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New Developments in Hernia Surgery

Author: Karl A. LeBlanc, MD, MBA, FACS

Introduction

The incidence of hernia within the general population is estimated at 3%, with 10% to 15% of cases occurring in adults, predominantly men. Hernia repair is one of the most common elective procedures in general surgery today, with an estimated 700,000 inguinal herniorrhaphies performed annually in the United States alone. In fact, groin herniorrhaphy is the most common operation performed by the general surgeon.

Historically, hernia repair was a sutured repair procedure that created tissue tension and was associated with a relatively high recurrence rate. However, improvements in technique and the development of a range of new prosthetic materials to reinforce the repair have revolutionized hernia surgery and improved patient outcomes.

Recent advances in techniques and devices to repair defects of the abdominal wall may be more numerous than most physicians realize. Approximately 60% of prosthetic repairs of the inguinal floor are believed to use a flat mesh of some type, and the remaining 40% a prosthetic "device" such as a plug or combined plug-mesh system.[6] Additionally, 90% of incisional and ventral hernia repairs incorporate the use of a synthetic prosthesis. This report, drawing on presentations at the American College of Surgeons' 1999 annual meeting, will review the evolution of synthetic biomaterials used for hernia repair, discuss new developments in this area, and detail the impact that the widespread use of these prostheses have had on this common procedure.

Hernia Repair: A Brief History

The earliest record of inguinal hernia dates to 1500 BC.[2] Repair techniques were attempted, usually with poor results, as early as the Middle Ages. It was not until the late 19th century that there were reports of refinement of surgical techniques to repair hernias. Early techniques entailed the use of sutures to close and reinforce the defect. This method of repair is believed to still be used in approximately 10% to 15% of inguinal hernias.[11] Most hernia repairs performed today, however, involve the placement of a synthetic biomaterial --a mesh, plug, or newer variations on these devices -- to reinforce the repair.

A number of these procedures -- currently approximately 15% -- use laparoscopy, although the relative merits of open versus laparoscopic techniques remain the focus of clinical and economic debate.

The use of preformed mesh or related synthetic biomaterials to repair inguinal hernias has become increasingly common since being described by Lichtenstein and colleagues in their report on "tension-free" hernia repair. This approach requires no formal reconstruction of the canal floor with the sheet of polypropylene mesh (PPM) used as an onlay graft. This technique can be used for both indirect and direct inguinal hernias. The rate of hernia recurrence was found to be lower with this technique compared with sutured repair.

Prosthetic Materials for Hernia Repair

Prosthetic products, natural and synthetic, have been used in herniorrhaphy for decades. Surgeons considered and rejected numerous types of implants before settling on the range of materials most widely used today.

Natural Prosthetic Biomaterials

Implants composed of natural biomaterials (Table 1) were first considered as a substitute for the normal myofascial tissues as early as 1910.

Table 1: Natural Prosthetic Biomaterials

Some of these were used with fairly successful results, but their scarcity and, in many cases, cost limited their being adopted widely.

Metal Synthetic Biomaterials

Use of metal synthetic biomaterials (Table 2) predated the development of natural implants. Unfortunately, these were difficult to handle in surgery and were associated with poor resistance to infection, frequent abscess formation, and recurrent herniation. As a result, none found broad acceptance.

Silver filigree disappeared from the scene because of discomfort related to lack of pliability, tendency to become hardened by work, accumulation of fluid around the material, wound infection, and subsequent sinus tracts. Tantalum gauze mesh developed fatigue fractures, associated patient discomfort, abnormalities of the abdominal wall contour, herniation through fractures, seroma

formation, and dense adhesions to underlying bowel and was difficult to remove. Stainless steel mesh may have been a viable alternative in terms of infection, but such metal prostheses are rarely used today in hernia repair because of concerns about structural integrity and allergic reactions.

Table 2: Metal Synthetic Biomaterials

Nonmetallic Synthetic Prostheses

Experimentation with a series of nonmetallic synthetic materials (Table 3) yielded a few that showed promise, but many others had significant drawbacks and thus were not widely adopted. These include the following:

     Fortisan fabric (cellulose). Became infected with abscess and sinus formation.

     Polyvinyl sponge. Firmness and rigidity were altered in vivo, and it was poorly tolerated by the body in the presence of infection.

Nylon mesh. Proved unreliable in infection, had poor fibrous ingrowth, lost its strength due to hydrolysis and chemical denaturing in vivo.

Silastic. Mainly used in pediatric repair of omphalocele and gastroschisis. Adequate fibrous tissue ingrowth was one of its advantages.

Polytetrafluoroethylene. Original mesh was not incorporated well into body tissues and was not tolerant of infection. Had a high rate of wound complications.

Carbon fiber. Advantages include biocompatibility and inducing formation of new connective tissue similar to ligaments.

     Questions as to potential carcinogenicity have precluded its clinical use.

Table 3: Nonmetallic Synthetic Prostheses

The Modern Age of Hernia Repair

The modern age of hernia repair began 40 years ago, with the first use of a monofilament-knitted polyethylene mesh to lessen tissue tension. The mesh prosthesis reinforced a previously sutured repair.

This key event was followed by the introduction of polypropylene mesh (PPM), which heralded a significant advance in the synthetic biomaterials available to hernia surgeons.

The development of PPM, which was easier to handle than previously existing synthetic materials, spurred additional research during the subsequent three decades into other synthetic biomaterials that could be used in a similar fashion (Table 4).

Table 4: Current Synthetic Biomaterials

For hernia repairs in particular, there are a number of important clinical characteristics of prosthetic biomaterials to consider.

These include the material's ability to restore the integrity of the abdominal wall, its permanence, ease of handling, degree of incorporation into native tissues, foreign body reactivity, resistance to infection, and ability to conform to the native structures its covers. Surgeons should take these various characteristics into account in selecting an implant.

In their efforts to develop synthetic implants for use in hernia repair, researchers have referenced the properties noted by Cumberland and Scales as the ideal characteristics of such materials (Table 5).

Table 5: The Ideal Characteristics of Synthetic Biomaterials

Additional useful criteria for future implant development would be the ability of a prosthesis to provide a barrier to adhesions on the side of the material placed adjacent to the abdominal viscera and to respond in vivo more like autologous tissue. This latter characteristic would allow tissue incorporation for good fixation and a strong lasting repair without encouraging scarring and

encapsulation problems seen with current prostheses.

Today's Prosthetic Biomaterials

There have been few changes in hernia repair technique that do not make use of a prosthesis, although one presentation at the American College of Surgeons' meeting did outline one such evolution. In this method of repair,[24] reported in a poster session, modification of the inguinal anatomy was used to repair the floor in such a manner that was reported as "physiologic." In this technique, the cord is transposed and a neo-orifice is created. The author reported favorable results with most types of inguinal hernias.

Most of the biomaterial products available for use in hernia repair today are variations on older products that feature improvements in the design and/or shape of the various biomaterials used previously. A detailed review of these materials and their various forms follows.

Polyester Mesh

Polyester mesh was introduced about 30 years ago and continues to be used today, although mostly in Europe. These prostheses are supple and elastic, conform to the visceral sac, have a grainy texture to grip the peritoneum and prevent slippage, and are sufficiently reactive to induce rapid fibroblast response to ensure fixation. There have been reports recently of significant problems with the use of polyester biomaterials in some patients.

Sofradim International has introduced a new concept in the polyester biomaterials that are used to repair defects of the abdominal wall. A new device, with only limited use in Europe, Parietex, features a woven biomaterial that is unlike any of the other meshes (Figure 1 and Figure 2); the difference lies in the two- and three-dimensional structure as seen under the electron microscope. It remains to be shown conclusively that the change in the structure and weave of the polyester biomaterial offers lasting improvements over the current products.

Polypropylene Mesh

The prosthetic meshes now available include those that have been used for many years in the repair of both inguinal and incisional hernias, the first having been the monofilament weave of PPM (Marlex) described by Usher. These materials and their manufacturers are listed alphabetically in Table 6. The original Marlex remains available and continues to be used (Figure 3), but a newer variation, the more loosely woven Visilex (Davol, Inc), has since been introduced for use in laparoscopic repairs. Visilex

has a reinforced edge that aids manipulation of the material when it is placed into the preperitoneal space (Figure 4).

Table 6: Polypropylene Biomaterials

The option of laparoscopic repair has prompted other modifications to older PPM products. In 1993, Surgipro multifilament mesh was reconfigured to become the Surgipro open knit monofilament mesh (United States Surgical Corporation, Inc), a product designed for laparoscopic repairs. Similarly, Ethicon has constructed the PROLENE polypropylene biomaterial into a looser weave of PPM. This was released in July 1999 and is called PROLENE polypropylene mesh -- new construction (Figure 5).

This change was designed to make the product more supple and easier to handle. Other flat PPM materials that remain relatively unchanged from the original include Atrium mesh and Trelex mesh.

A new material available in Europe is Paritene (Sofradim). Also a monofilament PPM, Paritene has enlarged interstices (Figure 6), which are designed to provide multidirectional elasticity, making it less dense and less rigid than older PPM biomaterials.

Expanded Polytetrafluoroethylene

W.L. Gore & Associates, which originated the expanded polytetrafluoroethylene (ePTFE) prosthesis, continues to manufacture the Soft Tissue Patch (Figure 7) in both 1- and 2-mm thickness. A similar material is available in the Bard line of hernia products, the Reconix patch (Figure 8). This product has a gross appearance identical to the Gore-tex Soft Tissue Patch, but its microscopic appearance differs greatly, with a laminated structure and different porosity (Figure 9 and Figure 10). These differing characteristics may affect the amount of tissue in-growth. Either product can be placed via a laparotomy (incisional, ventral hernia) or laparoscopic approach (incisional, ventral, or inguinal hernia).

MycroMesh is a new generation of the ePTFE prosthesis that was introduced by Gore in 1993. This prosthesis is a reconfiguration of the company's Soft Tissue Patch, which has textured surfaces and pores that are spaced throughout the material (Figure 11). This construction is designed to permit the passage of fibroblasts and collagen, thereby permitting greater fixation of the product to the natural tissues.

The DualMesh prosthesis available from Gore since 1994 is a two-sided ePTFE product. One surface has an interstitial spacing of 3 mcm and serves as a barrier to tissue incorporation (Figure 12), thus minimizing adhesion formation. The other side has 17- to 22-mcm interstices, which allows the in-growth of tissue fibroblasts and collagen (Figure 13). The development of this biomaterial provided for its use in incisional and ventral hernia repair. Because of this product, the laparoscopic method of this repair is becoming more popular since first reported in 1993. This product has since been modified; the "in-growth" surface now has larger interstices and a rough, "corduroy-like" surface when viewed grossly. This rough surface should foster much greater tissue incorporation (Figure 14), although clinical data documenting this characteristic are not yet available.

The MycroMesh Plus, DualMesh Plus, and DualMesh Plus with Holes patches are distinguished by the incorporation of silver and chlorhexidine in the biomaterial to reduce the risk of infection. The addition of these chemicals results in a brown or gray tone to the products, which aids laparoscopic manipulation. The only study that has examined the potential side effects of the dissolution

of the chemical agents within the tissues found no adverse effects.

Composite Products

Adhesions represent the primary complication related to the use of PPM prostheses within the abdominal cavity, although obstruction, bowel erosion, and fistula formation also have been known to occur.  In addition, ePTFE has not been associated with significant problems, such as bowel erosion and fistula formation. Some surgeons are reluctant to use some of the older ePTFE products, however, because of concerns about the lack of tissue in-growth and cost. Two new products attempt to address

surgeons' desires for dense tissue incorporation afforded by PPM while attempting to limit the risk of adhesion formation.

Composix mesh (Bard) consists of a sheet of Marlex with a thin layer of ePTFE on one surface (Figure 15). The PPM side is attached to the abdominal wall, and the ePTFE surface will contact the bowel. This is designed to provide good tissue incorporation on the PPM surface while diminishing the likelihood of obstruction and fistulization where the ePTFE comes into contact with the abdominal contents, although there are no long-term clinical data available as yet to confirm this outcome.

Composix may be used in either the open or laparoscopic methods of repair of the ventral hernias. It is very thick, however, which makes it difficult to insert via laparoscopic trocars.

Parietex composite mesh is another new material that attempts to mitigate the potential adverse effects of the bowel-prosthetic interface (Figure 16). This product, available only in Europe at this time, is a combination of a three-dimensional weave of polyester with a hydrophilic collagen material. The resorbable collagen layer is designed to prevent development of intra-abdominal adhesions, and the product can be used in either open or laparoscopic incisional and ventral hernias. Clinical outcomes studies on the product have not yet been published.

Preformed Shapes (PPM)

The advent of the laparoscopic approach to repair defects of the inguinal floor has led to many modifications in the instruments used by surgeons. Similarly, the flat prosthetic meshes available for hernia repair have been modified to accommodate the preperitoneal space that is dissected during the laparoscopic inguinal herniorrhaphy. One example is the Bard 3D Max mesh (Figure 17), a three-dimensional and anatomically formed prosthesis specifically designed for use in laparoscopic inguinal hernia repair. Features of this product are a crest to conform to the inguinal ligament and a notch for the iliac vessels; these reportedly allow for easier positioning and minimize the recurrence rate.

The Kugel Hernia Patch (Surgical Sense, Inc., Arlington, Tex), which has a lengthy clinical history, is used in open repair of the posterior abdominal wall (Figure 18). This prosthetic device is an oval, flat piece of PPM with a "memory recoil ring" of polyester that the manufacturer claims allows the patch to open fully to cover the entire inguinal floor. Use of this device requires a thorough knowledge of the posterior wall of the inguinal canal and a fair amount of tissue dissection for insertion. It is purported to reduce patient discomfort and recovery time, as does laparoscopic repair in general. The product can also be used for the open repair of smaller ventral hernias. A recently published study reported good results with this approach, with minimal recurrence.

The Sofradim company has two products made of Paritene and Parietex described as "anatomical" mesh devices that conform to the inguinal floor (Figure 19 and Figure 20). These devices are constructed into a shape that has two distinct purposes: one portion conforms to the anterior abdominal wall and the other to the iliac and iliopubic tract areas of the preperitoneal space. This particular product is designed for laparoscopic inguinal hernia repair.

Plugs (PPM)

The use of "plugs" to repair defects of the inguinal floor has an established history, and this form of herniorrhaphy has become very popular in the United States.

This herniorrhaphy method appears to have a short learning curve, can be performed under local anesthesia, and has had good results as reported by Robbins and Rutkow. This repair can be used for primary and recurrent inguinal hernias. However, it requires the introduction of the plug into the preperitoneal space, which may be less appealing to some surgeons. This method of herniorrhaphy includes a patch that is placed anterior to the groin musculature as an integral part of the procedure. This emulates the tension-free repair that has been used for many years before the plug.

The Bard PerFix plug is an umbrella-shaped, multipleated device that is formed into the shape of a cone. It is manufactured from Marlex PPM and comes in several sizes to accommodate the various-sized defects of the inguinal floor. The patch aspect of the repair system is simply a flat sheet of Marlex prosthetic biomaterial.

Other plug and patch systems are available (Table 7) and similarly come in various sizes to repair the defects into which they are placed.

Table 7. Plug and Patch Systems

The Hernia-Mate plug system is made of the monofilament PPM and is also cone-shaped. This product is not pleated and consequently may be slightly more "deformable," suggesting it would better fill the defect.

The Atrium Self-Forming mesh plug has several characteristics that differentiate it from other plug systems (Figure 21 and Figure 22). This device consists of three layers of the Atrium PPM that are bonded together at the 12-, 3-, 6-, and 9-o'clock positions. A tab is affixed to the center of the circular, unfolded plug. This allows the surgeon to grasp the plug for the insertion into the defect in the inguinal canal. The plug then assumes the size and shape of the defect. As in the other plug repairs, a patch

of PPM is placed over the anterior inguinal floor in the manner of the tension-free herniorrhaphy.

Bilayered Patch Device (PPM)

The benefits of the open tension-free method (placing a prosthetic mesh anterior to the muscle) and those of laparoscopic approach (placing the mesh posterior to the muscle) are exploited in the "bilayered" repair. Most inguinal hernia repairs are approached from the anterior aspect, but laparoscopy allows the surgeon to repair the inguinal floor from the posterior surface.

This prosthetic device allows the surgeon who is not familiar with the laparoscopic approach to the inguinal floor to provide the patient with a repair that is similar in concept. This avoids some of the risk of the laparoscopy and the need for a general anesthetic and appears to have a similar diminution in the postoperative pain and disability. The PROLENE polypropylene Hernia System (Ethicon, Inc., Somerville, NJ), released in January 1998 (Figure 23), was designed to take advantage of this opportunity.

This hernia repair system is based on the older form of the PROLENE polypropylene PPM. Two flat portions of PPM are connected by a PPM cylindrical plug. The round portion of the system is placed in the preperitoneal space to cover the posterior wall. The elongated portion is placed anteriorly over the internal oblique muscle. The connector then acts as a plug to fill the defect of the inguinal musculature. To accommodate variations in inguinal anatomy, this device is made in three sizes. The size differentiation relates to the elongated portion that will overlie internal oblique. Clinical outcomes with this device have been favorable.

Conclusion

General surgeons today have access to a wider and more sophisticated range of synthetic biomaterials for use in hernia repair than ever before. The advantages and disadvantages of each of these devices must be understood, however, before surgeons select any of these implants.

King reported that overall strength, suture-retention strength, extensibility, thickness, flexibility, and porosity are important factors in determining the ability of surgical mesh to reinforce wounds. Stiff or wrinkled mesh, for example, can be difficult to apply or cause postoperative complications.

Meanwhile, a 1997 study of various biomaterials used in abdominal wall hernia repair further reported that the risk of infection, seroma formation, biomaterial-related intestinal obstructions, and other complications can be minimized or eliminated by understanding the process underlying these problems and taking proper precautions.

The surgeon's choice of the prosthesis used in hernia repair is based on a combination of factors, including patient characteristics; clinical experience, training, interest, and skill; understanding of the range of products available and the clinical studies that may have been performed on each; and the surgeon's familiarity with a particular product and/or surgical approach. The clinical studies

that will bring additional levels of confidence to the decision-making process are now under way.

Innovations in technique and product design will no doubt continue to spur advances in hernia repair, and it is hoped that they will continue to improve outcomes. The availability of these outcomes data, along with the ongoing accumulation of clinical experience with a broad range of materials and techniques, will help surgeons to better identify the most appropriate prosthesis for the clinician and the patient.

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