Incision Characteristics Associated With Six Laparoscopic Trocar-Cannula Systems: A Randomized, Observer-Blinded Comparison CHRISTOPHER M. TARNAY, MD, KAREN B. GLASS, MD, AND MALCOLM G. MUNRO, MD Objective: Laparoscopic trocar-cannula systems of different design but similar internal diameter result in incisions of varying dimensions. Such variations might affect the incidence of incisional complications, such as dehiscence and hernia. We developed a system to measure associated fascial defects and then used the techniques to compare the defects resulting from different trocar-cannula systems. Methods: This was a randomized, observer-blinded study. Six laparoscopic trocar-cannula systems of similar diameter (12 mm) were tested (two pyramidal, two blunt conical, and two cutting-dilating) using a white swine model. All systems were inserted into each of 12 subjects, with location designated by random allotment (total 72 insertions). The fascial defects were exposed and then directly measured for incisional length and area by an observer blinded to the system used. Means of each outcome variable (incisional length and area) were compared using factorial analysis of variance. Results: The values for mean incisional areas were as follows: cutting-dilating 28.73 mm2 and 31.09 mm2, pyramidal 18.25 mm2 and 26.75 mm2, and blunt conical 10.00 mm2 and 12.33 mm2. Mean maximal incisional lengths were similar among all trocar-cannula systems. Conclusion: Blunt conical trocar-cannula systems resulted in significantly smaller fascial defects compared with the widely used pyramidal and the two cutting-dilating trocarcannula systems tested. These differences have potential clinical implications. For example, smaller fascial defects could reduce risk of incisional hernia and dehiscence. (Obstet Gynecol 1999;94:89 –93. © 1999 by The American College of Obstetricians and Gynecologists.)
As minimally invasive surgery becomes more prevalent in surgical treatment, the laparoscope is now an instru-
From the Department of Obstetrics and Gynecology, University of California, Los Angeles, Los Angeles, California. Financial support for this research has been provided by an unrestricted educational grant from ConMed Corporation, Utica, New York.
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ment used by almost all surgical disciplines. With the expanded use of the laparoscope, surgeons are increasingly aware of the nature and frequency of complications secondary to the incisions made for positioning the laparoscopic cannulas or ports. Although originally considered to be rare occurrences, incisional dehiscence and hernia have proved to be more frequent than previously thought.1 This result is perhaps related to both the increasing number and size of cannulas used in contemporary laparoscopic surgery,2,3 as well as the greater number of patients being examined and treated using laparoscopy. The trocar-cannula systems generally have an outer cannula or port and an internal obturator with a narrow or sharp tip, generally referred to as the trocar. There exist a number of other trocar designs, but the most common is a three-sided pyramidal design. Other designs include blunt, conical, and hybrid tips. The differences in design might affect the resultant fascial defect and the subsequent risk of incisional hernia. Fascial dehiscence, the rapid formation of a defect in the rectus fascia, and incisional hernia, the delayed protrusion of peritoneum through a fascial defect, are two different but related complications of laparoscopic trocar-cannula system entry that were rarely reported until the 1990s.2–5 Until this time, the abdominal fascia was generally left open, an approach that in some instances led to dehiscence or postoperative hernia and the subsequent potential for bowel incarceration and obstruction. Retrospective studies suggested that when the fascia was left open, the risk of dehiscence and incisional hernia formation was proportionate to the diameter of the cannula system, at either umbilical or extraumbilical sites.6 Although the exact incidence is unknown, a large survey of gynecologists found over 900 of these complications.1 Existing evidence suggests that incisional hernias are rare in association with the
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Figure 1. The six trocar-cannula system tips. A) ConMed TroGard, blunt conical tip. B) Innerdyne Step, radially expanding blunt conical tip. C) Ethicon Endopath Dilating Tip, blunt dilating tip. D) Dexide System, curvilinear blade with blunt dilating tip. E) Autosuture Surgical Surgiport, pyramidal tip. F) Ethicon Endopath TriStar, pyramidal tip.
use of trocar-cannula systems 8 mm or less in diameter, uncommon when using 10-mm ports, and most common when using systems of 12 mm or more in diameter.2,4,7 As a result of this information, many surgeons have recommended routine closure of fascial incisions produced by trocar-cannula systems with an internal diameter of 10 mm or greater. However, closure of the fascia provides no guarantee that dehiscence or hernia will be prevented. The influence of trocar-cannula system design on incision characteristics has received relatively little attention, probably because of the perception that dehiscence and hernia were unlikely complications. There is anecdotal evidence that conical trocar designs are associated with smaller fascial incisions than those created by pyramidal devices of similar diameter. If this is true, it is possible that trocar-cannula systems with a conical design would be associated with a significantly less incisional dehiscence and hernia, potentially low enough to obviate the need for fascial closure. To address this paucity of information we evaluated the incisions created by various trocar-cannula systems with similar internal diameters but different shapes. It was necessary first to measure the size of the fascial defects resulting from insertion of the trocar-cannula system and then to comparatively evaluate incisions made by the different trocar-cannula systems. Our hypothesis was that the incisional area created by conical trocars would be significantly less than that created by pyramidal trocars.
Materials and Methods Six different disposable laparoscopic trocar-cannula systems were compared, all with an internal diameter of 12 mm, according to the manufacturer (Figure 1). Included were two pyramidal tip designs, the Ethicon Endopath TriStar (Ethicon Endosurgery Inc., Cincin-
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nati, OH) and the Autosuture Surgical Surgiport (United States Surgical Corp., Stamford, CT). Each of these devices has a pyramidal metal cutting blade and an outer sleeve, or obturator, that retracts for insertion and then redeploys upon entry into the peritoneal cavity, thereby covering the sharp trocar tip. The second group of trocar-cannula systems included two blunt conical designs, the ConMed TroGard (ConMed Corp.) and a radially expanding tip, the Innerdyne Step (Innerdyne Inc., Sunnyvale, CA). Neither of these systems has movable metal parts, and both have a blunt plastic trocar. The Innerdyne system is unique in that it requires that a radially expanding sheath be inserted using a standard 15-cm insufflation needle that is subsequently removed. Then the tapered blunt conical trocar, with cannula, is inserted, expanding the sheath and the tract in the abdominal wall. The third group of trocar-cannula systems could be considered hybrids of the first two, containing smaller leading linear blades to create incisions that are then dilated with the aftercoming blunt component of the trocar. Included were the Ethicon Endopath Dilating Tip (Ethicon Endosurgery Inc.), which has a retractable blade housed within a blunt dilating trocar tip, and the Dexide System (Dexide Inc., Ft. Worth, TX), which has a unique curvilinear cutting blade that partially surrounds a retractable blunt-tipped dilating trocar. No additional devices, such as anchoring systems, were affixed to the trocarcannula systems, to eliminate their potential influence on the wound characteristics. Female white swine, each weighing 60 – 65 kg, were selected as test subjects, both because of their size and their dual layer lower abdominal wall fascia that, in our pilot studies, was most representative of human thickness with respect to layers of muscular aponeuroses. The protocols were reviewed and approved by the University of California, Los Angeles Chancellor’s Animal Research Committee, and the animals were cared for in compliance with the University of California, Los Angeles Office for Protection of Research Subjects. Animals were anesthetized with ketamine and butorphanol and maintained with inhaled halothane, titrated to effect. The abdomens were shaved, a Veress needle was placed supraumbilically in the midline, and CO2 gas was insufflated to maintain pressure between 10 and 12 mmHg. A 10-mm trocar-cannula system was inserted subumbilically to allow a laparoscope to be introduced for internal visualization of the experimental trocar-cannula system insertions. In pilot studies we determined that more than six trocar-cannula insertions (in addition to that made for the laparoscope) compromised our ability to maintain adequate intraperitoneal pressure. Consequently, six trocar-cannula systems were inserted by direct vision through one of six
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incision area) were compared using analysis of variance. The analysis of variance is a mixed model analysis of variance with two fixed factors (trocar and location) and one random factor (swine). Pairwise comparisons among the six trocar-cannula system groups were carried out using the Fisher-Tukey (least significant difference) criteria.
Results
Figure 2. Mean area of fascial defect (mm2). A) ConMed TroGard. B) Innerdyne Step. C) Ethicon Endopath Dilating Tip. D) Dexide System. E) Autosuture Surgical Surgiport. F) Ethicon Endopath TriStar.
transverse, 1.8-cm, paramedian incisions that were made in a uniform manner below the level of the umbilicus and separated by 8 to 10 cm. Each trocarcannula system was introduced by the same experienced operator (MGM), at a 45-degree angle to the horizontal, with attention paid to orientation, if indicated by the manufacturer, for a specific trocar-cannula system. Swine were assigned for all possible combinations of trocar and location. The assignment consisted of a Latin square across trocar-cannula and location in a random order.8 At the end of all testing, the animals were euthanized according to institution protocol. This study was done concurrently with another related experiment using the same study population in which force and pressure measurements were obtained during trocar-cannula system introduction. After trocar-cannula system insertions were completed, the instruments were removed. To measure incision length and area, an observer masked to instrument insertions who was experienced in surgery (KBG) measured all wounds. The animals were maintained under anesthesia as the skin and subcutaneous tissues were dissected carefully, exposing the surgical wounds while maintaining their integrity. Maximal length was measured using metric calipers, and wound area was determined by tracing its outline on a transparency grid of 2-mm squares that was placed over the exposed area of the defect. The sum of the grid box quartiles was tabulated and the area calculated in square millimeters. The masked observer also recorded qualitative aspects of the wounds, such as shape and the presence or absence of gross fibromuscular damage, if present. Means of each outcome variable (incision length and
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The defect in the fascia from each trocar-cannula system is expressed as the mean area, as follows: ConMed TroGard 12.33 mm2, Innerdyne Step 10.00 mm2, Ethicon Endopath Dilating Tip 28.73 mm2, Dexide 31.09 mm2, Autosuture Surgiport 18.25 mm2, and Ethicon Endopath Tri-Star 26.75 mm2. Error bars are the standard error of the mean (Figure 2). Incision length is expressed as the mean maximal length of the 12 fascial wounds created by each trocar-cannula system and are as follows: ConMed TroGard 1.41 cm, Innerdyne Step 1.28 cm, Ethicon Endopath Dilating Tip 1.09 cm, Dexide 1.14 cm, Autosuture Surgiport 1.08 cm, and Ethicon Endopath TriStar 1.15 cm. Error bars are the standard error of the mean (Figure 3). The range was 1.06 to 1.40 cm. There were additional, nonquantified, but important, observations related to the structure of the wounds that seemed consistent within groups. For all four devices that incorporated cutting trocars, it was evident that both fascia and muscle fibers were transected. However, when either of the blunt conical devices was used, the muscular and fascial fibers had little gross damage. Instead the fibers were separated from each other in a linear fashion, apparently along natural fibrofascial lines (Figure 4). Statistical analysis demonstrated that only differences in trocar influenced incision length and area. Neither location nor the interaction between trocar and location had an effect on incisional outcomes.
Figure 3. Mean incision length (mm). A) ConMed TroGard. B) Innerdyne Step. C) Ethicon Endopath Dilating Tip. D) Dexide System. E) Autosuture Surgical Surgiport. F) Ethicon Endopath TriStar.
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Figure 4. Photographic and graphic depictions of wounds from pyramidal (top) and blunt conical (bottom) trocar-cannula systems. Note the transection of muscular and fascial fibers that occurs with the pyramidal trocars, which is absent from the wounds associated with the blunt conical systems. Arrows indicate superior wound margin.
Discussion Fascial incisions created by either of the blunt conical trocar-cannula systems (ConMed, Innerdyne) were markedly smaller than those created by the pyramidal and cutting-dilating designs. Conversely, incision lengths were slightly longer when blunt trocars were used, a finding that reached statistical significance only for the ConMed device. Additionally, the narrow range for incision length raises the question of its clinical relevance given the demonstrable differences between trocar-cannula systems in wound area. Our findings and observations allow us to formulate a theory that we believe supports the hypothesis, that incision area has greater potential clinical significance than wound length. First, as noted above, the magnitude of the differences is greater for wound area than incision length. The larger wound area associated with cutting trocars reflects the greater degree of fascial fiber damage imparted by the edge of the blade or pyramidal tip as it traverses the abdominal wall. This damage extends beneath the fascial layer to the abdominal muscle, which further reduces support for the overlying fascia and which contributes to the gaping nature of the wound. The markedly smaller wound area associated with the blunt conical trocar-cannula systems occurred despite the 0.14- to 0.26-cm increase in wound length over the next longest wound length from another trocar-cannula system. These differences seem to reflect the mechanism of entry of the blunt conical devices, which start with a small, pierced, fascial hole that is then dilated until the defect is of sufficient caliber to allow passage of the trocar-cannula system. This dilation results in extension along fascial lines with minimal apparent destruction of tissue. The absence of tearing
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mandates that the incision length be greater than that of the cutting trocars to allow passage of the cannula. Although no objective, direct measurements were made of muscle injury, it was observed that such damage was minimal when blunt conical systems were used, as dilation was the principal mechanism of entry. Furthermore, after removal of the trocar-cannula systems, the separated muscle generally reapposed, much like a valve, drawing with it the overlying fascia, frequently to a degree that made it difficult to identify the location of the incision. Consequently, we suspect that this improved preservation of the integrity of the fascial and muscle fibers collectively results in a more secure incision despite the slightly longer incision length. Although it seems clear that in this animal model incisional area secondary to the use of blunt trocar-cannula systems is much less than that from pyramidal devices, we cannot be sure whether these data directly apply to humans. Although the use of systems that result in smaller fascial defects might obviate the need for fascial closure, these data should not be interpreted to support such a conclusion. Other factors not evaluated in the present study might influence trocar-cannula systems–related incision characteristics. The composition of the cannula might vary from very thin steel to thick composites, features that might add or subtract millimeters to or from the outside diameter of the device, despite a similar inside diameter. It is probable that differences in outside diameter of the trocar and cannula that result in a step will contribute to fascial damage at the time of insertion, as well as to difficulty of passage of the device into the peritoneal cavity. The angle of insertion might be important as well. In the present study, a 45° incident angle was used to replicate umbilical entry, the most common approach used by gynecologists. However, in the presence of a double fascial layer, such an angle facilitates an overlapping of the fascial defects, thereby reducing incisional area, at least according to the method used in this study. A 90° insertion angle would result in aligned incisions, potentially creating an incision with a larger overall area. Finally, repeated movement of the cannula during an operative procedure could result in extension or expansion of the wound, either directly or as a result of necrosis of the wound edge. None of these variables has been reported in the past, and none was independently evaluated in the present study. Incisional complications such as hernia and dehiscence are uncommon, perhaps occurring in as few as 21 per 100,000 cases overall but more frequently with 12-mm diameter trocar-cannula systems.3 We suspect that these complications might still be underreported for a variety of reasons, such as failure to diagnose,
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delay in diagnosis, patient tolerance of asymptomatic hernia, and the resistance to publication of negative or adverse results. Although the incisional area associated with blunt 12-mm trocar-cannula systems is statistically significantly less than that associated with either of the similar diameter pyramidal or cutting-dilating systems evaluated, it would be premature to conclude that such incisions do not require closure in clinical situations. However, our findings encouraged us to compare the 12-mm blunt conical devices with narrower diameter pyramidal trocar-cannula systems known to cause low risk for subsequent development of dehiscence or hernia.
References 1. Yuzpe AA. Pneumoperitoneum needle and trocar injuries in laparoscopy: A survey on possible contributing factors and prevention. J Reprod Med 1990;35:485–90. 2. Plaus WJ. Laparoscopic trocar site hernias. J Laparoendosc Surg 1993;3:567–70. 3. Montz FJ, Holschneider CH, Munro MG. Incisional hernia following laparoscopy: A survey of the American Association of Gynecologic Laparoscopists. Obstet Gynecol 1994;84:881– 4. 4. McMurrick PJ, Polglase AL. Early incisional hernia after use of the 12 mm port for laparoscopic surgery. Aust N Z J Surg 1993;63: 574 –5.
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5. Boike GM, Miller CE, Spirtos NM, Mercer LJ, Fowler JM, Summitt R, et al. Incisional bowel herniations after operative laparoscopy: A series of nineteen cases and review of the literature. Am J Obstet Gynecol 1995;172:1726 –31. 6. Kadar N, Reich H, Liu CY. Incisional hernias after major laparoscopic gynecologic procedures. Am J Obstet Gynecol 1993;168: 1493–5. 7. Bhoyrul S, Mori T, Way W. Radially expanding dilatation. Surg Endosc 1996;10:775– 8. 8. Dunn OJ, Clark VA. Applied statistics: Analysis of variance and regression. New York: Wiley & Sons, 1974:115.
Address correspondence to:
Malcolm G. Munro, MD Olive View-UCLA Medical Center Department of OB/GYN 14445 Olive View Drive, Suite 2B-163 Sylmar, CA 91324-1495 E-mail:
[email protected]
Received August 31, 1998. Received in revised form December 21, 1998. Accepted January 7, 1999.
Copyright © 1999 by The American College of Obstetricians and Gynecologists. Published by Elsevier Science Inc.
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