Ventral Hernia – Open Repair

Synthetic Materials.

Various synthetic mesh products are available. Desirable characteristics of a synthetic mesh include being chemically inert, resistant to mechanical stress while maintaining compliance, sterilizable, noncarcinogenic, inciting minimal inflammatory reaction, and hypoallergenic. The ideal mesh has yet to be defined. 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. Mesh constructs can be classified based on weight of the material, pore size, water angle (hydrophobic or hydrophilic), and whether there is an antiadhesive barrier present. When placing a mesh in the extraperitoneal position without the risk of bowel erosion, a macroporous unprotected mesh is appropriate. Both polypropylene and polyester mesh have been successfully placed in the extraperitoneal position. Polypropylene mesh is a hydrophobic macroporous mesh that allows for the ingrowth of native fibroblasts and incorporation into the surrounding fascia. It is semirigid, somewhat flexible, and porous. Placing polypropylene mesh in an intraperitoneal position directly apposed to the bowel is avoided because of unacceptable rates of enterocutaneous fistula formation. Recently, lighter weight polypropylene mesh has been introduced to address some of the long-term complications of heavyweight polypropylene mesh. The definition of lightweight mesh was arbitrarily chosen at less than 50 g/m ² , with heavyweight mesh weighing more than 80 g/m ² . These lightweight mesh products often have an absorbable component of material that provides initial handling stability, typically composed of Vicryl (polyglactin 910) or Monocryl (poliglecaprone 25; Ethicon, Somerville, NJ).

Whether lightweight mesh results in improved patient outcomes is controversial. Two prospective randomized trials evaluating the incidence of postoperative pain after open inguinal hernia repair have shown mixed results. In a randomized controlled trial evaluating lightweight versus heavyweight polypropylene mesh for ventral hernia repair, the recurrence rate was more than twice that in the lightweight group (17% versus 7% for heavyweight mesh), which approached statistical significance ( P = .052).

Polyester mesh is composed of polyethylene terephthalate and is a hydrophilic, heavyweight, macroporous mesh. This mesh has several different weaves that can yield a two-dimensional flat screen–like mesh and a three-dimensional multifilament weave. Unprotected polyester mesh should not be placed directly on the viscera because unacceptable rates of erosion and bowel obstruction have been reported. When placed in the preperitoneal position in complex ventral hernia repairs, complication rates are low.

When placing mesh in an intraperitoneal position, several options are available. A single sheet of mesh with both sides constructed to reduce adhesions, or a composite-type mesh with one side made to promote tissue ingrowth and the other to resist adhesion formation, are available. Single-sheet mesh is composed of expanded PTFE (polytetrafluoroethylene). This prosthetic has a visceral side that is microporous (3 µm) and an abdominal wall side that is macroporous (17 to 22 µm) and promotes tissue ingrowth. This product differs from other synthetic meshes in that it is flexible and smooth. Some fibroblast proliferation occurs through the pores, but PTFE is impermeable to fluid. Unlike polypropylene, PTFE is not incorporated into the native tissue. Encapsulation occurs slowly and infection can occur during the encapsulation process. When infected, PTFE almost always must be removed.

To promote better tissue integration, composite mesh was developed. This product combines the attributes of polypropylene and PTFE by layering the two substances on top of one another. The PTFE surface serves as a permanent protective interface against the bowel and the polypropylene side faces superficially, to be incorporated into the native fascial tissue. These materials have variable rates of contraction and, when placed together, can result in buckling of the mesh and visceral exposure to the polypropylene component. Recently, other composite meshes have been developed that combine a macroporous mesh with a temporary, absorbable antiadhesive barrier. Basic constructs of these mesh materials include heavyweight or lightweight polypropylene, or polyester. Absorbable barriers are typically composed of oxidized regenerated cellulose, omega-3 fatty acids, or collagen hydrogels. A number of small animal studies have validated the antiadhesive properties of these barriers, but currently no human trials exist evaluating the ability of these composite materials to resist adhesion formation.