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Mesh: Material Science of Hernia Repair
Mesh is defined as a network of interlaced material with a lattice-like structure, which in medicine has become synonymous with use for reinforcement of hernia repairs. Mesh use has become ubiquitous as inguinal hernia repair (IHR) is one of the most common procedures performed in the world. Additionally, IHR is the most common type of hernia operation performed, with an estimated 700,000 performed annually in the United States alone. The core principles of IHR remain the same regardless of which technique is performed (excision of the hernia sac tension, reduction of intraabdominal contents, and tension-free closure); however, the methods used between various surgical approaches and individual techniques differ significantly. An open approach via groin incision is still the most common IHR performed in the United States, and the modified Lichtenstein repair has become the most common open repair type since its introduction in 1984. In addition, the majority of repairs are now performed with a prosthetic mesh, as its use in an open repair has reduced hernia recurrence from 7% to 1%. Laparoscopic repairs inherently require the use of mesh and have had an increasing utilization in the past 20 years as laparoscopic education and training have increased.
Incisional and ventral hernia repair (VHR) is also one of the most common surgical procedures performed around the globe, with an estimated 350,000 performed in the United States and 300,000 performed in Europe per year. Both IHR and VHR are one of the top five procedures performed by graduating general surgery residents consistently each year. Mesh reinforcement of hernia defects was popularized by the work of Usher who first described the use of polypropylene (PP) mesh, and today, mesh use is ubiquitous in VHR. However, few surgeons understand the inherent differences in the materials and properties of the mesh they use every day, the evolution of mesh technology and material science, different scenarios in which a certain mesh may be most effective, and most importantly, that mesh choice can effect critical patient outcomes.
Therefore the goal of this chapter is to describe the evolution and history of mesh for use for hernia repair, the physical properties on which we evaluate mesh, the underlying materials used to construct them, the classification schemas used to differentiate mesh, the nonmesh adjuncts being used in combination with and used to fixate mesh, new technologies used to construct mesh (especially biologic and absorbable synthetic mesh), as well as the inherent risks and complications that can result due to mesh implantation. Additionally, we hope to focus on evidence-based scenarios and recommendations on when and what type of mesh is appropriate.
History
Hernias have been recognized as medical problems since the time of the Egyptians in 1500 bc and have gone through a long evolution of treatment. The Greeks and Romans were the first to realize that inadequate technique in surgical abdominal closure was linked to incisional hernias, and Galen was the first to describe mass closure techniques in the second century ad . Galen also advocated for use of the paramedian incision to prevent incisional hernia, a technique now proven to reduce hernia rates. In the 18th and 19th centuries, hernias were described and differentiated in detail by anatomists, but not much headway was made in the operative repair of hernias until after the advancements in anesthesia and antisepsis in the late 19th century that allowed for modern aseptic and general anesthetic techniques. This allowed for complex tissue repair techniques such as the Bassini repair, which is still in use today.
Modern hernia repair is characterized by the use of mesh reinforcement, which was popularized in 1958 by the work of Usher who first described the use of PP mesh. Lesser known was that the first artificial mesh implant was actually performed in 1900 by Goepel and Witzel using a silver wire braided weave, which resulted in stiff, nonfunctional abdominal walls, which also had the deleterious side effect of toxic sulfur silver buildup. Subsequently, stainless steel or tantalum gauze was used in the early 20th century, but these were plagued with high infection and complication rates. It was not until the dawn of plastic science after World War II and the creation of PP, polyester, and polyfluoroethylene (PTFE) and expanded polyfluoroethylene (ePTFE) that suitable materials were present for the creation of malleable, pliable, and durable meshes with relatively low complication rates.
In 1968, Rives and Stoppa described broad mesh reinforcement of groin hernias using Dacron grafts and then applied this technique to large abdominal wall defects with mesh in the retrorectus position, which was popularized in the 1980s. The onlay technique was first described by Chevrel in 1979, which involves mesh being placed superficial to the anterior rectus fascia following suture repair of the fascial defect. Another mesh technique, intraperitoneal mesh placement, was previously looked upon unfavorably due to the risk of mesh erosion into viscera and formation of fistulas. However, with creation of barrier-coated meshes and use of biologic and absorbable synthetic meshes, intraperitoneal mesh placement is now ubiquitous and the way most laparoscopic VHR is performed. The first laparoscopic VHR repair was described by LeBlanc in 1993, and recently, the field of robotic surgery has provided an opportunity to explore advanced minimally invasive techniques; the first robotic VHR was described in 2003.
Perhaps even more significant than minimally invasive techniques, the introduction of biologic-derived mesh and absorbable synthetic mesh has changed the playing field for hernia repair. Interestingly, the first biologic reinforcements for hernia repair were with frozen cadaveric dermis, tensor fasciae latae, and dural mater tissues in the 1930s and 1940s, but these had poor results. The renaissance of the biologic mesh came about in the early 2000s when acellular dermal matrix (AlloDerm; Allergan, Dublin, Ireland) was created from cadaveric human dermis for use in reconstructive and burn procedures. Later it was studied for potential use in VHR in contaminated fields first in a pig model and then for use in stoma site hernias in humans. With the use in hernia repair solidified, the number and type of biologic mesh developed has exploded in the last decade with various tissue sources, xenografts, allografts and now even absorbable synthetic, and biosynthetic created meshes. Where in previous years there were only a handful of mesh options, now the number of meshes available gives surgeons a plethora of options in how best to repair hernias tailored to specific patients.
Evidence for Mesh Repair
Mesh reinforcement for hernia repair is a much less debated topic than in prior decades, and it is currently standard of care in developed nations given the high rate of hernia recurrence with primary tissue repairs. IHR with mesh has been studied for longer than VHR, with the first randomized control trial dating from the 1990s, and several meta-analyses showing that the risk of hernia recurrence is reduced 50% to 75% with mesh reinforcement compared with tissue repair alone. The landmark study on this topic in VHR by Luijendijk et al. in 2000 described a 43% hernia recurrence rate at 3 years with suture repair compared with a 24% rate for mesh repair, which increased to 63% recurrence at 6 years. Numerous studies have verified these results, and a recent meta-analysis clearly demonstrated that mesh repair results in less recurrence. Most surgeons acknowledge that it is standard of care to perform VHR with mesh. Despite this, there have been some proponents of performing primary VHR with component separation alone without the use of a prosthetic mesh to buttress the repair. However, recurrence after VHR with component separation alone can result in inferior outcomes and is reported to occur anywhere from 5% to 23% in short-term follow-up of 2 years.
Mesh Categories
Materials science for mesh has come a long way since the time of silver wire weaves, and in the past 15 years, the market for number and types of mesh has multiplied exponentially. The original synthetic plastic mesh repair described by Usher was with a Marlex mesh composed of PP, and since that time, hernia mesh has evolved from this single synthetic material to three broad classes of materials: permanent synthetic, biologic, and absorbable synthetic. Each category of mesh has its own benefits and drawbacks that make it ideal in certain situations. To guide the use of mesh selection, the Ventral Hernia Working Group published a grading scale for hernias by level of hernia and patient complexity and contamination: grade 1 hernias are clean fields in low-risk patients without significant comorbidities; grade 2 are clean fields but with patient comorbidities including diabetes, smoking, and obesity; grade 3 are potential contamination such as the presence of an ostomy, enterotomy, prior wound infection; and grade 4 are mesh infection present or a septic wound.
In general, synthetic mesh is ideal in lower grade hernias, and biologic mesh should be used in higher-grade hernias. The use of these meshes to avoid mesh infection of synthetic mesh should be balanced with the much higher financial cost associated with biologic mesh, as well as the higher hernia recurrence rate, as these meshes stretch over time. Indeed, in lower risk, lower grade hernias, synthetic mesh has been found to be more cost effective than biologic mesh. For this reason, mesh companies have developed new mesh materials that have biochemical scaffolds that will dissolve over time and allow for tissue ingrowth: so-called absorbable synthetic, resorbable, or biosynthetic mesh (terms vary in literature).
Synthetic
Material
The first plastic synthetic mesh was originally composed of PP, which is a permanent monofilament carbon polymer that is flexible and biologically inert. PP is composed of hydrophobic polymer with alternating methyl moieties. The monofilament nature allows for large pores, which facilitates tissue ingrowth and less interstices for bacteria to set up biofilms, which are more likely the smaller the pore and in multifilamentous mesh. The majority of commercially available mesh is still made from PP, but various evolutions of the original monofilament large-pore mesh have been created. An in situ image of a PP knit mesh for IHR is displayed in Fig. 55.1 . The body uses the PP as a lattice to build scar tissue on, which is the process for tissue reinforcement, but it is also a drawback if it is placed in direct contact with the viscera. Adhesion formation can be severe if placed intraperitoneally, resulting in bowel obstructions and mesh erosion into bowel. Therefore, coatings have been added to PP to prevent visceral adhesion formation when it is placed in body cavities.
After the introduction of PP meshes, PTFE and ePTFE meshes were synthesized. PTFE is a sheet of hydrophobic inert fluoropolymer that the body does not incorporate into but encapsulates around as a foreign body. One reason for this is that the material is highly negatively charged, so water and oils will not adhere to the material. PTFE is generally not currently used since the introduction of ePTFE. This material is more microporous than PTFE but still does not allow for tissue ingrowth when made as a flat sheet. The principal advantage of ePTFE is that it can be placed directly onto viscera and not form adhesions, as depicted in Fig. 55.2 . This must be balanced with the fact that it is highly susceptible to bacterial colonization in addition to seroma formation. Most surgeons would recommend that infected ePTFE must always be explanted. To combat the issue of poor tissue incorporation, different-sided ePTFE mesh has become available in DualMesh (Gore Medical, Flagstaff, Arizona), which allows textures of ePTFE with a corduroy side for more surface area for tissue incorporation and a smooth side for visceral contact. An electronic microscope image of the corduroy side is seen in Fig. 55.3 .
Polyester mesh was created after PP and ePTFE, but while available, is not generally used in the United States, since it has similar properties to PP mesh. It is created from polymers of terephthalic acid, which is hydrophilic and can be degraded by hydrolysis. Commonly available synthetic mesh categorized by physical properties are displayed in Table 55.1 .
TABLE 55.1
Synthetic Mesh
| Material | Barrier Strategy | Weight Category | Filament | Structure | Pore Size | Mesh Brand Name | Additional Comments |
|---|---|---|---|---|---|---|---|
| Polypropylene | None | Light | Mono | Knit | Macro | Bard Soft | For all hernia repair types, Soft is lighter weight, larger pore, Plug version available |
| Light | Mono | Knit | Macro | Prolene Soft | For all hernia repair types, Soft is lighter weight, larger pore | ||
| Light | Mono | Weave | Macro | Progrip | Self-gripping mesh for laparoscopic IHR facilitated by polylactic acid mesh component, absorbs over 18 months, tacking not required | ||
| Light | Mono | Weave | Macro | 3D Max Light | Contoured mesh for laparoscopic IHR, Light version is lighter weight | ||
| Light | Mono | Knit | Macro | Prolite, Prolite Ultra | For IHR, Ultra is lighter weight, larger pore | ||
| Light | Mono | Weave | Macro | VitaMesh Blue | For all hernia repairs, dyed blue for better visualization | ||
| Light | Multi | Knit | Macro | Ultrapro, Ultrapro Advanced | Monocryl as one of the filaments, absorbs over 2 weeks, leaving 70% of mesh | ||
| Light | Multi | Weave | Macro | Vypro, Vypro II | Polyglactin 910 as one of the filaments, absorbs over 4 weeks, leaving 70% of mesh | ||
| Mid | Mono | Knit | Macro | Bard | For all hernia repairs, Kugel patch for IHR and UHR, Visilex for LVHR, Plug version available | ||
| Mid | Mono | Knit | Macro | Prolene | For all hernia repair types, Soft is lighter weight | ||
| Mid | Mono | Weave | Macro | VitaMesh | For all hernia repairs | ||
| Mid | Mono | Weave | Macro | 3D Max | Contoured mesh for laparoscopic IHR, Light version is lighter weight | ||
| Mid | Mono | Knit | Macro | Prolite | For all hernia repairs | ||
| Heavy | Mono | Knit | Intermediate | Marlex | Original PP mesh, for all hernia repairs | ||
| O3FA | Mid | Mono | Knit | Macro with barrier | C-QUR, C-QUR V-patch, C-QUR CentriFX | PP coated in O3FA, V-patch for UHR, CentriFX for IHR | |
| Titanium | Mid | Mono | Weave | Macro | TiMesh, TiLene, TiSure | Titanium oxide bonded to PP filaments in titanization process, no actual barrier, for all hernia types | |
| ORC | Mid | Mono | Knit | Macro with barrier | Proceed | UHR and VHR versions, ORC layer absorbed in unknown time period | |
| Seprafilm | Mid | Mono | Weave | Macro with barrier | Sepramesh | For VHR and UHR, Seprafilm absorbs within 30 days, replaced by Ventralight mesh | |
| Hydrogel | Mid | Mono | Weave | Macro with barrier | Ventrio, Ventralex ST, Ventralight ST | Ventrio and Ventralex ST for UHR, Ventralight for VHR, similar to Seprafilm technology, absorbs over 30 days | |
| ePTFE | Heavy | Mono | Sheet | Micro | Composix, Ventralex, Ventrio | Ventralex for UHR, Composix for VHR, PP abdominal side to facilitate ingrowth, ePTFE for visceral side | |
| Polyester | None | Heavy | Mono | Knit | Intermediate | Dacron | Outdated, not routinely used |
| Heavy | Mono | Knit | Intermediate | Mersilene | Outdated, not routinely used | ||
| Collagen | Mid | Mono | Knit | Macro | Symbotex | 3D coated monofilament, for intraperitoneal placement | |
| Mid | Multi | Knit | Macro | Parietex | Collagen-coated polyester mesh to prevent adhesion formation | ||
| ePTFE | None | Heavy | N/A | Sheet | Micro | Gore-Tex | Original ePTFE mesh |
| Heavy | N/A | Dual sided sheet | Macro/Micro | Dulex | Larger pores on the abdominal side, microporous on the visceral side to inhibit adhesions | ||
| Heavy | N/A | Dual sided sheet | Micro | DualMesh | Corduroy microporous abdominal side and smooth microporous visceral side |
ePTFE, Expanded poly(tetra)fluoroethylene; IHR, inguinal hernia repair; LVHR, laparoscopic ventral hernia repair; Macro, macroporous, Micro, microporous; O3FA , omega 3 fatty acid; ORC, oxidized regenerated cellulose; PP, polypropylene; UHR , umbilical hernia repair; VHR, ventral hernia repair.
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