Hernia repair is one of the most common surgical interventions performed by general surgeons. It is estimated that 5% of the population will develop an abdominal wall hernia, but the prevalence may be even higher.
The word “hernia” derives from the Latin word for “rupture” and it is defined as an abnormal protrusion of an internal organ through a defect in its physiological cavity. Although a hernia can occur at multiple sites of the body, these defects most commonly involve the abdominal wall. In broad terms, most abdominal wall hernias can be separated into ventral (umbilical, epigastric, Spigelian, lumbar, and incisional) and groin hernias (femoral or inguinal), the latter being more frequent, comprising about 75% of all hernias.
Hernias may develop for different reasons. The main risk factors for abdominal wall hernias include obesity, family history, pregnancy, injuries to the bowel area, and constant lifting of heavy objects.
Their treatment is fundamentally surgical. In recent years there have been rapid advances in our understanding of the biological basis of hernia development, surgical technique for repair and, most significantly, the use of prosthetics.
Historically, there has been a long evolution leading to the development of the modern hernia meshes. At the end of the 19th century, Phelps, Goepel and Witzel for the first time attempted inguinal hernia repair using a silver wire braided mesh. Other attempts using gold, silicon and other materials experienced many complications and were quickly abandoned. These early meshes were far from ideal. However, after the introduction of polypropylene by Nobel Prize winner Giulio Natta together with Karl Ziegler in 1954, this material was adopted for hernia repair and rapidly became widespread in the surgical community. Nowadays, it is one of the materials most frequently used for hernia repair.
The introduction of prosthetic meshes in hernia repair drastically reduced the recurrence rate and has now become an accepted practice in the treatment of patients with both inguinal and ventral hernias. Numerous randomized comparative trials as well as meta-analyses and comprehensive reviews have unequivocally shown the superiority of prosthetic repairs over pure tissue repairs when considering recurrence.
Classification of mesh types
Prosthetic meshes can be classified into two main categories:
- Synthetic meshes:
- 1. Reticular.
- 2. Laminar.
- 3. Composite meshes
- Biological meshes or bioprosthetic.
Various synthetic mesh products are available. The ideal mesh has yet to be defined, but the desirable features of a synthetic mesh include:
- Being chemically inert.
- Resistance to mechanical stress while maintaining compliance.
- Non carcinogenic.
- It should incite minimal inflammatory reaction.
When selecting the appropriate mesh, the surgeon must consider the position of the mesh,
whether it will be in direct contact with the viscera, and the presence or risk of infection.
Reticular meshes are macroporous, with pores that range from 1 to 4 mm. They are mostly made of polypropylene (PP), but also of polyester and polytetrafluoroethylene (PTFE).
PP mesh is a hydrophilic macroporous mesh that allows the ingrowth of native fibroblasts and their incorporation into the surrounding fascia, encouraging rapid ingrowth of connective tissue. Because of this, it has a high tensile and bursting strength and provides a strong mechanical reinforcement. The disadvantages of the PP mesh are that the intensity of foreign-body reaction has been thought to cause reduced compliance and increased pain, and most importantly, adhesion formation if in contact with the viscera, so it is appropriate for an extraperitoneal position without the risk of bowel erosion.
Polyester meshes have not been as widely adopted worldwide as PP meshes, even though they are usually employed in some European countries with satisfactory results. They also cause rapid fibroblastic infiltration and fixation to the surrounding tissues, with the advantage of less mesh shrinkage when compared to PP meshes. Nevertheless, polyester meshes have been associated with higher rates of infection, loss of strength over time, and also adhesion to viscera when placed in an intra-abdominal position.
Laminar meshes are essentially made of expanded polytetrafluoroethylene (PTFEe), which is a microporous, hydrophobic material composed of compact nodules interlinked by fine fibers. This material has good biological tolerance and generates a minimal inflammatory response compared to PP or polyester. It produces good mesotelization and creation of a satisfactory neoperitoneum. Because of this, it is a better prosthetic material to place in contact with the peritoneum or viscera and it is commonly used for laparoscopic intraperitoneal hernia repair.
As a disadvantage, this kind of mesh lacks good tissue incorporation – connective tissue does not infiltrate the mesh, but rather encapsulates it -, so the mesh/tissue interface is worse compared to reticular meshes, which leads to higher recurrence rates.
To bring together in a single mesh the tissular response of reticular and laminar meshes, composite meshes were created using more than one material, and they are the basis of most new mesh designs. They combine the attributes of PP and PTFE by layering both substances on top of each other. They have a macroporous surface on the non-visceral side of the mesh which provides mechanical strength and promotes collagen accumulation and ingrowth, and an internal layer with a microporous surface in the visceral side facing the peritoneum, whose primary role is to avoid adhesion to the viscera.
Other composite meshes have been recently developed that combine a macroporous mesh with a temporary, absorbable anti-adhesive barrier. Basic constructs of these mesh materials include polypropylene or polyester, and absorbable barriers are typically composed of oxidized regenerated cellulose, omega-3 fatty acids, or collagen hydrogels.
This type of mesh is used to repair large hernia defects when there is a lack of tissue support and a total reconstruction of the abdominal wall is required. In these cases, the mesh will usually be located in contact with the visceral peritoneum.
Biological meshes or bioprosthetics
In the last decade, meshes of biological origin have been studied as possible alternatives to synthetic materials. Bioprosthetics are acellular collagen matrices whose main goal is to provide the extracellular components needed to complete healing, allow for the reconstruction of new and healthy tissue, and restore mechanical and functional integrity to the abdominal wall.
There are several types of biological meshes available in the market. They can be classified depending on whether the tissues are animal (xenogenic) or human (allogenic), the kind of tissue they are made of (dermis, pericardium, intestinal submucosa), and the processing methods (stripping, cross-linking).
Biological meshes have shown many advantages, including a milder immune response, a decreased incidence of fistulae, and reduced fibrosis. However, there are some concerns with the use of biological materials such as their supposedly inferior mechanical strength and higher cost of production.