Goal:
The broad mission of this activity is to train the participant to perform wound closure technique using appropriate sutures and needles.

Objectives:
At the completion of this activity, the participant should be able to:

1. Describe the biomechanical properties and tissue reactivity of surgical sutures.
2. Explain the biomechanical properties of surgical needles.
3. Explain a scientific basis for selecting surgical sutures and needles.

Method of Participation:
To receive credit, participants should, in order, view the objectives, read the educational material, then go to the link at the end of this activity to complete the post-test, evaluation, and then print the CME certificate. This activity should take approximately 1.5 hours to complete. This activity is available through June 30, 2011. No credit will be awarded after this date.

Target Audience:
This educational program is intended for general surgeons as well as other surgical specialists or physicians involved in wound closure.

Accreditation:
The Dannemiller Memorial Educational Foundation is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.

The Dannemiller Memorial Educational Foundation designates this educational activity for a maximum of 1.50 AMA PRA Category 1 Credit(s),^TM. Physicians should only claim credit commensurate with the extent of their participation in the activity.

The Dannemiller Memorial Educational Foundation is an approved provider of the California Board of Registered Nursing. Provider approved by the California Board of Registered Nursing, Provider Number 4229 for 1.8 contact hours.

RNs outside California must verify with their licensing agency for approval of this course

Disclosure Policy:
The Dannemiller Memorial Educational Foundation requires that the faculty participating in a continuing medical educational activity disclose to participants any significant financial interest or other relationship (1) with the manufacturer(s) of any commercial product(s) and/or provider(s) of commercial services discussed in an educational presentation, and (2) with any commercial supporters of the activity. The presenting faculty reported no financial interest or affiliation that impacts on this activity.

Dr. Long has nothing to disclose.

Dr. Lin has nothing to disclose.

Dr. Edlich has nothing to disclose.

The content and views presented in this educational activity are those of the authors and do not necessarily reflect those of the Dannemiller Memorial Educational Foundation or U.S. Surgical. This material is prepared based upon a review of multiple sources of information, but it is not exhaustive of the subject matter. Therefore, healthcare professionals and other individuals should review and consider other publications and materials on the subject matter before relying solely upon the information contained within this educational activity.

FOREWORD
If this educational program heightens the surgeon's interest in the biology of wound closure and infection, the long years occupied in my search for improved methods of wound management would more than fulfill my expectations. Through the ages, selection of surgical sutures, needles and gloves has been an important consideration for surgeons. Despite these important historical considerations, some surgeons perceive surgical suture, needle and glove selection more as an art than as a science. For those artisans, the use of methods and materials for suturing and glove selection is usually a matter of habit, guesswork, or tradition. This approach to suturing has contributed to a growing concern that the suture selection as well as knot tying techniques employed by many surgeons are not optimal and that they incorrectly select sutures and use faulty techniques in tying knots, which is the weakest link in a tied surgical suture. When the recommended configuration of a knot ascertained by mechanical performance tests was compared to those used by board-certified general surgeons, only 25% of surgeons used the appropriate knot construction.¹ Of the twenty-five gynecologists, mostly department heads, who were polled about their knot tying technique, most were convinced that they made square knots, even though their knot-tying techniques resulted in slipped knots that became untied.² When a knotted suture fails to perform its functions, the consequences may be disastrous. Massive bleeding may occur when the suture loop surrounding a vessel becomes untied or breaks. Wound dehiscence or incisional hernia may follow knot disruption.

As with any master surgeon, he/she must understand the tools of his/her profession. This linkage between a surgeon and surgical equipment is a closed kinematic chain in which the surgeon's power is converted into finely coordinated movements that result in wound closure with the least possible scar and without infection. The extensive clinical experience's of the gifted plastic surgeon Kant Lin and trauma surgeon, Dr. William B. Long, were essential ingredients of this empowering continuing education program. Dr. Kant Lin a internationally recognized craniofacial surgeon and Dr. William Long, Medical Director of Trauma Specialists, LLP, have been viewed by many of his colleagues as the Paderewski's of the scalpel who has brilliant results in trauma surgery.

It is my belief that these gifted surgeons have transformed surgical suture and needle selection from a ritual practice to a surgical discipline. Early in my career, surgical selection of sutures and needles was largely based on testimonials and anecdotal experiences of senior surgeons. Today, modern surgeons select sutures and needles on the basis of well-controlled, randomized clinical and experimental trials. Having a keen appreciation of surgical education, they have modeled the format of this course to be an individualized learning environment. The course is designed to teach each participant the scientific basis for suture and needle selection.

Richard F. Edlich, M.D., Ph.D.
Distinguished Professor Emeritus of Plastic Surgery and
Professor of Biomedical Engineering
Founder of the DeCamp Burn and Wound Healing Center
University of Virginia Health Systems
Editor-in-Chief of the Journal of Long-Term Effects of Medical Implants
Director of Trauma Prevention, Education and Research
Trauma Specialists, LLP, Legacy Emanuel Hospital
Portland, OR

INTRODUCTION
There are several different suture materials and needles that provide an accurate and secure approximation of the wound edges. Ideally, the choice of the suture material should be based on the biological interaction of the materials employed, the tissue configuration, and the biomechanical properties of the wound. The tissue should be held in apposition until the tensile strength of the wound is sufficient to withstand stress. A common theme of the many reportable investigations is that all biomaterials placed within the tissue damage the host defenses and invite infection. Because surgical needles have a proven role in spreading deadly blood borne viral infection, the surgeon must select surgical gloves that reduce the risk of accidental injuries during surgery.³

SURGICAL SUTURES
Important considerations in wound closure are the type of suture, the tying technique, and the configuration of the suture loops. Selection of a surgical suture material is based on its biologic interaction with the wound and its mechanical performance in vivo and in vitro. Measurements of the in vivo degradation of sutures separate them into two general classes.⁴ Sutures that undergo rapid degradation in tissues, losing their tensile strength within 60 days, are considered absorbable sutures. Those that maintain their tensile strength for longer than 60 days are nonabsorbable sutures. This terminology is somewhat misleading because even some nonabsorbable sutures (i.e., silk, cotton and nylon) lose some tensile strength during this 60-day interval. Postlethwait⁵ measured the tensile strength of implanted nonabsorbable sutures during period of two years. Silk lost approximately 50% of its tensile strength in one year and had no strength at the end of two years. Cotton lost 50% of its strength in six months, but still had 30-40% of its original strength at the end of two years. Nylon lost approximately 25% of its original strength throughout the two-year observation period.

Nonabsorbable surgical sutures
The nonabsorbable sutures can be classified according to their origin. Nonabsorbable sutures made from natural fibers are silk sutures. Silk sutures are nonabsorbable, sterile, non-mutagenic surgical sutures composed of natural proteinaceous silk fibers called fibroin. This protein is derived from the domesticated silkworm species Bombyx mori of the family bombycidae. The silk fibers are treated to remove the naturally-occurring sericin gum and braided sutures are available coated uniformly with a special wax mixture to reduce capillarity and to increase surface lubricity which enhances handling characteristics, ease of passage through tissue, and knot run-down properties. Silk sutures are available colored black with Logwood extract.

Metallic sutures are derived from stainless steel. Modern chemistry has developed a variety of synthetic fibers from polyamides (nylon), polyesters (Dacron), polyolefins (polyethylene, polypropylene), polytetrafluoroethylene, to polybutester.

Polypropylene is a linear hydrocarbon polymer that consists of a strand of polypropylene, a synthetic linear polyolefin. All polypropylenes begin with a base resin and then go through the following steps: extrusion, drawing, relaxation, and annealing. Each step in the process will influence the ultimate biomechanical performance of the suture. Biomechanical studies demonstrate that the manufacturing process (i.e., annealing, relaxation) can dramatically influence the surface characteristics without altering its strength. Changes in the surface characteristics can facilitate knot construction of the suture. Polypropylene sutures that have a low coefficient of friction will facilitate knot rundown and suture passage through the tissue. A new polypropylene suture has been developed that has increased resistance to fraying during knot rundown, especially with smaller diameter sutures. Polypropylene sutures are extremely inert in tissue and have been found to retain tensile strength in tissues for a period as long as two years. Polypropylene sutures are widely used in plastic, cardiovascular, general, and orthopedic surgery. They exhibit a lower drag coefficient in tissue than nylon sutures, making them ideal for use in continuous dermal and percutaneous suture closure.

Nylon is composed of the long-chain polyamide polymers. While they have a high tensile strength and low tissue reactivity, they degrade in vivo at a rate of about 12.5% per year by hydrolysis. The pliability characteristics of these sutures permit good handling. Because nylon sutures are more pliable and easier to handle than polypropylene sutures, they are favored for the construction of interrupted percutaneous suture closures. However, polypropylene sutures encounter lower drag forces in tissue than nylon sutures, accounting for their frequent use in continuous dermal and percutaneous suture closure. Nylon sutures are also available in a braided construction. These braided nylon sutures are relatively inert in tissue and possess the same handling and knot construction characteristics as the natural fiber, silk sutures.

Polyester sutures are comprised of fibers of polyethylene terephthalate, a synthetic linear polyester derived from the reaction of a glycol and a dibasic acid. Polyester sutures were the first synthetic braided suture material shown to last indefinitely in tissues. Their acceptance in surgery was initially limited because the suture had a high coefficient of friction that interfered with passage through tissue and with the construction of a knot. When the sutures were coated with a lubricant, polyester sutures gained wide acceptance in surgery. This coating markedly reduced the suture's coefficient of friction, thereby facilitating knot construction and passage through tissue. The polyester sutures are coated with either silicone, polybutylene adipate, or teflon.

The polybutester suture is a block copolymer that contains butylene terephthalate (84%) and polytetramethylene ether glycol terephthalate (16%). Polybutester suture has unique performance characteristics that may be advantageous for wound closure.⁶ This monofilament synthetic nonabsorbable suture exhibits distinct differences in elongation compared with other sutures. With the polybutester suture, low forces yield significantly greater elongation than that of the other sutures. In addition, its elasticity is superior to that of other sutures, allowing the suture to return to its original length once the load is removed. In a study by Trimbos et al.⁷ they compared the cosmetic outcome of lower midline laparotomy scars using either nylon or polybutester suture for skin closure. A randomized clinical trial compared polybutester skin suture with that of nylon for lower midline laparotomy wounds in 50 women undergoing gynecologic surgery. Scar hypertrophy, scar width, scar color, the presence of cross-hatching marks, and a total score was assessed in all patients at eighteen months following surgery and compared by nonparametric statistical tests. The wounds closed with polybutester suture were significantly less hypertrophic than those closed with nylon. Regardless of the suture material used, the lower part of the laparotomy scar showed an inferior cosmetic result compared with the upper part underneath the umbilicus for scar hypertrophy, scar width, and the total scar score. The surgeons concluded that polybutester skin suture diminished the risk of hypertrophic scar formation because of its special properties allowing it to adapt to changing tensions in the wound. Increased closure tension of the skin in the midline region above the pubic bone may be caused by a relative immobility of the skin. In 1997, Pinheiro et al.⁸ compared the performance of polybutester sutures to that of nylon sutures in 70 male and female rats in which they examined the clinical response of the skin in abdominal wall muscle to the use of these sutures. Under general anesthesia, standard wounds were created in the dorsum and abdomen of the animals and subjected to suture closure with either polybutester or nylon. The animals were sacrificed immediately, 12, 24, and 72 hours and at four, five and seven days to evaluate the impact of the sutures on the wounds. They found that polybutester suture has some advantages, such as strength, lack of package memory, elasticity, and flexibility which made suturing quicker and easier. They concluded that polybuterster can be used safely on skin and mucosal wounds because it is less irritating to tissues than nylon.

The expanded polytetrafluoroethylene (ePTFE) suture has been expanded to produce a porous microstructure that is approximately 50% air by volume.⁹ The porous nature of the suture allows tissue ingrowth into the suture. The ePTFE suture has some novel performance characteristics that are distinct from those of other monofilament nonabsorbable sutures. ePTFE is more than 100 times more supple than any monofilament suture, without evidence of plastic memory. In addition, the rate of creep (suture elongation that occurs when a suture is subjected to constant load for an extended period) encountered in the ePTFE suture is significantly less than that of the polypropylene suture. These unique features of the ePTFE suture must be weighed against other important considerations. First, the breaking strength of an unknotted and knotted ePTFE suture is significantly less than that of either the polypropylene or polybutester sutures. For either the polybutester or polypropylene sutures, three throws are required to form secure square (1=1=1) knots. In contrast, knot security for a square ePTFE knot is accomplished with seven (1=1=1=1=1=1=1) throws.

The clinical performance of polybutester suture has been enhanced by coating its surface with a unique absorbable polymer.¹⁰ The coating is a polytribolate polymer that is composed of three compounds: gylcolide, epsilon-caprolactone, and poloxamer 188. Coating the polybutester suture markedly reduces its drag forces in musculoaponeurotic, colonic, and vascular tissue. Knot security with the coated polybutester suture was achieved with only one more throw than with comparably sized, uncoated polybutester sutures. On the basis of the results of this investigation, coating the polybutester suture represents another major advance in surgical suture performance.

Only nylon and stainless steel sutures are available both as a monofilament and as a multifilament suture. Monofilament stainless steel is manufactured as different diameter single strands of stainless steel. Multifilament stainless steel sutures are formed by winding one filament around another, forming a twisted suture. Long continuous strands of stainless steel are twisted together to form different gauge sutures. Intertwining three or more filaments forms the other multifilament sutures. Several very fine silk fibers are twisted together to form yarns, which are then braided. The number of silk fibers used regulates the suture gauge. A large gauge suture can be made with braids of synthetic filaments by either increasing the number of filaments or enhancing the size of the filaments.

The ultimate performance of the new cardiovascular sutures and needles must not only be considered as separate entities, but as a complete product with the suture attached to the needle. The introduction and wide acceptance of ePTFE grafts has focused on considerable attention to the bleeding occurring during vascular anastomosis. One of the characteristics of the material is that a needle hole placed in this graft remains approximately the same size as the needle. Needle-hole bleeding is due to the disparity between the diameter of the needle making the hole and the diameter of the suture filling it. With vascular surgical monofilament sutures that have a needle to suture diameter of 2:1, the difference between the sizes of the needles and sutures leaves an unfilled space at each suture hole through which bleeding occurs. To resolve this problem of bleeding through the holes in the ePTFE grafts, a cardiovascular suture made of ePTFE was developed that can be swaged to a taper point needle that closely approximates its suture diameter, having a needle to suture diameter ratio that approaches 1:1. This 1:1 ratio is allowed because of the porous microstructure of the ePTFE monofilament suture.¹¹ Laboratory testing has demonstrated that sutures with a needle to suture ratio of approximately 1:1 encountered less needle hole leakage than sutures with a needle to suture ratio of 2:1. When evaluated with ePTFE graft containing blood maintained at a constant pressure (80 mm Hg), negligible needle hole bleeding was encountered following puncture by a needle with its attached ePTFE suture.¹² A new vascular suture has been designed recently whose diameter also approximates that of its needle diameter, having a needle to suture ratio of 1:1. This vascular suture is a monofilament, polypropylene suture that has been extruded to produce a tapered swage end, which is significantly smaller than that of the remainder of the suture. This tapered suture configuration allows it to be channel swaged to smaller-diameter needles, yielding a needle to suture ratio that approaches 1:1.

Insight into the clinical significance of this needle hole bleeding can be gained from the results of experimental studies in animals. Miller et al.¹³ recorded the volume of canine anastomatotic bleeding in a series of end-to-end, ePTFE graft to ePTFE graft anastomoses made by sutures with different needle to suture diameter ratios. They concluded that sutures with a needle to suture ratio of 1:1 were clinically beneficial, caused reduced blood loss, and limited the time spent in surgery, regardless if ePTFE or polypropylene sutures were used. In contrast, sutures with a needle to suture ratio of 2:1 dramatically increased anastomotic bleeding in ePTFE grafts. With the advent of ePTFE grafts with exterior ePTFE yarn wrap, bleeding around suture holes is a less important consideration.

These unique features of the ePTFE sutures must be weighed against other important features. First, the breaking strength for a knotted and unknotted ePTFE suture is approximately one half that of the polypropylene suture. It is also noteworthy that knot construction in an ePTFE suture did not diminish its breaking strength. This maintenance of breaking strength of the ePTFE suture has also been demonstrated by Miller et al.¹³ In contrast, the breaking strength of polypropylene sutures as well as other sutures tested was decreased by knot construction.¹⁴ The degree of elongation of the unknotted ePTFE and polypropylene sutures before breakage was remarkably similar, and was not influenced by immersion in 0.9% saline solution. After elongation at the different percent extension that did not lead to breakage, the degree of elasticity of the polypropylene sutures, as measured by percent work recovery, was superior to that of ePTFE sutures.

Absorbable surgical sutures
The absorbable surgical sutures are made from either collagen or synthetic polymers. The collagen sutures are derived from the submucosal layer of ovine small intestine or the serosal layer of bovine small intestine (gut). This collagenous tissue is treated with an aldehyde solution, which cross-links and strengthens the suture and makes it more resistant to enzymatic degradation. Suture materials treated in this way are called plain gut. If the suture is additionally treated with chromium trioxide, it becomes chromic gut, which is more highly cross-linked than plain gut and more resistant to absorption. When this treatment of collagen sutures is limited, the result is a special form of chromic gut, mild gut, that is more susceptible to tissue absorption. The plain gut, mild gut and chromic gut sutures are composed of several plies that have been twisted slightly, machine ground, and polished, yielding a relatively smooth surface that is monofilamentlike in appearance. Salthouse and colleagues 15 demonstrated that the mechanism by which gut reabsorbs is the result of sequential attacks by lysosomal enzymes. In most locations, this degradation is started by acid phosphatase, with leucine aminopeptidase playing a more important role later in the absorption period. Collagenase is also thought to contribute to the enzymatic degradation of these collagen sutures.

The type of gut being used determines the rate of absorption of surgical gut. Plain gut is rapidly absorbed. Its tensile strength is maintained for only seven to ten days postimplantation and absorption is complete within 70 days. Mild chromic gut has had a limited exposure to chromium trioxide to accelerate tensile strength loss and absorption. This fast absorbing surgical gut is used primarily for ophthalmic and cuticular applications where sutures are required for only five to seven days. The tensile strength of chromic gut may be retained for 10 to 14 days.

Natural fiber absorbable sutures have several distinct disadvantages. First, these natural fiber absorbable sutures have a tendency to fray during knot construction. Second, there is considerably more variability in their retention of tensile strength than is found with the synthetic absorbable sutures. A search for a synthetic substitute for collagen sutures began in the 1960's. Soon procedures were perfected for the synthesis of high molecular weight polyglycolic acid, which led to the development of the polyglycolic acid sutures.¹⁶ These sutures are produced from the homopolymer, polyglycolic acid. Because of the inherent rigidity of this homopolymer, monofilament sutures produced from polyglycolic acid sutures are too stiff for surgical use. This homopolymer can be used as a monofilament suture only in the finest size. Consequently, this high molecular weight homopolymer is extruded into thin filaments and braided.¹⁶ The thin filaments of polyglycolic acid sutures are coated with POLYCAPROLATE™, a copolymer of glycolide and epsilon-caprolactone, to reduce the coefficient of friction encountered in knot construction. The polyglycolic acid sutures degrade in an aqueous environment through hydrolysis of the ester linkage.

Copolymers of glycolide and lactide were then synthesized to produce a LACTOMER™ copolymer that is used to produce a new braided absorbable suture, POLYSORB™. The glycolide and lactide behaved differently when exposed to tissue hydrolysis. Glycolide provides for high initial tensile strength, but hydrolyses rapidly in tissue.¹⁶ Lactide has a slower and controlled rate of hydrolysis, or tensile strength loss, and provides for prolonged tensile strength in tissue.16 The LACTOMER™ copolymer consists of glycolide and lactide in a 9:1 ratio.

The handling characteristics of the POLYSORB™ sutures were found to be superior to those of the Polyglactin 910™ suture.¹⁷ Using comparable knot construction and suture sizes, the knot breaking strength for POLYSORB™ sutures was significantly greater than that encountered by Polyglactin 910™ sutures. In addition, the mean maximum knot rundown force encountered with the POLYSORB™ sutures was significantly lower than that noted with the Polyglactin 910™ sutures, facilitating knot construction.

The surfaces of the POLYSORB™ sutures have been coated to decrease their coefficient of friction.¹⁷ The new POLYSORB™ suture is coated with an absorbable mixture of caprolactone/glycolide copolymer and calcium stearoyl lactylate. At 14 days postimplantation, nearly 80% of the USP (United States Pharmacopoeia) tensile strength of these braided sutures remains. Approximately 30% of their USP tensile strength is retained at 21 days. Absorption is essentially complete between days 56 and 70.

Drake et al. ¹⁸ recently studied the determinants of suture extrusion following subcuticular closure by synthetic braided absorbable sutures in dermal skin wounds. Miniature swine were used to develop a model for studying suture extrusion. Standard, full-thickness skin incisions were made on each leg and the abdomen. The wounds were closed with either size 4/0 POLYSORB™ or COATED VICRYL™ (Ethicon, Inc., Somerville, New Jersey) sutures. Each incision was closed with five interrupted, subcuticular, vertical loops secured with a surgeon's knot. The loops were secured with 3- throw knots in one pig, 4-throw knots in the second pig, and 5-throw knots in the third pig. The swine model reproduced the human clinical experience and suture extrusion, wound dehiscence, stitch abscess, and granuloma formation were all observed. The cumulative incidence of suture extrusion over five weeks ranged from 10 to 33%. COATED VICRYL™ sutures had a higher mean cumulative incidence of suture extrusion than that of POLYSORB™ sutures (31% vs. 19%). With POLYSORB™ sutures, the 5-throw surgeon's knots had a higher cumulative incidence of suture extrusion than the 3-throw or 4-throw surgeon's knot square, 30% vs. 17% and 10%, respectively. This swine model offers an opportunity to study the parameters that influence suture extrusion. Because the volume of suture material in the wound is obviously a critical determinant of suture extrusion, it is imperative that the surgeon construct a knot that fails by breakage, rather than by slippage with the least number of throws. Because both braided absorbable suture materials are constructed with a secure surgical knot that fails only by breakage rather than slippage with a 3-throw surgeon's knot square (2 = 1 = 1), the construction of additional throws with these sutures does not enhance the suture holding capacity, but plays a key factor in precipitating suture extrusion. Finally, it is important to emphasize that the surgeon must always construct symmetrical surgical knots for dermal subcuticular skin closure in which the constructed knot is always positioned perpendicular to the linear wound incision. Asymmetrical knot construction for dermal wound closure becomes an obvious invitation for suture extrusion.

When coated polyglactin 910 sutures were treated with a pure form of Triclosan, this suture inhibited the growth of bacteria.¹⁹ The addition of the Triclosan to coated polyglactin 910 sutures did not affect physical handling properties and performance characteristics. In addition, this suture did not appear to impair wound healing.²⁰ Finally, the presence of the antibiotic did not influence the absorption of the polyglactin 910 braided sutures.

A monofilament absorbable suture, polydioxanone, has been prepared from the polyester, poly (p-dioxanone).²¹ The results of implantation studies of polydioxanone monofilament sutures in animals indicate that approximately 70% of its original strength remains two weeks after implantation. At four weeks post-implantation, approximately 50% of its original strength is retained, and at six weeks, approximately 25% of the original strength is retained. Data obtained from implantation studies in rats show that the absorption of these sutures is minimal until about the 90th post-implantation day. Absorption is essentially complete within six months.

Another monofilament absorbable suture has been developed using trimethylene carbonate.²² Glycolide trimethylene carbonate is a linear copolymer made by reacting trimethylene carbonate and glycolide with diethylene glycol as an initiator and stannous chloride dihydrate as the catalyst. The strength of the monofilament synthetic absorbable suture, glycolide trimethylene carbonate, is maintained in vivo much longer than that of the braided synthetic absorbable suture. This monofilament suture retained approximately 50% of its breaking strength after implantation for 28 days, and still retained 25% of its original strength at 42 days. In contrast, braided absorbable sutures retained only 1 % to 5% of their strength at 28 days. Absorption of the trimethylene carbonate suture is minimal until about the 60th day post-implantation and essentially complete within six months.

A recent innovation in the development of monofilament synthetic absorbable sutures has been the production of Glycomer 631, a terpolymer composed of glycolide (60%), trimethylene carbonate (26%), and dioxanone (14%). This monofilament suture has many distinct advantages over the braided synthetic absorbable sutures.²² First, this monofilament suture is significantly stronger than the braided synthetic absorbable suture over four weeks of implantation. It maintains approximately 75% of its USP tensile strength at two weeks and 40% at three weeks post-implant. Absorption is complete between 90 to 110 days. In addition, this monofilament suture potentiates less bacterial infection than does the braided suture. The handling characteristic of this monofilament suture is superior to the braided suture because it encounters lower drag forces in the tissue than does the braided suture.

The latest innovation in the development of monofilament absorbable sutures has been the rapidly absorbing CAPROSYN™ suture. CAPROSYN™ monofilament synthetic absorbable sutures are prepared from POLYGLYTONE™ 621 synthetic polyester which is composed of glycolide, caprolactone, trimethylene carbonate, and lactide. Implantation studies in animals indicate that CAPROSYN™ suture retains a minimum of 50-60% USP knot strength at five days post implantation, and a minimum of 20-30% of knot strength at 10 days post implantation. All of its tensile strength is essentially lost by 21 days post implantation.

Pineros-Fernandez et al²⁴ recently have compared the biomechanical performance of CAPROSYN™ suture to that of chromic gut suture. The biomechanical performance studies included quantitative measurements of wound security, strength loss, mass loss, potentiation of infection, tissue drag, knot security, knot rundown, as well as suture stiffness. Both CAPROSYN™ and chromic gut sutures provided comparable resistance to wound disruption. Prior to implantation, suture loops of CAPROSYN™ had a significantly greater mean breaking strength than suture loops of chromic gut. Three weeks after implantation of these absorbable suture loops, the sutures had no appreciable strength. The rate of loss of suture mass of these two sutures was similar. As expected, chromic gut sutures potentiated significantly more infection than did the CAPROSYN™ sutures.

The handling properties of the CAPROSYN™ sutures were far superior to those of the chromic gut sutures. The smooth surface of the CAPROSYN™ sutures encountered lower drag forces than did the chromic gut sutures. Furthermore, it was much easier to reposition the CAPROSYN™ knotted sutures than the knotted chromic gut sutures. In the case of chromic gut sutures, it was not possible to reposition a two-throw granny knot. These biomechanical performance studies demonstrated the superior performance of synthetic CAPROSYN™ sutures compared to chromic gut sutures and provide compelling evidence of why CAPROSYN™ sutures are an excellent alternative to chromic gut sutures.

The direct correlation of molecular weight and breaking strength of the synthetic absorbable sutures with both in vivo and in vitro incubation implies a similar mechanism of degradation. Because in vitro incubation provides only a buffered aqueous environment, the chemical degradation of these sutures appears to be by non-enzymatic hydrolysis of the ester bonds. Hydrolysis would be expected to proceed until small, soluble products are formed, then dissolved, and removed from the implant site. In contrast, the gut or collagen suture, being a proteinaceous substance, is degraded primarily by the action of proteolytic enzymes.

A distinction must be made between the rate of absorption and the rate of tensile strength loss of the suture material. The terms rate of absorption and rate of tensile strength loss are not interchangeable. Although the rate of absorption is of some importance with regard to late suture complications, such as sinus tracts and granulomas, the rate of tensile strength loss is of much greater importance to the surgeon considering the primary function of the suture, maintaining tissue approximation during healing.

When considering an absorbable suture's tensile strength in vivo, we recommend that the manufacturer provide specific measurements of its holding capacity, rather than the percentage retained of its initial tensile strength. The United States Pharmacopoeia (USP) has set tensile strength standards for synthetic absorbable suture material. If the manufacturers were to use these standards to describe maintenance of tensile strength, the surgeon would have a valid clinical perspective to judge suture performance. Some manufacturers persist in reporting maintenance of the tensile strength of their suture in tissue by referring only to the percentage retained of its initial tensile strength, making comparisons between sutures difficult. The need to use USP standards in reporting is particularly important when there are marked differences in the initial tensile strengths of the synthetic sutures. For example, the initial tensile strength of Glycomer 631 is 43% stronger than that of polydioxanone. At two weeks, the Glycomer 631 suture is approximately 30% stronger.

Suture infection-potentiating effect
All sutures damage the local tissue defenses to infection, and several mechanisms are implicated. The trauma of inserting a needle is sufficient to cause an inflammatory response. The surgeon's suturing technique is crucially important. Sutures tied too tightly impair tissue defenses and invite infection.²⁵ Sutures that penetrate the intact skin provide an avenue for wound contamination by means of the perisutural cuff. The presence of the suture material increases the tissue's susceptibility to infection. The magnitude of this local injury to defenses is related to the quantity of suture within the wound (i.e., diameter, length) and to the suture's chemical composition.

The infection potentiating effects of suture materials are listed in Table 1.²⁶ For the absorbable sutures, synthetic monofilament sutures illicit the least inflammatory response followed by the multifilament absorbable sutures. All of the synthetic absorbable sutures were less reactive than the natural fiber absorbable sutures. Of the natural fiber absorbable sutures, plain gut was less reactive than chromic gut.

Similarly, the monofilament nonabsorbable monofilament sutures were the least reactive of the nonabsorbable sutures, followed by the multifilament synthetic nonabsorbable sutures.

Of all sutures, the metallic sutures are the most reactive because of their stiff configuration. Realizing this, the monofilament stainless steel sutures were less reactive than the multifilament stainless steel sutures. The relatively high infection rates encountered with either monofilament or multifilament stainless steel sutures may be the result of their chemical or physical configuration. Stainless steel is not generally as inert as pure polymers and undergoes degradation in vivo. In addition, metallic sutures are so stiff that patient movement induces tissue damage and impairs the wound's ability to resist infection.

Sutures made of natural fibers potentiate infection more than any other nonabsorbable sutures; this correlates with the tissue's reaction to theses sutures in clean wounds.²⁶ It would appear from these experimental studies that the use of silk and cotton should be avoided in wounds that have experienced gross bacterial contamination. Furthermore, because the handling characteristics of the highly reactive natural fiber sutures are indistinguishable from those of the less reactive braided nylon sutures, we believe that there is no clinical role for these natural fiber sutures in surgery.

The physical configuration of a suture has a significant role in the development of infection. Using a model similar to that reported by our laboratory, Sharp and colleagues²⁷ found that the synthetic monofilament sutures were associated with less infection than that encountered with the multifilament synthetic sutures exposed to the same bacterial inocula. The superiority of the synthetic absorbable sutures over the naturally occurring gut sutures was also evident with this model.

In general, the techniques of sutural closure of skin can be divided into two types: percutaneous sutures and dermal (subcuticular) sutures. The selection of the technique for closure is influenced by the wound's configuration and biomechanical properties, as well as other special circumstances. Percutaneous sutures of either monofilament nylon or polypropylene are excellent for closure of skin wounds because these suture materials exert the least damage to the wounds' defenses.⁴ Because the magnitude of the suture's damage to the local tissue defenses is related to the quantity of the suture within the wound (i.e., diameter, length), we employ the narrowest diameter suture (5-0 or 6-0) whose strength is sufficient to resist disruption of the skin wound. By approximating the middle portion and the bisected portions of the unclosed wound with percutaneous sutures, the least length of suture can be employed in the skin closure. An interrupted dermal suture placed in each quadrant of a wound subjected to strong static and dynamic skin tensions provides sufficient strength to permit early suture removal. Sutural closure of the adipose tissue beneath the skin should be avoided.²⁸ Obliteration of this potential dead space between the cut edge of adipose tissue by even the least reactive suture increases the incidence of infection.

When wounds of different thickness are to be reunited, the needle having passed through one edge of the wound should be drawn out before reentry through the other side of the wound. This maneuver will ensure that the needle will be inserted at comparable levels on each side of the wound. Unless appropriate adjustment of the bite is made on the thinner side, uneven coaptation of the skin will occur resulting in a step-off scar. Grasping or crushing of the skin edges by forceps should be avoided during approximation of the wound.

Dermal (subcuticular) sutures can be used alone or as adjuncts to percutaneous sutures in wounds subjected to strong skin tensions; they serve as an added precaution against disruption of the wound. Dermal sutures are employed as either interrupted or continuous sutures. Some surgeons prefer a synthetic absorbable suture for dermal closure, whereas others favor a synthetic nonabsorbable suture. When continuous nonabsorbable dermal sutures are employed, the wound is additionally supported with interrupted synthetic absorbable dermal sutures. The continuous nonabsorbable dermal suture is removed before the eighth day after wound closure to prevent the development of needle puncture scars.

In special circumstances, percutaneous sutures should be avoided in favor of dermal sutures: (1) infants frightened at the prospect of suture removal, (2) follow-up appointments are difficult to keep, (3) wounds covered by casts, and (4) patients prone to the development of keloids. When dermal closure alone is used, it is advisable to immediately apply tape skin closures to the wound edges to provide a more accurate approximation of the epidermis.

The influence of dermal suture closure on the wound infection rate is the subject of debate. Certainly, dermal suture closure reduces or completely prevents the normal serosanguinous discharge noted on surgical dressings, which therefore may remain in the wound serving as a culture medium for bacteria. In a prospective clinical trial by Foster and colleagues²⁹ in 127 patients after appendectomy, wound infections were significantly more common after dermal polyglycolic acid sutures than in wounds approximated by percutaneous interrupted nylon sutures. In another clinical study by Hopkinson and Bullen³⁰ involving 184 patients after appendectomy, the infection rate in wounds after interrupted dermal polypropylene sutures did not differ from that of wounds approximated by continuous dermal polypropylene sutures.

There is general agreement, however, that wounds subjected to continuous dermal (subcuticular) closure are more resistant to exogenous bacterial contamination than wounds closed by percutaneous sutures.³¹ The percutaneous suture serves as an avenue for the migration of bacteria from the skin surface into the wound. After infection develops beneath the dermal skin closure, the collecting purulent exudate spreads preferentially between the divided edges of fat rather than penetrating the sutural closure. By the time infection becomes clinically apparent, it has involved the entire extent of the wound. This circumstance is distinct from the localized collections of purulent discharge encountered in infected wounds closed by either interrupted percutaneous sutures or tape. In the latter circumstance, the purulent discharge first exits between the wound edges before spreading between the divided layers of adipose tissue.

Another concern about continuous dermal nonabsorbable sutures is that suture pull-out may require considerable force that may break the suture and may be accompanied by patient discomfort. Several technical considerations may facilitate suture pullout.³² First, polypropylene sutures are advocated over other monofilament nonabsorbable sutures because their surface displays the lowest coefficient of friction facilitating suture removal. In addition, continuous dermal polypropylene sutures should be surfaced as a percutaneous loop every 3 cm to allow shorter segments of the suture to be removed. Suture pullout by elastic traction applied over minutes to hours is considerably easier than suture pullout by manual traction over a short time. Despite the immediate aesthetically pleasing appearance of dermal skin closure, it does not improve the cosmetic appearance of the scar.³³

The type of sutures used to approximate fascia (galea aponeurotica), however, has considerable influence on the width and depth of skin scars. In a study by Nordström and Nordström³⁴ of a group of patients undergoing scalp excision for correction of androgenic alopecia, polypropylene sutures reduced the postoperative stretching and depth of skin scars more than comparably sized polyglycolic acid sutures. Another approach to reducing static skin tensions on the wound is to undermine its edges before closure. Despite common clinical usage of this technique, there has been only one experimental study that objectively evaluated its effects on wound closure. In this in vivo study, McGuire³⁵ identified the directional orientation of the static skin tensions by observing the oval distortion of 6 mm circular skin biopsy sites in pigs. At each location, the immediate change in the shape of the resulting defect indicated the magnitude and directional properties of the static skin tensions. The direction of the static skin tension lines corresponded to the long axes of the defects. Wounds parallel to these static skin tension lines required less force and work to close initially, retracted less with initial excision, and benefited more from undermining than similar wounds oriented perpendicularly to the static skin tension lines. Because undermining the wound margin decreased the forces required for wound closure, it should limit the width of the ultimate scar. This benefit, however, must be weighed against its potential damage to the skin blood supply, which may limit the host's defenses and invite infection. Consequently, we reserve undermining for wounds that are subjected to strong static and dynamic tensions, with low levels of bacterial contamination, during elective surgical procedures.

Suture knot tying
This approach to suturing has contributed to a growing concern that the knot construction employed by many surgeons is not optimal and that they use faulty technique in tying knots, which is the weakest link in a tied surgical suture. When a knotted suture fails to perform its function, the consequences may be disastrous. Massive bleeding may occur when the suture loop surrounding a vessel becomes untied or breaks. Wound dehiscence or incisional hernia may follow knot disruption.

Consequently, the surgeon must develop considerable expertise in tying knots in surgical sutures using either an instrument tie or manual tie techniques. First, the surgeon must have an understanding of the components of a knotted suture loop. Second, he/she must appreciate the mechanical performance of an untied and knotted suture. Important considerations in suture mechanical performance include knot breakage, knot slippage, suture cutting tissue, and mechanical trauma. The surgeon's tying technique remains one of the most important considerations.

Components of a knotted suture loop
The mode of operation of a suture is the creation of a loop of fixed perimeter secured in the geometry by a knot.³⁶ A tied suture has three components (Figure 1). First, the loop created by the knot maintains the approximation of the divided wound edges. Second, the knot is composed of a number of throws snugged against each other. A throw is a wrapping or weaving of two strands. Finally the "ears" act as insurance that the loop will not become untied because of knot slippage. The doctor's side of the knot is defined as the side of the knot with "ears," or the side to which tension is applied during tying. The patient's side is the portion of the knot adjacent to the loop.

Each throw within a knot can be either a single or double throw. A single throw is formed by wrapping the two strands around each other so that the angle of the wrap equals 360°. In a double throw, the free end of a strand is passed twice, instead of once, around the other strand; the angle of this double-wrap throw is 720°. The tying of one or more additional throws completes the knot. The configuration of the knot can be classified into two general types by the relationship between the knot "ears" and the loop (Figure 2). When the right "ear" and loop of the two throws exit on the same side of the knot or parallel to each other, the type of knot is judged to be square (reef). The knot is considered a granny type if the right "ear" and loop exit or cross different sides of the knot. When the knot is constructed by an initial double-wrap throw followed by a single throw, it is called a surgeon's (friction) knot. The configuration of a reversed surgeon's knot is a single throw followed by a double-wrap throw. A knot consisting of two doublewrap throws is appropriately called a double-double.

When forming the first throw of either a square or granny knot, the surgeon is merely wrapping one suture end (360°) around the other, with the suture ends exiting in opposite directions. The surgeon will apply equal and opposing tension to the suture ends in the same planes. The direction of the applied tensions will be determined by the orientation of the suture loop in relation to that of the surgeon's hands. When the surgeon's hands lie on each side and parallel to the suture loop, the surgeon will apply tensions in a direction parallel to his/her forearms (Figure 3). Tension will be applied to the farther suture end in a direction away from the surgeon. Conversely, an equal opposing force will be applied to the closer suture end in a direction toward the surgeon. After constructing the second throw of these knots, the direction of the suture ends must be reversed, with an accompanying reversal of the position of the surgeon's hand.³⁷ As the surgeon's hands move toward or away from his body, the movements of his right and left hands are in separate and distinct areas that do not cross, permitting continuous visualization of knot construction. With each additional throw, the surgeon must reverse the position of his/her hands.

Orientation of the suture loop in a plane that is perpendicular to that of the surgeon's forearms considerably complicates knot construction (Figure 4). In this circumstance, reversal of the position of the hands occurs in the same area, with crossing and overlapping of the surgeon's hands, temporarily obscuring visualization of knot construction. This circumstance may be encountered when constructing knots in a deep body cavity, which considerably limits changes in hand positions. This relatively cumbersome hand position may interfere with the application of uniform opposing tensions to the suture ends, an invitation to the conversion of a square knot construction to a slip knot.

The granny knot and square knot can become a slip knot by making minor changes in the knot tying technique (Figure 5). Surgeons who do not reverse the position of their hands after forming each throw will construct slip knots. Furthermore, the application of greater tension to one "ear" than the other, encourages construction of slip knots, a practice commonly encountered in tying deep-seated ligatures.³⁸ When the tension is reapplied in equal, and opposing directions, the slip knots can usually be converted into either the square or granny knots.

A simple code has been devised to describe a knot's configuration.³⁹ The number of wraps for each throw is indicated by the appropriate Arabic number. The relationship between each throw being either crossed or parallel is signified by the symbols X or =, respectively. In accordance with this code, the square knot is designated 1=1, and the granny knot 1x1. The presence of a slip knot construction is indicated by the letter S. This method of describing knots facilitates their identification and reproduction. It is, for example, perfectly obvious what is meant by 2x2x2, without giving the knot a name, and all surgical knots can be defined unequivocally in this international language.

Biomechanical performance
The mechanical performance of a suture is an important consideration in the selection of a surgical suture and can be measured by reproducible, biomechanical parameters.⁴⁰ The suture's stiffness reflects its resistance to bending. Its coefficient of friction is a measure of the resistive forces encountered by contact of the surfaces of the suture material during knot construction. Strength is a key performance parameter that indicates the suture's resistance to breakage. The knot breakage load for a secure knot that fails by breakage is a reliable measure of strength. During these tests, forces are applied to the divided ends of the suture loop. As the suture is subjected to stress, it will elongate. The load elongation properties of a suture have important clinical implications. Ideally, the suture should elongate under low loads to accommodate for the developing wound edema, but return to its original length after resolution of the edema. Although it should exhibit an immediate stretch under low loads, it should not elongate any further while continuously maintaining the load, exhibiting a resistance to creep.

These biomechanical parameters play important roles in the clinical performance of the suture. Surgeons consider the handling characteristics of the suture to be one of the most important parameters in their selection of sutures. Surgeons evaluate the handling characteristics of sutures by constructing knots using manual and instrument-tie techniques. The surgeon prefers a suture that permits two-throw knots to be easily advanced to the wound edges, providing a preview of the ultimate apposition of the wound edges. The force required to advance the knot is called knot rundown force. Once meticulous approximation of the wound edges is achieved, the surgeon prefers to add one more throw to the two-throw knot so that it does not fail by slippage.

The magnitude of the knot rundown force is influenced considerably by the configuration of two-throw knots.⁴¹ Knot rundown of the surgeon's knot square (2=1) generates sufficient forces to break the knot. In contrast, knot rundown of square (1=1), granny (1x1), and slip (S=S, SxS) knots occurs by slippage. For comparable sutures, the mean knot rundown force for square knots is the greatest, followed by that for the granny (1x1) knots, and then the slip (S=S, SxS) knots.

Failure of the knotted suture loop may be the result of either knot slippage or breakage, suture cutting through tissue, and mechanical crushing of the suture by surgical instruments. Initially, the knotted suture fails by slippage, which results in untying of the knot. All knots slip to some degree, regardless of the type of suture material. When slippage is encountered, the cut ends ("ears") of the knot must provide the additional material to compensate for the enlarged suture loop. When the amount of knot slippage exceeds the length of the cut "ears," the throws of the knot become untied. In general, surgeons recommend that the length of the knot "ears" be 3 mm to accommodate for any knot slippage. Dermal sutures are, however, an exception to this rule. Because the "ears" of dermal suture knots may protrude through the divided skin edges, surgeons prefer to cut their dermal suture "ears" as they exit from the knot. It must be emphasized that knot security is achieved in a knot without "ears" with one more throw than in a comparable knot whose "ear" length is 3 mm.

Knot slippage
Knot slippage is counteracted by the frictional forces of the knots. The degree to which a knot slips can be influenced by a variety of factors including the coefficient of the friction of the suture material, suture diameter, moisture, knot type and final geometry. Knots of the granny type (crossed) usually exhibit more slippage than do knots with a square-type (parallel) construction.

With each additional throw, incrementally greater forces are required for knot untying. After a specified number of throws, failure will occur by knot breakage, after which the knot breakage force will not be enhanced by the addition of more throws. Consequently, these additional throws offer no mechanical advantage and represent more foreign bodies in the wound that damage host defenses and resistance to infection.

The human element in knot tying has considerable influence on the magnitude of knot slippage.³⁷ The amount of tension exerted by the surgeon on the "ears" of the knot significantly alters the degree of slippage. The careless surgeon who applies minimal tension (10% of knot break strength) to the "ears" of the knot constructs knots that fail by slippage. Knot slippage can be minimized by applying more tension (80% of knot break strength) to the "ears" of the knot. Another serious error often made by the inexperienced surgeon is not changing the position of his/her hands appropriately during construction of square and/or granny type knots. The resulting knot, a sliding or slip knot, will become untied, regardless of the suture material. The risk of forming a slip knot is greatest when tying one-hand knots and/or with deep seated ligatures.^41,42

Knot breakage
When enough force is applied to the tied suture to result in breakage, the site of disruption of the suture is almost always the knot. The force necessary to break a knotted suture is lower than that required to break an untied suture made of the same material.³⁶ The forces exerted on a tied suture are converted into shear forces by the knot configuration that break the knot. The percentage loss of tensile strength, as a result of tying a secure knot, is least with monofilament and multifilament steel.⁴³ This relationship between the tensile strength of unknotted and knotted suture, which is designated knot efficiency, is described in the following equation:

Regardless of the type of suture material, the efficiency of the knot is enhanced with an increasing number of throws, although only up to a certain limit.

The type of knot configuration that results in a secure knot that fails by breaking varies considerably with different suture material. The magnitude of force necessary to produce knot breakage is influenced by the configuration of the knotted suture loop, type of suture material, and the diameter of the suture.³⁶ The tissue in which the suture is implanted also has considerable influence on the knot strength of suture. In the case of absorbable sutures, a progressive decline in knot breaking strength is noted after tissue implantation. In addition, the magnitude of knot breakage force is significantly influenced by the rate of application of forces to the "ears" of the knot.⁴¹ When a constant force is applied slowly to the knot "ears," the knot breakage force is significantly greater than that for knots in which the same constant force is applied rapidly to the "ears." The latter knot loading rate is often referred to as "the jerk at the end of the knot," especially when the knotted suture breaks.

Suture cutting tissue
Suture failure also may occur if the knotted suture loop cuts through the tissue. The type of tissue has considerable influence on the magnitude of force required to tear the suture through the tissue. Howes and Harvey⁴² reported that the forces required to tear gut sutures through canine fascia was the greatest followed by muscle, peritoneum and then fat. Using cadaver specimens six to 93 days after death, Tera and Åberg⁴⁴ measured the magnitude of forces required for suture to tear through excised musculoaponeurotic layers of laparotomy incisions. The rationale for this study was that the forces required to tear sutures through a musculoaponeurotic layer would provide a basis for the choice of a suture whose strength is at least as strong as the forces required to tear the suture through the tissue. When the suture was passed lateral to the transition between the linea alba and the rectus sheath, the force required to tear the suture through the tissue was greater than that for any other musculoaponeurotic layer tested; the paramedian incision required the lowest forces to pull sutures through its sheaths. When they recorded the forces needed for sutures to tear through structures involved in the repair of inguinal hernia, the structures making up the conjoined tendon and Cooper's ligament were the strongest and exhibited twice the resistance to suture tearing than those of the other structure.

As expected, the force required for sutures to tear through tissue changes during healing. Åberg⁴⁵ reported that the forces needed for sutures to tear through the aponeurotic muscle layer reduced significantly during the first week of healing. When the wound edges were approximated by sutures tied tightly around this aponeurotic muscle layer, the reduction in force needed for the suture to pull through this tissue persisted for two weeks.

Mechanical trauma
Mechanical trauma to the suture by surgical instruments can also result in suture failure. Nichols et al⁴⁶ cautioned surgeons about the handling of sutures by surgical instruments. They indicated that either the application of clamps and forceps to sutures or rough handling of sutures could damage and weaken them. Stamp et al⁴⁷ incriminated the teeth in the needle holder jaws as important causal factors of sutural damage. Compression of sutures between the needle holder jaws with teeth produced morphologic changes in sutures that resulted in a marked reduction in the suture breaking strength. Similarly, the sharp edges of needle holder jaws without teeth can even crush the suture and thereby decrease its strength.⁴⁸ Finally, application of large compressive loads by pinching polypropylene sutures with DeBakey forceps decreased the strength of the suture.⁴⁹

Tying technique
The surgeon may use an individual ligature ("free tie") or a suture that is attached to a needle or ligature reel. The length of a free tie or suture attached to a needle is usually 18 inches. The longest strands of suture material are available on a reel or spool. When the suture is attached to a needle or reel, there is a free end and a fixed end; the fixed end is attached to either the needle or reel. The first throw of a knot is accomplished by wrapping the free end either once or twice (surgeon's) around the fixed end. During practice, clamp one end of the suture with an instrument that serves to represent either the needle or the reel, which is the fixed end of the suture.

Formation of each throw of a knot is accomplished in three steps. The first step is the formation of a suture loop. In the second step, the free suture end is passed through the suture loop to create a throw. The final step is to advance the throw to the wound surface. For the first throw of a square, granny, and surgeon's knot square, tension is applied to the suture ends in opposite directions. With each additional throw, the direction in which tension is applied to the suture ends is reversed. The surgeon should construct a knot by carefully snugging each throw tightly against each other. The rate of applying tension to each throw should be relatively slow.

For either the square knot or surgeon's knot square, the direction in which the free suture end is passed through the loop will be reversed for each additional throw. If the free suture end is passed down through the first suture loop, it must be passed up through the next suture loop. Reversal of the direction of passage of the free suture end through the loop does not alter either the knot's mechanical performance or its configuration. It simply reverses the presentation of the knot. For granny knots, the direction in which the free suture end is passed through the loop is the same for each additional throw.

During surgery, knot construction involves two distinct steps. The purpose of the first step is to secure precise approximation of the wound edges by advancing either a onethrow or a two-throw knot to the wound surface. Once the throw or throws contact the wound, the surgeon will have a preview of the ultimate apposition of the wound edges. Ideally, the knotted suture loop should reapproximate the divided wound edges without strangulating the tissue encircled by the suture loop. If there is some separation of the wound edges, the one-throw or two-throw knot can be advanced to reduce the size of the suture loop and thereby bring the wound edges closer together.

When the surgeon forms a double-wrap throw, the first throw of the surgeon's knot square (2=1) can maintain apposition of the wound edges by "locking" or temporarily securing it in place by reversing the direction of pull on its "ears." The "locked" double throw is not a reliable means of maintaining wound apposition because any tension applied to the "ears" from the patient's side of the knot will unlock the knot. The addition of the second throw to the surgeon's knot square (2=1) will provide additional resistance to wound disruption, but this knot will not advance by slippage, limiting the surgeon's ability to secure meticulous coaptation of the wound edges.³⁸

In contrast, two-throw square (1=1) or granny (1x1) knots can be advanced to the wound surface to secure precise wound edge apposition. These two-throw square (1=1) or granny (1x1) knots can be easily converted into their respective slip knots by applying tension to only one "ear" in a direction that is perpendicular to that of the tissue surface. Square (S=S) or granny (SXS) slip knots require lower knot rundown forces for knot advancement that either the square (1=1) or granny (SXS) slip knots require lower knot rundown forces for knot advancement than either the square (1=1) or granny (1X1) knots, but will never reach knot security even with 5 throws.⁴¹ Surgeons may inadvertently construct slip knots when tying knots with one-hand technique or forming knots in deep cavities.⁴¹ The risk of tying slip knots can be obviated by applying tensions to both "ears" in horizontal planes parallel to the tissue surface.

The second step in knot construction is the addition of a sufficient number of throws to the knot so that it does not fail by slippage. The magnitude of knot breakage force is always greater than that for knot slippage force of a comparable suture, ensuring optimal protection against wound dehiscence.

Instrument tie
Knot construction can be accomplished by either an instrument or hand tie.⁴⁸ An instrument tie occurs by the formation of a suture loop over an instrument, usually a needle holder. The right hand holds the needle holder, while the left hand loops the fixed suture end around the instrument. The position of the instrument in relation to the suture ends during knot construction will determine the type of knot. When the instrument is placed above the fixed suture end during the first and second throws, a square-type knot will develop. In contrast, a granny-type knot will first result when the instrument is placed above the fixed suture end for the first throw and then below the fixed suture end for the second throw. By repeating this positioning, the instrument tie is a reliable and easy method to produce multiple throw granny knots (1x1x1), a circumstance not encountered in hand ties. Granny knots with more than two throws cannot be constructed by either the one-hand or two-hand technique, without releasing hold of both suture ends.

Instrument tying is accomplished primarily by the surgeon's left hand, which holds the fixed suture end. Initially, the length of the fixed suture end held by the left hand is long (17 in.), making it difficult to form knots without injuring the attending assistant. This assault can be avoided by shortening the length of the fixed suture end held by the left hand. Preferably, the fixed suture end should be coiled into loops, which are held between the tips of the thumb and index finger. This maneuver is accomplished by first grasping the fixed suture end with the small and ring fingers, while it is being pinched between the tips of the index finger and thumb. By pronating the wrist, a loop forms around the grasped fingers and the top of the loop must again be grasped between the tips of the thumb and index fingers. The small and ring fingers are then withdrawn from the loop before coiling more suture. The grasped suture can be easily lengthened by releasing the coils held between the tips of the thumb and the index finger.

When tying knots with an instrument, it is difficult to apply continuous tension to the suture ends. Consequently, widening of the suture loop due to slippage is frequently encountered in wounds subjected to strong tensions. This technique, however, is ideally suited for closing a wound that is subjected to weak tensions. In this circumstance, instrument ties can be accomplished more rapidly and accurately than hand ties, while conserving considerably more suture. By using this technique, the parsimonious surgeon can complete 10 interrupted suture loops for one suture measuring 18 inches in length. This feat would be impossible if the knots had been tied by hand.

The value of instrument ties has become readily apparent in special situations in which hand ties are impractical or impossible. In microsurgical procedures, an instrument ties provides the most reliable and easiest method of knot construction. When employing suture in the recesses of the body (e.g. mouth, vagina, etc.) or during endoscopic surgery, instruments can also form knots in sites to which the hand could never gain access.

Hand tie
Hand tying of knots can be accomplished by either the two-hand or one-hand technique. Each technique has distinct advantages as well as drawbacks. The two-hand technique of knot tying is easier to learn that the one hand. An additional advantage of the two-hand tie is that the surgeon can apply continuous tension to the suture ends until a secure knot is formed. With the one-hand method, it is often difficult to maintain tension on the suture ends during the formation of the knot and slippage of the first or second throws will be encountered, especially by the inexperienced surgeon. When the surgeon attempts to shorten the resultant enlarged loop by advancing the knot, breakage of the suture may occur, requiring passage of another suture through the once punctured tissue. The student of surgery should master first the construction of square type knots because knot security can usually be achieved with fewer throws than the granny-type knots.⁴⁹ The additional foreign bodies required to form a secure granny knot, predisposes the wound to the development of infection.

The hand-tying techniques illustrated in this manual are those used by right-handed individuals. Using the two-hand technique, he/she constructs the knot predominantly with her/her left hand, which forms a suture loop through which the free suture end is passed. The left hand continually holds the suture end until knot construction is complete. In contrast, the right hand merely holds, releases, and regrasps the free suture end. If the surgeon inadvertently manipulates the fixed suture end with his/her right hand, he/she will be passing either the needle or reel through the formed loop. The latter case is an invitation to needle glove puncture.

Many right-handed surgeons prefer to manipulate the free end of the suture with their left hand during two-hand ties. In such cases, the right hand performs the major manipulation of the suture during formation of the loop. An advantage of this technique is that a surgeon who ties his/her own knots by the two-hand technique during wound closure can hold the needle holder in his/her right hand during knot construction. If one desires to learn to tie knots using the left hand to manipulate the free end of the suture, study the illustrations in a mirror.

Using the one-hand tie, one hand forms the suture loop while manipulating the free suture end. The other hand merely holds the other suture end taut. Most surgeons prefer to manipulate the free suture end with their left hand, allowing them to hold the needle holder in their right hand while they construct knots with their left hand.

There are several important recommendations for selecting a knot tying technique. First, position the hands on each side of and parallel to the suture loop. Second, grasp the appropriate suture ends and form the suture loop, without exchanging suture ends between the hands. While exchanging suture ends between the hands forms a triangular shaped suture loop, it is an unnecessary step that wastes valuable time. Third, pass the free suture end, rather than the fixed suture end, through the suture loop. Finally, reverse the position of the hands after each additional throw. Most of the knot tying techniques in this course comply with these recommendations. However, it is important to point out that the fixed end of the suture is being passed through the suture loops in the two-hand ties. Consequently, the surgeon must detach the needle from the fixed suture end before a two-hand tie.

A standard format for illustrating surgical knot tying techniques has been used throughout this continuing educational course (Figure 6). A horizontal incision is pictured in the top of each illustration. Because the wound edges are subjected to static tensions, there is retraction of the wound edges, with exposure of the underlying tissue. The surgeon is standing facing the wound from the bottom of each illustration. Because the surgeon usually passes the needle swaged to a suture toward himself/herself, the fixed end (black) of the suture with its attached needle enters the farther side of the mid-portion of the wound and exits from the side of the wound closer to the surgeon. The free end of the suture is white to facilitate illustration of the knot tying technique. The suture end (white) to farthest from the surgeon is grasped between the distal phalanges of the left thumb and index finger (tip-to-tip pinch). The tips of the distal phalanges of the thumb and index finger of the right hand grasp the suture end (black) exiting from the wound edge closer to the surgeon. The grasped fingers apply constant tension to the suture ends. The security of this tip-to-tip pinch can be enhanced by grasping the suture ends between the tips of the long fingers (arrow), ring fingers, small fingers, and the palm of each hand (grip activity).

The tying of the square, slip, and surgeon's knots using manual and instrument-tying techniques are illustrated. The technique of tying slip knots has been included in the manual because it is an excellent method to approximate temporarily the edges of wounds subjected to strong tensions. In fact, a slip knot has greater holding power than either a single-wrap or double-wrap throw.⁴⁹ Once there is a meticulous approximation of the wound edges, the slip knot can be converted to a square knot, after which a sufficient number of throws are added to the knot to endure knot security.

Surgical Needles
Surgical needles are produced from stainless steel alloys, which have excellent resistance to corrosion.⁵⁰ All true stainless steels contain a minimum of about 12% chromium, which allows a thin, protective surface layer of chromium oxide to form when the steel is exposed to oxygen. Since their development during the early 1960s, high nickel maraging stainless steels have found extensive use in structural materials in many applications requiring a combination of high strength and toughness. The basic principle of maraging consists of strengthening FeNi martensitic matrices by the precipitation of fine intermetallic phases, such as Ni³Ti. These precipitates are so small that they are only evident on transmission electron microscopy. They strengthen the metal by preventing the planes of atoms in the stainless steel from sliding over each other. A high nickel maraging stainless steel, like S45500, is composed of 7.5% to 9.5% nickel, 0.8% to 1.4% titanium, and 11 % to 12.5% chromium. In contrast, S42000 stainless steel is composed of 12% to 14% chromium without nickel or titanium. Scientists have successfully utilized the concept of high nickel maraging stainless steels (S45500) to develop stainless steel wires with superior strength and ductility for use as surgical needles. Surgical needles made of a high nickel maraging stainless steel have a greater resistance to bending and breakage than stainless steels without nickel.

A new high-nickel stainless steel, SURGALLOY™, has been used recently to manufacture surgical needles.⁵¹ Biomechanical performance studies of cutting edge needles made of S45500 stainless steel alloy and SURGALLOY™ stainless steel demonstrated that needles made of SURGALLOY™ had superior performance characteristics over those made of S45500. The SURGALLOY™ needles had considerably greater resistance to bending than the needle produced from the S45500 alloy. In addition, SURGALLOY™ stainless steel had almost a twofold greater resistance to fracture than the S45500 stainless steel alloy.

Components of the Needle
Every surgical needle has three basic components: swage, body, and point.

Swage
Its swage is the site of attachment of the suture. Since 1914, an eyeless needle, in which the suture was attached to a drilled hole in the needle, has been used. The swaging process provides a smooth juncture between the needle and suture; needles produced by this swaging process thereby created smaller holes in tissue than did threaded eye needles. However, this swaging process was only possible for larger diameter needles (greater than 0.36 mm) because the mechanical drill could not reliably cut uniform holes in the ends of small needles. Consequently, a forming tool was used to create a channel in one half of the diameter of smaller-diameter needles with an underlying receptacle for the attachment of the suture. However, the linear splits in the walls of these smaller diameter needles increased the drag force encountered by tissues during needle passage. With the advent of the laser (yttrium-aluminum-garnet (YAG) laser), uniform holes are reliably produced in the ends of small needles, resulting in a smooth swage that encounters lower drag forces than channel needles.⁵² These low-drag forces caused by laser-drilled needles are associated with minimal mechanical trauma to tissues.

The laser-drilled needles have other unique advantages over the channel needles related to the length of the swage ends. The length of the channel in channel swage needles is four times longer than that of the laser-drilled hole. Because swages are more susceptible to bending and breakage by the needle holder jaws than the body of the needle, surgeons are warned to grasp the needle with the needle holder at a site beyond the swage. In the case of 18 mm long needles with laser-drilled and channel swages, the depths of the laser-drilled holes and channel swages are 1.5 mm and 6.0 mm respectively. The laserdrilled needle can be held by the needle holder jaws 3 mm from the needle end, whereas the channel swage needle is grasped 7.5 mm from the needle end. By grasping the needle close to its end, the surgeon can more easily manipulate the passage of the needle through tissue. This benefit of laser-drilled needles is accomplished without altering the needle suture attachment strength. These distinct advantages of swages produced by lasers indicate that they should eventually replace all channel swage needles.

The needle is attached to the suture by uniformly compressing the walls of the swage against the suture, creating a strong attachment force that prevents the surgeon from detaching the suture from the needle without exerting considerable force on the swage. This suture attachment force is so great that separation of the needle from the suture is accomplished more easily by cutting the suture rather than by applying sufficient force to the suture to separate it from the swage. A special swage has been created by using lower compression forces around the circumference of the swage than conventionally used, allowing the surgeon to detach the suture from the needle using relatively low detachment forces, obviating the need to cut the suture. The swage requiring lower uniform forces to detach its suture is called a variety of names (i.e., pop-off control release). It was originally developed for abdominal wound closure, bolus dressings for skin grafts, and hysterectomies in which large numbers of interrupted sutures are used.

Body
The body of the needle is the portion that is grasped by the needle holder. The security with which needle holder jaws grasp the needle is influenced by the presence of teeth in the needle holder jaws, the ratchet setting of the needle holder handle, and the shape of the cross-sectional area of the needle body. Although the shape of the cross-sectional area of the body has a significant effect on needle holding security, the presence of teeth in the needle holder jaws and the ratchet setting of the needle holder handle are much greater determinants of needle holding security than is the needle body shape.⁵³

The shape of the cross-sectional area and the geometric configuration of the length of the needle can categorize the geometry of the needle body. The shape of its cross-sectional area will influence the security with which the needle holder jaws grasp the needle, as well as its resistance to bending. The cross-sectional areas of the bodies of different needles have the following shapes: circular, triangular, rectangular and trapezoidal. Needles with rectangular cross-sectional areas are created either by flattening the sides of the circular wire or by flattening the top and bottom of the circular wire. When the top and bottom portions of the needle body are flattened, the long axis of its rectangular cross-sectional area will gain intimate contact with the faces of the needle holder jaw. This position of the needle body between the needle holder jaws is similar to that of the needle body with a trapezoidal shape.

In both cases, the needle holding security against twisting and rotation is greater than any other needle body (side flattening rectangular shape, triangular, and circular). This benefit of enhanced needle holding security must be weighed against an associated reduced resistance to bending, as compared to that of the other needle bodies. Because we can increase the needle holding security of all needles by advancing the ratchet setting of the needle holder, we prefer side-flattened needle bodies because they exhibit greater resistance to bending than any other needle body.

The geometry of the length of the needle will have considerable influence on the surgeon's use of a surgical needle. The curvature of the needle is described in degrees of the subtended arc. The radius of the needle is the distance from the center of the needle to the body of the needle, if the curvature of the needle was continued to make a full circle. The curvature of the needle with one radius of curvature may vary from 90° (1/4), 135° (3/8), 180° (1/2), to 225° (5/8). A compound curved needle has two distinct radii of curvature. The type curvature of its tip extends 35° before it assumes a regular uniform curvature in the remaining portion of the needle body (100°).

The surgeon uses needles with a curvature of 135° to approximate divided edges of thin planar structures that are readily accessible (i.e., skin), requiring a limited arc of wrist rotation to pass the needle through the tissue. It is difficult to use the 135° needle in deep body cavities because the limited arc of wrist rotation in passing this needle is usually not sufficient to expose the needle point, so that it will remain buried in the tissue and pose a challenge for the surgeon to retrieve. The 180° needle is ideally suited for use in deep body cavities because a limited arc of wrist rotation will pass successfully the entire needle through the tissue, allowing adequate exposure of the needle point for easy retrieval of the needle by the surgeon. The surgeon uses needles with a 90° angle of curvature in microsurgery.

The compound curved needle has been primarily used to alter the geometry of 135° needles.⁵⁴ The tight needle curvature at the point permits rapid, accurate needle passage at a selected depth and allows controlled exiting. Its design also offers a mechanical advantage over the standard needle with one radius of curvature. Although originally designed for anterior segment ophthalmic surgery, the compound curved needle now has broader clinical applications that include vascular and microvascular surgery, and dermal and skin closure.

In addition to its curvature and radius, a surgical needle can be characterized by three other measurements: chord length, needle diameter, and needle length. Chord length is the linear distance measured from the central point of the needle swage to the point of the needle. The needle diameter is the width of the original circular wire utilized in the manufacturing process for the production of the needle. Needle length is the arc length of the needle measured at the center of the wire's cross-section.

Point
The point of the needle extends from the tip of the needle to the maximum cross section of the body. Each type of needle point is designed to penetrate specific types of tissue. In general, there are needles with cutting edges, taper points, or a combination of both. Cutting edge needles have at least two opposing edges that are designed to penetrate tough tissue. When cutting edge needles have three cutting edges, the position of the third cutting edge categorizes the needle as either a conventional cutting edge needle or a reverse cutting edge needle. Use of the conventional cutting edge needle leaves a hole that is susceptible to tissue cut-through. Because its third cutting edge is on the inside, concave, curvature of the needle, the inside cutting edge causes a linear cut that is perpendicular and close to the incision, against which the suture will exert a wound closure force that may ultimately cut through the tissue. In contrast, the third cutting edge of the reverse cutting edge needle is located on the outer convex curvature of the needle. When the reverse cutting edge needle cuts through skin, it leaves a wide wall of tissue, rather than an incision, against which the suture exerts its wound closure force. This wall of tissue resists suture cut-through.

Specifically designed cutting edge needles have been developed for anterior segment surgery in ophthalmology. These needles received a modification that converted the triangular geometry to a trapezoidal or spatulated configuration by flattening the outer convex surface. This flattening process also produces a lateral widening of the needle body. In addition to ophthalmic surgery, these spatulated needles have been used successfully to repair lacerations of the nail matrix. Referred to as "spatula needles", they are flat on their concave and convex surfaces, with long side-cutting edges. The needle's side cutting edges separate or split through the thin lamellar plane of corneal and scleral tissue with minimal damage.

The sharpness of cutting edge needles is increased by electrohoning, narrowing the needle point configuration, narrowing the cutting edge angles, and by providing a silicone coating. When the needle is electrohoned, the surface of the needle is polished while its edges are sharpened. Narrowing the point configuration of the cutting edge needle will also enhance its sharpness.

The taper point needle tapers to a sharp tip. It spreads the tissue without cutting it. The point geometry of this needle can be measured by its taper ratio, which is the length of the tapered portion of the needle divided by its diameter. The taper ratio of these needles varies from 12:1 to 8:1. They are used in soft tissues that do not resist needle penetration, such as vessels, abdominal viscera, and fascia. They are preferred when the surgeon wants to make the smallest hole possible in tissue without cutting.

All tapercut needles combine the unique features of taper point and cutting edge needles. The cutting edges of the tapercut needle extends only a very short distance from the needle tip and blend into a round taper body. In vascular surgery, tapercut needles are used frequently for the anastomosis of calcified and fibrotic blood vessels to prosthetic grafts. Its cutting tip penetrates the calcified portion of the artery without the cutting edges of the needle body tearing the friable vessel, thereby minimizing the risk of leakage around the needle puncture. Tapercut needles have also been advocated for closure of wounds in the oral mucosa. Its short cutting edges produce a tiny hole in the oral mucosa that is considerably smaller than that encountered with the cutting edge needles. The penetrating point needle is a tapercut needle, used by cardiothoracic and vascular surgeons, that has a diamond shaped point with a small sharp cutting tip. Some surgeons have noted that the penetrating point needle penetrates the calcified tissue of vessels more easily than the standard tapercut needle.

Extensive clinical investigations have demonstrated that blunt tipped surgical needles dramatically reduce the risk of accidental injuries during surgery.³ The standard taper point needle tapers to a sharp point. In contrast, the blunt taper point needle has remarkably similar geometry to that of the taper point needle, except that its point has a blunt ending at the tip of the needle. The geometry of the blunt point needle differs from those of the taper point and blunt taper point needles. Instead of tapering to either a sharp or dull tip, it has no taper at all. Biomechanical performance studies demonstrated that either the taper blunt point or the blunt point needle dramatically enhance the resistance to needle penetration of either single or double gloves.³

The biomechanical performance of surgical needles and needle holders is determined by the following parameters: (1) needle sharpness, (2) needle resistance to bending, (3) needle ductility, and (4) needle holder clamping moment.⁵⁵ A sharpness tester measures the force needed to pass a needle through a membrane that simulates the density of human tissue. Manufacturers measure needle resistance to bending in the laboratory by recording the force required to bend the needle 60° or 90° to determine the needle's ultimate bending moment. The more critical measurement to the surgeon is the needle's yield moment, the force required to irreversibly deform the needle. Ductility is a measurement of the needle's resistance to breakage. The needle holder clamping moment is a measure of the force exerted by the needle holder jaws on a curved surgical needle.

Needle holder
The needle holder is an instrument designed to hold a curved surgical needle. It consists of two first class levers (female and male members) that rotate on a common fulcrum. The portions of the levers that grasp the needle are distal to the fulcrum and are called the jaws. The remaining portion of the lever, that portion which is held by the surgeon, is called the handle. On the end of the handle portion of each shank is a ringlet through which a fingertip can be placed. Once the jaws have gripped the needle, the surgeon can engage a locking mechanism to secure the needle in the needle holder jaws. The locking mechanism consists of individual ratchets with engaging teeth that are attached to each handle next to the ringlets. Once the ratchets are engaged, the needle holder will grasp the needle without the surgeon applying further force to the ringlets because the handles are bent to engage the ratchets, thereby producing a spring force to disengage the ratchets. The angle of each engaging tooth of the ratchet mechanism should be 39° rather than 45° to enhance the security of the engagement of the interlocking teeth.

The box lock is the junction where the female member and the male member are secured, forming the pivoting feature. The box lock is located at the site of the fulcrum of the needle holder. Its surfaces are flat, allowing the lerms to rotate. The chamfer is the edge of the ends of the box lock, being the end edge of the box lock at the jaw and the end edge of the box lock at the handle near the fulcrum. When the needle holder jaws are closed, there should be a space between the opposing chamfer edges so that a suture can slide easily through. In addition, the edges of the chamfer must be rounded to prevent injury to the suture.

Selecting the appropriate needle holder for a designated needle can be accomplished by relating the clamping moment of the needle holder, at the specified ratchet setting, to the yield moment for the needle placed in a measured site in the needle holder jaws. Ideally, the surgeon should use a needle holder whose clamping moment is less that that of the yield moment of the needle. When the clamping moment of the needle holder exceeds the needle yield moment, clamping the needle between the jaws of the needle holder will result in irreversible needle deformation, with a subsequent enlargement of needle chord length.

The design of the needle holder jaw is another important consideration in the selection of a needle holder. Diamond-Jaw® needle holders grasp surgical needles far more securely than conventional needle holders. They feature hard, sharp diamond-cut teeth in inserts of hardened tungsten carbide bonded to the jaw of the instrument. This highly durable insert securely grips the needle, preventing it from rotating or slipping. Tungsten carbide inserts with teeth varying from 2,500 to 7,000 teeth/in2 have been incorporated into the jaws of the needle holder to enhance the jaws' needle holding security.⁵⁶ The presence of teeth within the needle holder jaws limits twisting and rotation of the needle as compared with needle holder jaws without teeth. These teeth stabilize the needle, allowing the surgeon to control accurately the passage of the needle through the tissue.

While appreciating the potential benefits for tungsten carbide jaw inserts with teeth in achieving needle holding security, the surgeon should also realize the potential deleterious effects of the teeth on suture materials and needles. These teeth can produce distinct morphologic changes in monofilament synthetic sutures that markedly reduce the sutures' breaking strength.⁵⁷ The implications of this sutural damage on the strength of continuous monofilament synthetic suture in surgery are obvious. Finally, these teeth can alter the structural configuration of needles by producing stress concentrations, thereby reducing their resistance to either bending or breakage.⁵⁷

Smooth needle holder jaws with rounded edges do not induce structural damage to either the monofilament sutures or needles.⁵⁷ However, their smooth jaw surface provides limited resistance to either twisting or rotation of the needle between the jaws. A textured needle holder jaw metallurgically bonded with tungsten carbide particles (Snowden- Pencer{Division of Cardinal Health}Tucker, GA) appears to be an attractive alternative to both smooth needle holder jaws and those with teeth. 57 Although its needle holding security is significantly less than the jaws with teeth, it provides greater needle holding security than the smooth jaws. By enhancing the average surface roughness of the jaw, the embedded tungsten carbide particles of the textured jaw surface resist twisting and rotational movement of the needle. Unlike the sutural damage inflicted by the jaws with teeth, compression of the synthetic monofilament suture by either the rounded smooth jaws or textured jaws with tungsten carbide particles does not weaken the monofilament suture.

Recent studies demonstrate that the sharp outer edges of some smooth needle jaws cut the smooth surface of the monofilament suture during instrument ties, weakening the strength of the suture. When the smooth needle holder jaws clamp 6-0 monofilament nylon suture with their first opposing teeth, there is a significant reduction in suture breaking strength. This sutural damage can be prevented by mechanically grinding the outer edges of the smooth tungsten carbide inserts, yielding a rounded edge. Clamping the suture with the smooth jaws of the needle holder with rounded edges is atraumatic, with no demonstratable damage to the suture's breaking strength. The sharp edges of the box lock of the fulcrum of the needle holder are another cause of sutural damage during instrument ties. Consequently, the box lock of new needle holders has been manufactured with beveled edges that do not entrap or cut the suture.

Packaging System for Surgical Needles and Sutures
Packages for surgical needles swaged to sutures have been designed to achieve several specific objectives.⁵⁸ First, the package and its contents must be susceptible to sterilization. Second, the package must afford convenient and sterile transfer of the surgical needles swaged to sutures to the sterile field. The needle must be protected to prevent dulling of its cutting edges and point. Finally, the suture must be kept as straight as possible until knot construction.

Each suture swaged to its needle is contained within at least two layers of packaging. These two layers allow sterile transfer to the sterile field. The "breather" or outer pouch is made of a laminate of Tyvek™ on one side and heat sealed to plastic film on the other. The exterior surfaces of this overwrap are not considered sterile. The inside surfaces of the overwrap and primary packet within it are sterile so long as the overwrap remains intact and undamaged. The Tyvek™ backing is permeable to ethylene oxide resulting in reliable gas sterilization of the inside of the overwrap as well as the inner packet containing the suture swaged to the needle. The outer wrap has two flaps that are peeled apart, allowing transfer of the inner packet to the sterile field. The outer wraps for the packages containing either absorbable or nonabsorbable sutures swaged to needles have identical dimensions and construction.

The overwrap has two flaps that are peeled apart, allowing transfer of the inner packet to the sterile field. Once the over wrap is peeled apart, the inner packet is transferred to the sterile field without contaminating it. The transparent plastic film is shorter than the backing, allowing it to be easily separated from the backing. A row of indentations in the plastic film enhances the security of grasp.

The design of the inner packet for absorbable sutures is different from that of nonabsorbable sutures. Because absorbable sutures must be protected from moisture, the sterile inner packets are hermetically sealed aluminum foil cavities that are designed to be functional tear foil packets. The upper edge of the sterile inner packet has a tear notch that provides consistent easy opening of the foil packet. A TEAR RIGHT indicator is printed on the front of the package to indicate the direction of tearing the foil packet. Tearing the package in the direction of the indicator allows easy access to the needle "parked" in foam that can be armed by right-handed surgeons. Note that each packet has easy to read graphics with the designated expiration date listed for all absorbable suture products.

The inner packet for nonabsorbable sutures has several unique features. It has a mid-peel opening in its packet with an access flap that is lifted from the inner packet and turned 180° to expose the body of the needle whose point and cutting edges are "parked" in foam. By rotating the access flap 180°, the needle is armed by the needle holder from either side of the packet by right- or left-handed surgeons. The needle is positioned in a manner that prevents kinking of the monofilament suture near the swage of the needle.

For either absorbable or nonabsorbable sutures, unique systems have been designed to stabilize the braided and monofilament suture in their packet. For the braided sutures, a retainer of rigid plastic film having a spiral labyrinth is specially designed for delivery of a kink-free suture. The suture exits from the labyrinth in a manner that maintains the suture's straight uniform configuration. The suture is swaged to a needle that is "parked" in foam that protects the delicate needle point and its cutting edges.

The physical and chemical properties of monofilament sutures are distinct from those of braided sutures, causing manufacturers to design a special packing system for monofilament sutures. The plastic memory of the monofilament suture is so great that the shape of the suture conforms to the shape of the packet. Consequently, the monofilament suture is not packaged in a circular configuration, which would cause the suture to assume a coiled configuration. A coiled monofilament suture is an invitation to the knotting of the suture. The monofilament suture is wrapped around four fixation pins in the figure-of-eight shaped loops. The monofilament suture can be straightened to a more linear configuration by apply forces to the suture ends.

References

1. Thacker JG, Rodeheaver G, Kurtz L, Edgerton MT, Edlich RF. Mechanical performance of sutures in surgery. Am J Surg 1977;133:713-715.
2. Trimbos JB. Security of various knots commonly used in surgical practice. Obstet Gynecol 1984;64:274-280.
3. Edlich RF, Wind TC, Hill LG, Thacker JG, McGregor W. Reducing accidental injuries during surgery. J Long Term Eff Implant 2003;13(1):1-10.
4. Edlich RF, Panek PH, Rodeheaver GT, Turnbull VG, Kurtz LD, Edgerton MT. Physical and chemical configuration of sutures in the development of surgical infection. Ann Surg 1973 Jun;177(6):679-688.
5. Postlethwait RW. Long-term comparative study of non-absorbable sutures. Ann Surg 1970;171:892-898.
6. Rodeheaver GT, Nesbit WS, Edlich RF. Novafil, a dynamic suture for wound closure. Ann Surg 1986;204:193-199.
7. Trimbos JB, Smeets M, Verdel M, Hermans J. Cosmetic result of lower midline laparotomy wounds: polybutester and nylon skin suture in a randomized clinical trial. Obstet Gynecol 1993;82(3):390-393.
8. Pinheiro AL, de Castro JF, Thiers FA, Cavalcanti ET, Rego TI, de Quevedo AS, Lins AJ, Aca CR. Using Novafil: would it make suturing easier? Braz Dent J 1997;8(1):21-25.
9. Dang MC, Thacker JG, Hwang JC, Rodeheaver GT, Melton SM, Edlich RF. Some biomechanical considerations of polytetrafluoroethylene sutures. Arch Surg 1990;125(5):647-650.
10. Rodeheaver GT, Shimer AL, Boyd LM, Drake DB, Edlich RF. An innovative absorbable coating for the polybutester suture. J Long-Term Effects Med Implants 2001;11(1 & 2):41-54.
11. Lewis RP, Schweitzer J, Odum BC, Lara WC, Edlich RF, Gampper TJ. Sheets, 3-D strands, trimensinal (3-D) shapes and sutures of either reinforces or nonreinforced expanded polytetrafluoroethylene for facial soft-tissue suspension, augmentation and reconstruction. J Long-Term Effects Med Implant 1998;8:19-42.
12. Towler MA, Tribble CG, Pavlovich LJ, Milam JT, Morgan RF, Edlich RF. Biomechanical performance of new vascular sutures and needles for use in polytetrafluoroethylene grafts. J Appl Biomater 1993;4(1):87-95.
13. Miller CM, Sangiolo P, Jacobson JH II. Reduced anastomotic bleeding using new sutures with a needle-suture diameter ratio of one. Surgery 1987;101(2):156-160.
14. Tera H, Åberg C. Strength of knots in surgery in relation to type of knot, type of suture material and dimension of suture thread. Acta Chir Scand 1977;143(2):75-83.
15. Salthouse TN, Williams JA, Willigan DA. Relationship of cellular enzyme activity to catgut and collagen suture absorption. Surg Gynecol Obstet 1981;129:691-696.
16. Rodeheaver GT, Thacker JG, Edlich RF. Mechanical performance of polyglycolic acid and polyglactin 910 synthetic absorbable sutures. Surg Gynecol Obstet 1981;153:835-841.
17. Faulkner BC, Gear AG, Hellewell TB, Mazzarese PM, Watkins FH, Edlich RF. Biomechanical performance of a braided absorbable suture. Surg Gynecol Obstet 1981;153:497-507.
18. Drake DB, Rodeheaver PE, Edlich RF, Rodeheaver GT. Experimental studies in swine for measurement of suture extrusion. J Long Term Eff Med Implants 2004;14(3):251-259.
19. Storch M, Perry LC, Davidson JM, Ward JJ. A 28-day study of the effect of coated VICRYL™ plus antibiotic suture (coated polyglactin 910 suture with triclosan) on wound healing in guinea pig linear incisional skin wounds. Surg Infect (larchmt). 2002;3 Suppl 1:89-98
20. Rothenburger S, Spangler D, Bhende S, Burkley D. In vitro antimicrobial evaluation of coated VICRL™ plus antibacterial suture (coated polyglactin 910 with triclosan) using zone of inhibition assays. Surg Infect (Larchmt): 2002;3 Suppl 1:79-87
21. Ray JA, Doddi N, Regula D, Williams JA, Melveger A. Polydioxanone (PDS), a novel monofilament synthetic absorbable suture. Surg Gynecol Obstet 1981;153:497-507.
22. Katz AR, Mukherjee DP, Kaganov AL, Gordon S. A new synthetic monofilament absorbable suture made from polytrimethylene carbonate. Surg Gynecol Obstet 1985;161:213-222.
23. Rodeheaver GT, Beltran KA, Green CW, Faulkner BC, Stiles BM, Stanimir GW, Traeland H, Fried GM, Brown HC, Edlich RF. Biomechanical and clinical performance of a new synthetic monofilament suture. J Long-Term Effects Med Implants 1996;6:181- 196.
24. Pineros-Fernandez A, Drake DB, Rodeheaver PA, Moody DL, Edlich RF Rodeheaver GT. CAPROSYN™, another major advance in synthetic monofilament absorbable suture. J Long Term Eff Med Implants 2005;14(5):359-368.
25. Edlich RF, Tsung MS, Rogers W, Rogers P, Wangensteen OH. Studies in the management of the contaminated wound: I. Techniques of closure of such wounds together with a note on a reproducible model. J Surg Res 1968;8:585-592.
26. Edlich RF, Panek PH, Rodeheaver GT, Turnbull VG, Kurtz LD, Edgerton MT. Physical and chemical configuration of sutures in the development of surgical infection. Ann Surg 1973;177:679-688.
27. Sharp WV, Belden TA, King PH, Teague PC. Suture resistance to infection. Surgery 1982;91:61-63.
28. deHoll D, Rodeheaver G, Edgerton MT, Edlich RF. Potentiation of infection of suture closure of dead space. Am J Surg 1974;127:716-720.
29. Foster GE, Hardy EG, Hardcastle JD. Subcuticular suturing after appendectomy. Lancet 1977; 1:1128-1129.
30. Hopkinson GB, Bullen BR. Removable subcuticular skin suture in acute appendicitis: a prospective comparative clinical trial. BMJ (London) 1982;284:869.
31. Polglase A, Nayman J. A comparison of the incidence of wound infection following the use of percutaneous and subcuticular suture: an experimental study. Aust N Z J Surg 1977;47:423-425.
32. Pham S, Rodeheaver GT, Dang MC, Foresman PA, Hwang JC, Edlich RF. Ease of continuous dermal suture removal. J Emerg Med 1990;8:539-543.
33. Winn HR, Jane JA, Rodeheaver G, Edgerton MT, Edlich RF. Influence of subcuticular sutures on scar formation. Am J Surg 1977;133:257-259.
34. Nordström REA, Nordström RM. Absorbable versus nonabsorbable sutures to prevent postoperative stretching of wound areas. Plast Reconstr Surg 1986;78:186-190.
35. McGuire MF. Studies of the excisional wound: I. Biomechanical effects of undermining and wound orientation on closing tension and work. Plast Reconstr Surg 1980;66:419-427.
36. Thacker JG, Rodeheaver GT, Moore JW, Kauzlarich JJ, Kurtz L, Edgerton MT, Edlich RF. Mechanical performance of surgical sutures. Am J Surg 1975;130:374-380.
37. Edlich RF, Rodeheaver GT, Thacker JG. The evaluation of wounds in the emergency department. In Emergency Medicine: A Comprehensive Study Guide, Second Edition, (eds.) Tintinalli JE, Krome RL, Ruiz E, McGraw-Hill Book Co., 1987, p. 929-932.
38. Taylor FW. Surgical knots. Ann Surg 1938;107:458-468.
39. Tera H, Åberg C. Tensile strength of twelve types of knot employed in surgery, using different suture materials. Acta Chir Scand 1976;142:1-7.
40. Rodeheaver GT, Borzelleca DC, Thacker JG, Edlich RF. Unique performance characteristics of Novafil®. Surg Gynecol Obstet 1987;142:230-360.
41. Zimmer CA, Thacker JG, Powell DM, Bellian KT, Becker DG, Rodeheaver GT, Edlich RF. Influence of knot configuration and tying technique on the mechanical performance of sutures. J Emerg Med 1991;9:107-113.
42. Howes EL, Harvey SC. The strength of the healing wound in relation to the holding strength of the catgut suture. N Engl J Med 1929; 200:1285-1290.
43. Holmlund DE. Knot properties of surgical suture materials. A model study. Acta Chir Scand 1974;140:355-362.
44. Tera H, Åberg C. Strength of knots in surgery in relation to type of knot, type of suture material and dimension of suture thread.Acta Chir Scand. 1977;143(2):75-83.
45. Åberg C. Change in strength of aponeurotic tissue enclosed in the suture during the initial healing period. An experimental investigation in rabbits. Acta Chir Scand 1976;142:429-432.
46. Nichols WK, Stanton M, Silver D, Keitzer WF. Anastomotic aneurysms following lower extremity revascularization. Surgery 1980;88:366-374.
47. Stamp CV, McGregor W, Rodeheaver GT, Thacker JG, Towler MA, Edlich RF. Surgical needle holder damage to sutures. Am Surg 1988;54:300-306.
48. Abidin MR, Towler MA, Thacker JG, Nochimson GD, McGregor W, Edlich RF. New attraumatic rounded-edge surgical needle holder jaws. Am J Surg 1989;157:241- 242.
49. Dobrin PB. Surgical manipulation and the tensile strength of polypropylene sutures. Arch Surg 1989;124:665-668.
50. Edlich RF, Thacker JG, McGregor W, Rodeheaver GT. Past, present and future for surgical needles and needle holders. Ann J Surg 1993;166:522-532.
51. Watkins FH, London SD, Neal JG, Thacker JG, Edlich RF. Biomechanical performance of cutting edge surgical needles. J Emerg Med 1997;15:679-685.
52. Ahn LC, Towler MA, McGregor W, Thacker JG, Morgan RF, Edlich RF. Biomechanical performance of laser-drilled and channel taper point needles. J Emerg Med 1992;10:601-606.
53. Thacker JG, Borzelleca DC, Hunter JC, McGregor W, Rodeheaver GT, Edlich RF. Biomechanical analysis of needle holding security. J Biomed Mat Res 1986;20:903-917.
54. Abidin MR, Becker DG, Paley RD, Doctor A, Westwater JJ, McGregor W, Edlich RF. A new compound curved needle for intradermal suture closure. J Emerg Med 1989;7:441-444.
55. Bond RF, McGregor W, Cutler PV, Becker DG, Thacker JG, Edlich RF. Influence of needle holder jaw configuration on the biomechanics of curved surgical needle bending. J Appl Biomat Res 1990;1:39-47.
56. Thacker JG, Borzelleca DC, Hunter JC, McGregor W, Rodeheaver GT, Edlich RF. Biomechanical analysis of needle holding security. J Biomat Res 1986;20:903-917.
57. Abidin MR, Dunlapp JA, Towler MA, Becker DG, Thacker JG, McGregor W, Edlich RF. Metallurgically bonded needle holder jaws. A technique to enhance needle holding security without sutural damage. Am Surg 1990;56:643-647.
58. Noriega LK, Rodeheaver GT, Thacker JG, Edlich RF. Modern concepts of packaging surgical needles and suture. Med Prog Tech 1994; 20:271-279.