The development of laparoscopic repair for ventral hernias required that the mesh be placed in contact with the viscera. This led to a literal explosion of companies bringing new meshes to market very quickly. The Food and Drug Administration (FDA) is very lenient when it comes to requiring any clinical studies prior to these meshes being introduced (as opposed to drugs) so it is critical that the surgeon understand the pluses and minuses of these different materials since their patients are the “guinea pigs” so to speak. While at one time not too long ago surgeons simply had to choose from heavy-weight polypropylene or polyester they are now confronted with many more choices. With cost being an issue and competition between companies intense, the surgeon is often caught in the middle between the companies and the hospital to make a choice of what meshes to have available. Knowledge of these products is critical.

The three main meshes still available are polypropylene (PPM), polyester, and polytetrafluoroethylene (ePTFE) and various combinations of these materials. The movement to lighter-weight or less dense PPM began in the 1990s when Schumpelick’s group showed that dense PPM stiffened and contracted and that this may be the cause of chronic pain and stiffness of the abdominal wall that some people experience. Ramshaw and the group at Missouri have now taken the next step and are evaluating mesh explants. They have developed a cleaning process to remove adherent tissue without changing the characteristics of the mesh product. They evaluated hundreds of explants and found that as a result of the chronic inflammatory response the mesh is subjected to oxidation. This leads to cracking, changes in thermal properties, weight loss, loss of compliance, and other changes. The explanted material is significantly different from the pristine new product due to oxidation and this, they believe, can explain the problems that surgeons experience clinically. The clinical and experimental work has led to the development of many less dense or what is called lightweight PPM. Many believe that these should be the “new” standard of care when mesh is used and in fact Cobb and Heniford believe that lightweight meshes provide more than adequate strength for repair while resulting in less stiffness and restriction of the abdominal wall. This should be tempered somewhat by a 2005 study of Conze and others who performed a prospective randomized trial of lightweight PPM versus polyester versus regular PPM placed in a sublay fashion as described by Rives. They evaluated the patients out to 2 years and found that complications were the same and the SF-36 scores (assessing physical function and daily activities) were the same between groups. The one thing that was different was that the recurrence rate in the lightweight group
was 17% versus only 7% for the standard meshes. This may have been due to the technique since 19 of the 20 recurrences had absorbable suture used for mesh fixation and three of the eight centers in the study were responsible for all of the recurrences. Either way, more work is needed to address the mesh density question. In addition, the surgeon should remember that a lot of the information on the various meshes comes from animal studies and how these studies correlate with the clinical arena is not known. For example, many animal models show that ePTFE can shrink 25% to 50% when placed on the abdominal wall to mimic hernia repair. This is in sharp contrast to what Schoenmaeckers found in 2009. He had 40 patients who underwent IH repair using ePTFE (DualMesh, WL Gore) and had computed tomography (CT) scans of their abdomen for one reason or another 3 to 59 months later. They had radiologists (blinded to the size of the original implant) measure the transverse diameter of the meshes and found that 28% had no mesh shrinkage and the mean shrinkage of the whole group was only 7.5%.

Barrier meshes with various antiadhesive coatings to prevent ingrowth to the viscera while promoting ingrowth to the abdominal wall had just become available with the last edition of Mastery of Surgery. Now, 3 years later we have more data and more barriers. The first ones on the scene were the coated polyester mesh Parietex Composite (PCO, Covidien) and the coated PPM Sepramesh (Bard) and the coated PPM Proceed (Ethicon). In 2006 Burger looked at these three meshes along with others placed intraperitoneally in 200 rats. They found that in this model the PCO and Sepramesh had fewest adhesions and maximum incorporation into the abdominal wall and were the meshes of choice for intraperitoneal placement. Pierce in 2009, in a rabbit model, looked at these three barrier meshes (at 120 days) in addition to the newest polypropylene barrier mesh by Atrium called the C-Qur mesh. What is important about this study is that they looked at the tenacity of the adhesions, which is a reflection of ingrowth and is our concern. He found all of the barrier meshes worked as advertised. Proceed was the worst with the highest percent of adhesion tenacity and coverage of the group but all barrier meshes were for the most part effective. This is in contrast to a study from 2009 by Schreinemacher who evaluated the barrier meshes (at 7 and 30 days) placed intraperitoneally in a rat model. He found PCO and C-Qur performed the best at 7 days but at 30 days this effect had diminished and there was an increase in adhesions in all of the meshes. Tenacity of the adhesions was not evaluated. Proceed was again the worst performer at both study points. An interesting finding was that none of the meshes had good incorporation into the abdominal wall except at the sites of suture fixation. It appears these antiadhesive coatings work but “second-look” studies are critical to see what happens in the clinical situation. The first clinical second-look study was with DualMesh, an ePTFE mesh. Koehler along with us and several other investigators had the opportunity to do second-look operations in 65 patients who had had ePTFE placed laparoscopically. We found that 91% had no or filmy adhesions and none had severe or tenacious adhesions. In 2006, Chelala published a series of 400 laparoscopic ventral hernia repairs using PCO and was able to have a second look in 35 of these patients. The vast majority had no adhesions or filmy adhesions. In 2010 he updated his results to a total of 85 second-look operations and found similar results. This is the standard that all barrier coated meshes will have to meet.

In my opinion we do not have enough evidence at this point to recommend one type of synthetic mesh over another. They each have their good and bad points and it is important the surgeon be familiar with these issues. PPM, ePTFE, and polyester all have been used very successfully for many years. While they are not perfect, they play a critical role for the herniologist and no one mesh can be ideal for the many different situations the surgeon encounters.

We now have several more years of experience with these meshes. The common theme with these products is to take human or animal tissue, get rid of the cellular component to avoid allergic reaction, and then stabilize the protein structure so it can act as a scaffold. These products are thus a collagen implant that allow native fibroblasts to deposit more collagen to then make a “biologic” mesh. Many of these meshes are expensive and have been brought to market without long-term evaluation as a permanent solution for hernia repair. Many were evaluated only in the animal lab for use other than hernia repair. Patients with increased risk of poor wound healing or known hernia formers may not remodel biologic meshes with healthy collagen. Unfortunately, the various companies have been promoting these products as permanent solutions and they should not be seen as such until long-term studies have been done. Many more meshes have been introduced from animal sources. Some of these meshes have the collagen cross-linked, which retards the degradation of the donor collagen, and the amount of cross-linking is variable. The more the mesh is cross-linked the longer it remains as part of the final scar created. At present we do not know if cross-linking is good or bad and, if good, how much cross-linking is needed. Some of the meshes require refrigeration, some require rehydration, and some have a ventral and dorsal surface for placement.

We have learned a few things over the past several years. The best use of these products is as a sublay or as an onlay with the mesh closely adherent to host tissues. The biologic meshes require vascular ingrowth to survive and this cannot occur if the graft is used as a bridge. If the surgeon uses these grafts as a bridge between fascial edges then the surgeon and the patient should be prepared for a recurrent hernia. This does not mean that you should never use them as a bridge but that it is not the ideal situation. We also know now that products made from dermis with a lot of elastin will stretch over time and while there may be some scar tissue present it is lax and stretched due to the elastin leftover and the patient appears to have a recurrence. Lastly, the biologic meshes can be used in the face of contamination but not overt infection. They will get infected in the face of gross infection and will disappear quickly as they are degraded by the process. There is a new category of mesh just introduced and is made of bioabsorbable polymers. The only product in this category is the WL Gore product called Bio-A. This acts like a biologic in that it disappears but host cells infiltrate the 3D matrix of the mesh and replace it with vascularized soft tissue. Histology shows the tissue is a mix of type I and type III collagen that matures mainly into type I collagen as the wound matures. We have used a small piece of this to reinforce crural closure in 65 paraesophageal hiatal hernias and found it to work very well and have had no problems in the short term. The company has introduced large sheets of this material for use in IH repair. The main advantage of this material over the biologics is that no refrigeration or rehydration is required and it is much less expensive.