Scientific basis for selecting staple and tape skin closures

Use of tape and skin staples has many important clinical applications for surgical wounds. During the past two decades, our research program has identified the optimal performance parameters of these wound closure devices. On the basis of their unique performance characteristics, specific staplers and tapes are recommended for wound closure. The scientific basis for selecting staples and tapes for wound closure is based on their influences on the biology of wound repair and infection.

Scientific basis for selecting surgical needles and needle holders for wound closure

Standardized reproducible tests have been devised to determine surgical needle sharpness, resistance to bending, and ductility. Three comparable groups of reverse cutting edge needles were selected from different manufacturers for measurement of these needle performance parameters. This testing demonstrated that needle diameter, manufacturing process, needle material composition, cross-sectional design, and the manufacturer were all important determinants of surgical needle performance. In addition, the biomechanics of curved surgical needle bending has been related to the clamping moment of surgical needle holders. This relationship identifies the surgical needle holder that can be used with surgical needles without deformation. The results of these studies provide a scientific basis for the selection of surgical needles and needle holders for use in surgery.

Some biomechanical considerations of polytetrafluoroethylene sutures

The biomechanical performance of polytetrafluoroethylene (PTFE) sutures has been compared with that of polypropylene sutures, the standard to which other sutures used in vascular and cardiac surgery are compared. The PTFE is supple and has no plastic memory, while the polypropylene suture is stiff and retains its plastic memory. In addition, the rate of creep encountered in the PTFE suture was significantly less than that of the polypropylene suture. The knotting profiles for knot security for either a square, granny, or surgeon's knot for polypropylene sutures were three throws each. In contrast, knot security with either a square or granny PTFE knot was accomplished with seven throws; six throws were needed for a secure surgeon's knot. The breaking strength of the unknotted and knotted PTFE sutures was approximately one half as great as that for the unknotted and knotted polypropylene sutures. Knot construction significantly reduced the breaking strength of polypropylene sutures but did not alter the breaking strength of PTFE sutures. The percent elongation experienced by both sutures before breakage did not differ significantly. The elasticity, as measured by work recovery, for the polypropylene suture was greater than that for the PTFE suture. On the basis of its unique biomechanical performance characteristics, the PTFE suture should have an important place in vascular and cardiac surgery.

Needle holder damage to surgical needles

Clamping surgical needles between the jaws of needle holders with teeth markedly weaken the needles, making them prone to breakage. In contrast, clamping surgical needles between either smooth needle holder jaws or jaws embedded with tungsten carbide particles did not alter the ductility of surgical needles.

Emergency physician's needle holder

A new needle holder is described that has jaws metallurgically bonded with tungsten carbide particles that enhance needle holding security without causing sutural damage during instrument ties. Scissors have also been incorporated into the needle holder to cut sutures. One ringlet on a handle has been offset to facilitate retrieval of the needle holder from a flat surface.

Biomechanics of curved surgical needle bending

Because needle bending resistance is such an important factor in the selection of surgical needles, a standard quantitative test of needle bending has been devised to study the biomechanics of deformation of needles from three different commercial manufacturers. The superior resistance to deformation of needles made by one manufacturer has been related to the specific alloy, ASTM 45500 stainless steel, employed in its production. The needles produced from ASTM stainless steel 45500 have stronger tensile and yield strengths than those of the other alloys, accounting for their greater resistance to bending.

Surgical needle sharpness

We developed a standard reproducible test to determine surgical needle sharpness. This parameter was measured by recording the maximum force required to push a curved surgical needle through a thin laminated synthetic membrane. Three comparable groups of reversed cutting-edge needles were selected from different manufacturers for needle penetration testing. The results of this testing demonstrated that the needle diameter, manufacturing process, and the manufacturer were all important determinants of needle sharpness. Needles with a smaller diameter were sharper than those with a larger diameter. In addition, electrohoned or hand-honed needles were sharper than those subjected to only machine grinding. When comparably sized needles were compared, Ethicon manufactured the sharpest needles, followed by Davis & Geck and Deknatel needles. Scanning electron microscopic photographs and elemental analysis of the surgical needles could be correlated with their sharpness. The sharper needles had long, narrow cutting edge geometries compared with the short wide geometries of duller needles. The sharpest needles were fabricated from an American Society for Testing and Materials (ASTM) 45500 stainless steel alloy that has stronger tensile and yield strengths than those of ASTM 42000 and 42020 alloys used in the creation of the other needles. This stronger alloy allows the manufacturer to produce a longer, narrower cutting point geometry with reduced danger of either bending or breakage during surgery compared with needles made from weaker alloys (ASTM 42000 and ASTM 42020), which accounts for the superior sharpness of the Ethicon surgical needles.

New atraumatic rounded-edge surgical needle holder jaws

A new atraumatic smooth needle holder jaw with rounded edges that does not damage synthetic monofilament sutures is described herein. These rounded edges were created by mechanical filing of the sharp edges of smooth needle jaws. Compression of the monofilament suture between the needle holder jaw with sharp edges reduces the suture breaking strength compared with that of control sutures. A quality control method has been devised to detect the potentially damaging sharp edges of smooth needle jaws that can be easily implemented by needle holder manufacturers.

A new quantitative measurement for surgical needle ductility

Because surgical needle ductility is such an important factor in the selection of surgical needles, a new curved needle ductility test instrument was devised to measure the ductility of needles from three commercial manufacturers. The superior ductility of needles made by one manufacturer was related to the specific alloy, stainless steel ASTM 45500, used in their production. The ASTM 45500 stainless steel has a significantly greater tensile and yield strength than the other stainless steel alloys, accounting for its superior ductility.

Principles of emergency wound management

Every traumatic wound treated in the emergency department is a result of a finite energy source that caused tissue disruption. The dynamics of this exchange of energy will determine the magnitude of injury. Disruption of the body covering leaves the once-sterile underlying integument exposed to contamination. The contaminants are derived from either the victim (endogenous) or the exogenous energy source. The presence of a contaminant such as bacteria makes the care of the wound an exercise in microbiology. Other contaminants, such as dirt, also may reside in the recesses of the wound. Emergency physicians must understand the consequences of tissue trauma. A study of the mechanism of injury will provide a reliable indication of damages. Whether the tissue injury will be limited to the initial wounding depends on the outcome of the interaction between the contaminants and the wound. In the event that the contaminants are very reactive, a relatively insignificant wound may become a catastrophe. This circumstance can be averted by the implementation of a well-devised plan based on the biology of wound healing and infection.

Influence of cutting edge configuration on surgical needle penetration forces

A standardized test for measuring the needle penetration forces has been developed that can be easily replicated in any laboratory. Using this test, conventional cutting edge needles utilized in the test produced lower penetration forces than reverse cutting edge needles. The lower penetration forces encountered by the conventional cutting edge needles imply that the physician should be able to handle these needles with more dexterity and precision than the reverse cutting edge needle.

Evaluation of automatic disposable rotating cartridge skin staplers

Burn surgeons commonly employ skin staples for the application of skin grafts and to secure dressings on donor site dressings and over skin grafts. Disposable skin staplers with rotating cartridges are ideally suited for wound closure because the position of their cartridges can be manually adjusted to facilitate placement of their staples. In response to the burgeoning interest in disposable automatic skin staplers with rotating cartridges, three different models are now commercially available. This report describes the design configuration and mechanical performance of these disposable automatic staplers and their staples. Mechanical performance of these staplers and staples has been assessed by standardized tests that can be replicated in any research laboratory. On the basis of these objective design and performance parameters, the Premium stapler is recommended for wound closure. This stapler provides maximal visualization of the wound as well as the staple during its formation. It delivers the staple into the skin or wound in a manner that the cross member of the staple is above the skin or wound surface. In addition, the Premium stapler has a prepositioning mechanism that can be controlled by the surgeon with minimal force. This mechanism allows the stapler to hold its staple securely, even when its pointed legs extend beyond the delivery end of the stapler. Force required to form its staples is so low that the surgeon can staple repetitively without fatigue. Finally, the Premium stapler delivers a staple that has a uniform geometry and sharp points that can easily penetrate tissue.

Splayed handle surgical scissors

Splayed handle surgical scissors have distinct advantages over conventional scissors that limit hand fatigability. The ringlet configuration of the splayed scissors conforms to the normal resting posture of the hand. In addition, surgeons can apply greater force to the splayed scissor ringlets than that which could be applied to the ringlets of conventional scissors.

A new hydrofitness device for strengthening muscles of the upper extremity

A new hydrofitness device has been devised for strengthening upper extremity muscles during aquatic exercise. It consists of a molded plastic fenestrated outer shell with an inner rotating disc that can be easily adjusted to alter the surface area of its frontal presentation. By changing the surface area of its frontal presentation a graded, individualized exercise program can be prescribed. A buoyant foam disc has been incorporated into the device to prevent it from sinking to the bottom of the pool. On the basis of this evaluation, performance of this device was judged to be superior to that of other devices for strengthening upper extremity muscles during aquatic exercise.

Automatic wire twister

This automatic wire twister used in surgery consists of a 6-inch needle holder attached to a twisting mechanism. The major advantage of this device is that it twists wires significantly more rapidly than the conventional manual techniques. Testing has found that the ultimate force required to disrupt the wires twisted by either the automatic wire twister or manual techniques did not differ significantly and was directly related to the number of twists. The automatic wire twister reduces the time needed for wire twisting without altering the security of the twisted wire.

Surgical needle holder damage to sutures

Needle holder jaws with teeth produce distinct structural changes in synthetic sutures that cause a marked reduction in the suture breaking strength. This damage to the suture may account for disruptions of vascular and fascial wound closures in which continuous closure techniques are employed.

Hydrofitness devices for strengthening upper extremity muscles

Our evaluation of hydrofitness devices for strengthening arm muscles has revealed several important determinants of their performance. Most importantly, the device's frontal projection should be in the shape of a paddle whose surface area can be varied to meet the individual exerciser's needs. Its weight should be light to minimize the inertial forces encountered in charging the velocity of paddle movement. Its handle should have a relatively large circumference without digital profiling. These optimal performance parameters have been recently incorporated into a new hydrofitness device that will be commercially available for aquatic exercise programs for strengthening upper extremity muscles.

Mechanical performance of monofilament synthetic absorbable sutures

The purpose of this study was to evaluate the mechanical performance of two new synthetic monofilament absorbable sutures. The polydioxanone sutures is prepared by polymerizing and extruding the monomer, paradioxanone, in the presence of a suitable catalyst. The other suture is a modified polyglycolic acid suture, made by reacting trimethylene carbonate and glycolide. The knot configuration (1 = 1 = 1, 1 x 1 x 1, and 2 = 1 = 1) required for knot security was identical for the two synthetic monofilament sutures. The mean knot breaking strengths for the polydioxanone and modified polyglycolic acid sutures did not differ significantly. The surfaces of these sutures exhibited a low coefficient of friction which was slightly increased by hydration. The most distinctive difference between the handling characteristics of these two sutures was their flexural rigidity. The stiffness of the polydioxanone suture was 60 percent greater than that of the modified polyglycolic acid suture.

Bioengineering principles of hydrotherapy

Hydrotherapy is based on several important bioengineering principles that permit the design and development of aquatic exercise devices, techniques and programs. These principles involve several forces (buoyancy, drag, inertia), hydrostatic pressure and the specific heat of water. By acquiring a knowledge of these bioengineering principles, an individualized exercise program can be prescribed that will enhance physical fitness which is associated with desirable psychological changes.

Mechanical performance of exertubing for isotonic hand exercise

The purpose of this study was to determine the mechanical performance of hollow latex rubber tubes used for hand rehabilitation. The results of this investigation provide load extension profiles of each tube that document the forces required to elongate the tube to a specific length. By relating these mechanical performance tests to quantitative measures of hand strength, an individualized exercise prescription can be designed for rehabilitation of the injured hand.

Considerations in the choice of sutures for wound closure of the genitourinary tract

The ideal suture for use within the urinary tract should maintain its tensile strength until wound repair is satisfactory and then it should undergo rapid total absorption without promoting stone formation. The bladder has a great potential for repair, attaining 100 per cent of the strength of the unwounded tissue in 14 to 21 days. Braided synthetic absorbable sutures appear to be suited ideally for closure of incised wounds of a urinary conduit. They maintain their tensile strength for approximately 21 days, during which time the healing tissues regain strength rapidly. Because sutures are foreign bodies and have access to urine, they may serve as a nidus for stone formation. Several factors that have been identified as important determinants of foreign body urolithiasis include the presence of urine, urine volume and pH, infection, physical and chemical configuration of the foreign body, and animal species. The incidence of suture urolithiasis is related directly to the duration in which the sutures are present in the urinary tract. Consequently, absorbable sutures are preferred over nonabsorbable sutures for closure of wounds of the urinary conduit. In the absence of infection braided synthetic absorbable sutures have distinct advantages over gut sutures for closure of urinary tract wounds. They are absorbed by nonenzymatic hydrolysis in a predictable manner with limited inflammatory response. In contrast, gut sutures have an unpredictable absorption rate by enzymatic degradation and elicit an exaggerated inflammatory response. Because infected urine, especially Proteus species, accelerates the degradation of absorbable synthetic sutures to a greater degree than gut sutures, wound closure in the presence of infection should be accomplished with the absorbable natural fiber suture. Nonabsorbable sutures or staples should not be used in the urinary tract because they predictably promote urolithiasis.

Unique performance characteristics of Novafil

Polybutester is a unique copolymer that can be extruded as a flexible monofilament nonabsorbable suture. The mechanical performance of this new suture material was compared with that of polypropylene and nylon. The results indicate that polybutester sutures are as strong, have the same degree of total elongation at break and knot as the other monofilament sutures. In contrast with polypropylene and nylon sutures, the polybutester sutures have a perceptible stretch, are more elastic and flexible, and exhibit less creep. Polybutester sutures appear to be an acceptable alternative to polypropylene and nylon sutures and their unique mechanical properties may even prove to be superior in vivo.

Performance of disposable needle syringe systems for local anesthesia

The performance of different disposable needle syringe systems was determined by measuring needle-puncture pain, needle-bending forces, and the fluid dynamics of the systems. Thirty-gauge needles cause less needle-puncture pain than any other needle. The force required to bend the 30-gauge needle irreversibly was lower than that for the other needles. Studies of the fluid dynamics of different needle syringe assemblies demonstrated that the flow rate can be limited by using large-size syringes (30 mL) and needles with the smallest internal diameter. On the basis of the results of this study, 30-gauge needles attached to 10-mL syringes are recommended for infiltration anesthesia, and 25-gauge needles with 10-mL syringes are advocated for regional nerve blocks. In infiltration anesthesia, the local anesthetic agent should be injected slowly into the subdermal tissue over a 10-second period. When performing regional nerve blocks, it is also advisable to inject the local anesthetic agent over a 10-second time interval.

Mechanical performance of a work hardened pointed surgical wire

The design and material properties of a surgical wire have been enhanced to improve its performance in surgery. One blunt end of the wire has been honed to a point to decrease the axial compressive force required to penetrate tissue. In addition, its sharp end has been work hardened to increase its yield strength. The mechanical performance of this wire has been characterized by a series of in vitro experiments and a clinical trial.

Heat welding for surgical sutures

The purpose of this experimental study was to test the potential value of heat welding to cut the ends of knotted surgical sutures. This heat process resulted in knot security in a coated polyglactin suture with fewer throws than those needed for the same suture with knotted ends cut by scissors. Results of mechanical performance testing of the knotted sutures cut either by scissors or welding did not differ significantly. With refinements in the technical design of the heat source, suture welding may have important applications in surgery.

Wheelchair tire rolling resistance and fatigue

The hysteresis loss theory of rolling resistance is developed for solid rubber wheelchair tires. The analysis is used to correlate test data for a clay-filled natural rubber and a polyurethane tire material. A discussion of tire rolling work, hysteresis loss factor measurement, and rolling loss measurement is presented. An example calculation of rolling resistance for a polyurethane tire is given in detail. The subject of solid rubber tire design is developed on the basis of recommended fatigue life theory and practice. It is shown that polyurethane tires have a useful fatigue life due to a high shear modulus at useful values of hardness. This characteristic of polyurethane, if exploited, is predicted to lead to a tire with a lower rolling resistance than other wheelchair tires available. The effect of surface roughness on rolling resistance is briefly discussed and some experimental results are listed. The purpose of this paper is to give the rehabilitation engineer the means for wheelchair tire rolling resistance and fatigue life design and the methods to assess the tire characteristics when a tire design is modified or a new tire material is contemplated. Other important design factors, such as wear and chemical degradation, are not discussed, but references are suggested for information on these topics. As in most research and development projects, this study raises problems which need further work. For example, the fatigue properties of the rubber compounds employed in this application are not completely understood; this subject is planned for future investigation.

Evaluation of a new, improved surgical drainage system

A new, improved drainage system has been specifically designed to provide either closed suction drainage for the ambulating patient or sump drainage for the patient confined to bed. This drainage system is made of silicone that has a hydrogel coating with a low coefficient of friction. This coating facilitates removal of the drain from the wound cavity and reduces the adherence of blood clots in the drainage system. A filter assembly is attached to the air vent lumen to remove particulate matter and bacteria from the air. Clinical evaluation of the filtered sump drainage system has confirmed its superiority over closed suction in its efficiency of removing fluids from the wound.

Wheelchair caster shimmy and turning resistance

The equations for wheelchair caster wheel shimmy are presented along with experimental data. The report includes the theory and performance of single wheel casters for a variety of tires, and a new design for wheelchair casters using a grooved dual-tread tire or co-rotating caster wheels. The dual-tread tire was found to significantly inhibit caster shimmy. The turning resistance due to a grooved caster wheel tire with a 1/2-inch groove was found to be 10 percent greater than for an ungrooved caster wheel tire. The analysis includes the methodology and the results of experiments developed to measure the sliding friction turning moment of the wheelchair caster wheel. A number of commercial wheelchair caster wheels were tested and the results for shimmy are presented.

Knotting and handling characteristics of coated synthetic absorbable sutures

The purpose of this study was to evaluate the knotting and handling characteristics of the new coated synthetic absorbable sutures. When compared to the coated polyglactin 910 sutures, the coated polyglycolic acid sutures displayed a lower coefficient of friction, encountered less tissue drag forces, and exhibited less flexural rigidity. In the case of sizes O, 2-O, and 3-O coated polyglycolic sutures, knot security was achieved with one less throw than with similar sizes of coated polyglactin 910 sutures. On the basis of these comprehensive mechanical performance tests, the knotting and handling characteristics of the coated polyglycolic acid sutures were judged to be superior to that of the coated polyglactin 910 sutures.

Rehabilitation engineering education at the University of Virginia

The graduate rehabilitation engineering program of study at the University of Virginia is the first program of its type in the United States. The first students were admitted to the program in the fall of 1979. The program is designed to train students with engineering and clinical science backgrounds in the field of rehabilitation engineering. Emphasis is placed on practical training through internship activities at the University of Virginia Rehabilitation Engineering Center and Medical School Department of Orthopedics and Rehabilitation. Field experience is received at the Woodrow Wilson Rehabilitation Center and the University of Virginia Children's Rehabilitation Center.

Mechanical performance of polyglycolic acid and polyglactin 910 synthetic absorbable sutures

The mechanical performance of polyglycolic acid and polyglactin 910 sutures has been assessed using standardized reproducible tests. The results of these studies demonstrated distinct differences in their performance that can be related, in part, to their structural configuration. The size of the 4-0 polyglactin suture was significantly larger than that of the 4-0 polyglycolic acid suture. Since the strength of any suture is proportional to its cross sectional area, the strength of unknotted and knotted polyglactin 910 sutures was signficantly greater than that of the polyglycolic acid sutures. The strength of both sutures was similarly diminished by the formation of the knot. When these sutures were added to tissue, the breaking strength was even further reduced. The rate of decline in breaking strength of the two absorbable sutures in healing skin wounds was comparable. These absorbable sutures displayed knot security with a two throw square knot, 1 = 1. The ability of these sutures to reach knot break with this knot configuration is characteristic of sutures in which the surface exhibits a high coefficient of friction. Their rough surface also caused them to drag through tissue, making difficult to adjust tension on a continuous running suture.

Moiré interferometry strain measurements in elastic thin membranes

The strain in thin flexible membranes representing human skin has been studied using moiré interferometry. A method of using a flexible coating of photographic emulsion was developed. The equations for use in differential interferometry were also derived for very large deformations. The method was applied to two types of cases: rectangular membranes subjected to a uniform axial strain, and membranes containing strain concentrators that represent bandages placed on the surface of the skin. Results for the former case were within 3% of exact results, while results near the concentrator indicate strain concentration factors ranging from -1.25 to 1.75.

Finite deformation theory for in vivo human skin

A finite deformation mathematical model of in vivo human skin has been developed for the normal physiological load range. Uniaxial load-deformation measurements were carried out with a non-invasive extensometer and utilized in formulating the model. The in vivo strain energy function was found to be a linear function of the first two strain invariants and a quadratic function of the third strain invariant. Only three independent constants were necessary to specify the strain energy function completely for the upper extremities of human volunteers.

Mechanical performance of sutures in surgery

In this study, we have compared the recommended configuration of a knot with specified sutures as ascertained by mechanical performance tests to that employed by a group of board-certified surgeons. Agreement between the surgeon and the results of the test was encountered in only one fourth of the instances. In another one fourth of the cases the surgeon overestimated the number of throws required for a knot to reach knot break. This additional suture material further handicaps the host's defenses, thereby inviting infection. Surgeons employed knots that untied without reaching knot break in the remaining half of the cases. The holding power of many of the knots that untied was substantially less than that of knots reaching knot break. On the basis of the study, it is recommended that results of the mechanical performance tests be made readily available to the surgeon so that his patient can receive maximal benefits from the knotted suture with the least damage to the host's defenses.

Practical applications of skin biomechanics

The biomechanical properties of skin have an important influence on plastic surgical decisions. They aid the surgeon in planning elective incisions, excisions, or scar revisions. They provide insight into the most appropriate method of coverage of skin defects as well as the design of an artificial skin substitute. Skin biomechanics can, in part, be characterized in vivo by either a skin extensiometer or by studying the deformation of skin defects. These methods indicate the magnitude and directional orientation of skin tensions which are dependent partly on the mechanical characteristics of the dermal fibers and partly on the pattern in which they are woven. The tensions to which the skin are subjected can be classified as either static or dynamic in origin. Static skin tensions are the natural tensions existing in skin. The magnitude of static tensions varies between individuals, at different sites in the same person, and in different directions in many sites. The dynamic tensions are caused by a combination of forces which are associated with joint movement, mimetic and other voluntary muscle activity, and gravity. Knowledge of these tensions allows the surgeon to align the operative site in the direction of maximal tension and to approximate the wound with the least amount of tension. As a consequence of this, the scar healing between the cut edges of the wound should be narrow and inconspicuous.

Management of soft tissue injury

The fate of a surgical wound is held in a delicate balance between the host's resistance to infection and the causal factors of infection. Considerable insight into this relationship between the host and pathogen can be gained from the results of quantitative bacteriologic measurements. Newer rapid slide techniques have been developed which provide the surgeon with this information within 20 minutes. In most soft tissue injuries, the wound bacterial count gives an accurate prediction of subsequent infection. Wounds combining greater than 10(5) bacteria per gram of tissue are destined to develop infection. When the bacterial count is below that level, the wounds will usually heal per primam without infection. This large number of bacteria required to elicit infection reflects the remarkable ability of soft tissues to resist infection. This state of high resistance to infection can be reduced by several factors which include circulatory embarrassment, tissue injury, dead space, and the presence of foreign bodies (dirt, sutures, drains, etc.). When treating soft tissue injuries, the surgeon must employ specific therapeutic modalities that allow the wound to heal per primam without infection. On the basis of experimental studies supported by clinical experience, the following treatment protocol for soft tissue injuries is recommended. Using strict aseptic technique, the wound must be first anesthetized with 1 per cent Xylocaine to permit painless sound cleansing. All wounds should be subjected to high pressure syringe irrigation to remove bacteria, foreign bodies, and blood clots. When necessary, debridement of all devitalized tissue should be performed with a stainless steel scalpel. Many wounds caused by sharp wounding agents contain no foreign bodies and few bacteria and exhibit considerable resistance to infection. In these wounds, primary closure can be initiated after irrigation without the development of infection. Wounds resulting from impact forces have a diminished resistance to infection and are susceptible to infection by low level of bacterial contamination. Immediate antibiotic treatment of patients with impact injuries subjected to meticulous debridement and cleansing will permit a safe primary closure. In wounds contacted by pus or feces, open wound management followed by delayed primary closure is usually indicated. Antimicrobial prophylaxis is also recommended for patients with such wounds. Ideal postoperative care of all traumatic wounds includes a surgical dressing and immobilization and elevation of the site of injury.

Side-effects of high pressure irrigation

This study was undertaken to identify side-effects of high pressure irrigation. Standardized surgical wounds made in Yorkshire pigs were subjected to high pressure syringe and pulsatile irrigation. As a result of these treatments, fluids were disseminated into the adjacent tissue of the wound, predominantly in a lateral direction. Bacteria did not accompany this disseminated fluid and apparently were filtered out by the surface tissues. This treatment results in a tissue injury which impairs its defenses, making the wound more susceptible to infection. However, the remarkable cleansing capacity of high pressure irrigation appears to outweigh this side-effect, since heavily contaminated wounds subjected to this treatment heal per primum without infection.

Cleansing the traumatic wound by high pressure syringe irrigation

The purpose of this study was to examine the influence of the fluid dynamics of syringe irrigation on the efficacy of wound cleansing and the infection rate of experimental wounds. The pressure experienced by a surface following wound irrigation was directly proportional to the pressure within the syringe and the size of the needle. High pressure syringe irrigation effectively removed bacteria from the surface of the wound. This reduction in the wound bacterial count resulted in a decrease in the infection rate of tissues. Low pressure irrigation with an asepto syringe did not significantly cleanse the wound of its bacterial contaminants and had no demonstrable clinical merit. On the basis of these studies, high pressure syringe irrigation is being employed routinely in our emergency department for the care of traumatic wounds.

Mechanical performance of surgical sutures

A comprehensive analysis of the mechanical performance of sutures has been made to provide information concerning the reliability and security of knotted sutures. The tests utilized in this analysis were designed to be easily reproduced by other investigators. The construction of the knot and the knot performance analysis were undertaken utilizing an Instron Tensile Tester. The mechanical reliability of each knotted suture was determined by measuring the number of throws to reach knot break, the expected slippage of the knot when it reaches knot break, and the maximal holding force at knot break. On the basis of these measurements, recommendations are made for the use of a suture at operation.

Wound cleansing by high pressure irrigation

All traumatic wounds are contaminated to some degree by both soil and bacteria. Specific infection potentiating factors in soil impair the defenses of the tissue and invite infection. These factors are small in size and resist removal by low pressure irrigation. The efficiency of wound irrigation is markedly improved by delivering the irrigant to the wound under continuous high pressure. Irrigation of the wound with saline solution delivered at 15 pounds per square inch removed 84.8 per cent of the soil infection potentiating factors from the wound. The residual infection potentiating factors remaining in the wound did not significantly impair tissue defenses. On the basis of these experimental studies, clinical studies are now being initiated to test the therapeutic value of high pressure irrigation in traumatic wounds in humans.

Mechanical cleansing of contaminated wounds with a surfactant

Mechanical cleansing of a wound with a sponge soaked in a surfactant has prevented the development of experimental wound infection. The surfactant utilized for wound cleansing is Pluronic F-68, a member of a family of block copolymers called Pluronic polyols. Long-term toxicity studies and clinical trials suggest that this surfactant is safe for human use. Pluronic F-68 is a nonionic detergent that does not have any intrinsic antibacterial activity. Although mechanical cleansing with saline-soaked sponges effectively removes bacteria, it damages the wound and impairs its resistance to infection. The severity of the damage to the skin exerted by the sponge can be correlated with its porosity. Sponges with a low porosity are abrasive and exert more damage to skin than do sponges with a higher porosity. The addition of Pluronic F-68 to even the most abrasive sponges ensures that the bacterial removal efficiency of the sponge scrub is maintained, while tissue trauma is minimized. This dual effect of the surfactant results in a dramatic reduction in the infection rate of contaminated wounds. On the basis of these results, a clinical trial with surfactant-soaked sponges would appear to be indicated.