 488-490.
2. Guyuron, B. and C. Vaughan.  A Comparison of Absorbable and Nonabsorbable Suture Materials for Skin Repair.  Plastic and Reconstructive Surgery.  1992; 89(2): 234-236.
3. Lai, S.Y. and D.G. Becker.  Sutures and Needles.  eMedicine: http://www.emedicine.com/ent/topic38.htm
4. Romo, T. and L.A. McLaughlin.  Wound Healing, Skin.  eMedicine: http://www.emedicine.com/ent/topic13.htm
5. Charbit, Y., Hitzig, C., Bolla, M., Bitton, C., and M.F. Bertrand.  Comparative Study of Physical Properties of Three Suture Materials: Silk, e-PTFE, and PLA/PGA.  Biomedical Instrumentation and Technology.  1999; 33: 71-75.
6. Outlaw, K.K., Vela, R., and Patrick O’Leary.  Breaking Strength and Diameter of Absorbable Sutures after in vivo Exposure in Rat.  The American Surgeon.  1998; 64: 348-354.
7. Debus, E.S., et. al.  Physical, Biological and Handling Characteristics of Surgical Suture Material: A Comparison of Four Different Multifilament, Absorbable Sutures.  European Surgical Research.  1997; 29: 52-61.
8. Quinn, J., Well, G., et. al.  A Randomized Trial Comparing Octylcyanoacrylate Tissue Adhesive and Sutures in the Management of Lacerations.  JAMA.  1997; 277(19): 54-57.
9. Niessen, F.B., Spauwen, P.H.M., et. al.  The Role of Suture Material in Hypertrophic Scar Formation: Monocryl vs. Vicryl-rapide.  Annals of Plastic Surgery.  1997; 39(3): 254-260.
10. Pickett, B.P., Burgess, L.P.A., et. al.  Wound Healing.  Archives of Otolaryngology and Head/Neck Surgery.  1996; 122: 565-569.
11. Guyuron, B. and C. Vaughan.  Comparison of Polydiaxanone and Polyglactin 910 in Intradermal Repair.  Plastic and Reconstructive Surgery.  1996; 98: 817-820.

Acknowledgements:

We would like to cordially thank Danna Ward from Ethicon Corporation for providing free suture samples.  Also we would like to thank the Deparment of Biomedical Engineering at UT-Austin for providing the facilities to test the sutures in this experiment.

Figures:

Figure 1.  Picture of testing apparatus.

Tables:

Table 1.  Tensile strength in kN of fast absorbing gut sutures.

Table 2.  Tensile strength values in kN of Prolene sutures.

Table 3.  Tensile strength values in kN of Nylon sutures.

Table 4. Summary of statistical analysis (BOLD values indicate statistically significance).

¹ Department of Otolaryngology Southwestern Medical School, Dallas, TX

² Department of Biomedical Engineering University of Texas, Austin, TX