Biomaterials in Hernia Repair



Biomaterials in Hernia Repair


N. Joseph Espat



Introduction

Biomaterials, biologics, and biologic mesh are some of the interchangeable terms that have rapidly come into the surgical lexicon in recent years. These terms are intended to differentiate mesh composed in whole or in part of synthetic materials (Prolene, nylon, etc.) from those of “organic” origin (allograft or xenograft dermis, xenograft pericardium or intestinal submucosa, etc.).

The emergence of biomaterials in clinical use was largely due to the need for soft tissue reconstructive materials with tissue-like properties for complex soft tissue defects. Initially, autologous tissues were utilized, that is, tensor fascia lata grafts; however, the amount (area) of tissue available was limited in the individual patient and this led to insufficient material for reconstruction.

As the reader will note, beyond the initial applications of biomaterials as described; even with only limited clinical evidence to support their use for other procedures, over the last decade the use of biomaterials, in large part for hernia repair has been exponential. While there are some data to support the use of biomaterials in the setting of infected, contaminated, or tissue-deficient operative fields, there is no evidence to support the routine use of biomaterials for elective or clean hernia procedures, with the exception of very specific hernias (i.e., paraesophageal). Broadly, hernia categories for which biomaterials are presently in use would include inguinal, postincisional, parastomal, and paraesophageal.

Synthetics: Before proceeding to a discussion on biomaterials, it is important to understand how presently available synthetic meshes are limited, beyond their potential to become infected. The discussion on this concept will be brief and is intended to highlight specific material properties. An ideal prosthetic for postincisional hernia repair should not incite an inflammatory response or foreign body reaction. Similarly, this material should not promote seroma formation, intestinal adhesion, bowel obstruction, or erosion of the prosthesis into an adjacent viscus. Lastly, and most clinically relevant currently, this material should not contract over time and thus not give rise to the current hernia-associated terms, such as “mesh-odyna” and “inguino-dyna.”

Unfortunately, this ideal synthetic prosthetic is not yet available and interestingly it is these same properties that we would want from biomaterials, which are similarly not yet completely available either. Surprisingly, even in the year 2010, our choice of synthetic materials for postincisional hernia repair is largely limited to materials that have been available for more than 50 years, for example, nylon (1944), dacron (1956), polyethylene (1958), ethylene (1958), with the most recent addition to the synthetic armamentarium being polytetrafluoroethylene (PTFE) in 1970. Subsequent “novel” synthetic materials after the 1990s are largely a combination of these standard synthetic materials with a coating or combination of materials intended to prevent bowel adhesions for a short-term period prior to peritonealization. It is based on this need of an optimal reconstructive prosthetic that biomaterials have been touted.

Biomaterials: Between 1999 and the present day, at least 12 separate biomaterials have been approved by the Food and Drug Administration (FDA) for clinical use. In this category of materials, only four have at least a single peer-reviewed publication evaluating outcomes for human use and three for animal use; the remainder lack peer review publications for either human or animal use. In the present work, the presentation will be limited to the use of biomaterials in the repair of complex or contaminated postincisional hernias since it is for this indication that there are the most available data, although predominantly
level 3. Biomaterials for paraesophageal hernia repair have been evaluated by at least one randomized prospective trial, but this specific operation is outside the scope of this chapter.

From a nomenclature perspective, biomaterials can be divided into two large categories: dermal and nondermal in origin. Additionally, these materials can be further subdivided into allograft (human-derived) or xenograft (non-human-origin). Three biomaterials for which there are several peer-reviewed publications for the repair of postincisional hernia and/or abdominal wall reconstruction are presented, and include a dermal allograft, a dermal xenograft, and lastly a nondermal xenograft.

Alloderm ®, manufactured by LifeCell, is harvested human dermis. Because it is derived from human dermis it is composed of a high elastin relative to collagen content, making “stretch” an inherent property of this material. This stretch or relaxation of acellular human dermis, as it is also termed, makes the material strong, pliable, and elastic. Biochemically, the material has been demonstrated to initiate integration, vascular ingrowth, and angiogenesis and is reported to be infection resistant.

Permacol  ®, manufactured by Tissue Science Laboratories/Covidien, is an acellular porcine dermis. Like dermal allografts, there is a high elastin-to-collagen content although the “stretch” of the biomaterial is reported to be approximately 20% to 30% less. The unique property of this dermal xenograft is a process resulting in the chemical cross-linking of the contained collagen, designed to promote increased resistance to collagenase degradation. Based on the instructions for use (IFU) literature on this biomaterial, it is purported to resist absorption and contracture over time; however, there are limited published data available for the use of this biomaterial for postincision hernia repairs and the use of this material has largely been dormant since its introduction in the early 2000s, from a literature perspective.

Surgisis ®, manufactured by Cook Medical, is an acellular porcine small intestine submucosa–derived biomaterial. Anatomically, there is a limited amount of elastin contained within the intestinal submucosa; as such, the material is almost entirely composed of chemically untreated collagen. As can be inferred, the biomaterial demonstrates less stretch and elastic properties compared with dermal-derived biomaterials. Similarly, claims are made relevant to infection resistance and for rapid neoangiogenic vascularization of this biomaterial.

To categorize biomaterials as either human or porcine in origin is not particularly clinically useful. Rather, these materials can again be further broadly classified into materials that are usable in tension-bearing repairs and biomaterials that require a nontension environment. In large part, due to the high elastin content, dermal-derived materials would theoretically perform superiorly in tension-requiring fields and/or repairs for which relaxation, elasticity, and contouring over time are required, properties that are both good and bad. The nondermal materials that are predominantly collagen in composition would be theoretically expected to result in less elastic (compliant) and more rigid repairs over time; again, both a good and bad set of characteristics. It is notable that biomechanical assessment of biomaterial “suture rip strength” has demonstrated that ubiquitously all biomaterials presently available require a stronger force to rip than healthy human fascia.


Anatomy

Surgical repair of an abdominal wall defect originating from a postincisional hernia can be a quite simple operation or one of the most complex procedures that a surgeon will face. The issue of synthetic mesh versus primary repair without mesh for postincisional hernia has been studied in the context of randomized prospective trials. These studies have clearly demonstrated that for postincisional hernia repairs, the long-term recurrence-free outcome is significantly improved by the use of a mesh-reinforced repair in the underlay position.

Further, to define concepts in the present chapter, it is important that the reader understand the terminology utilized for describing biomaterial implantation in the postincisional hernia literature. There are three specific terms: inlay, which denotes that the mesh is sewn directly to the fascial edge and directly into the defect; overlay, in which the mesh is sewn directly on anterior fascial aponeurosis of both edges along the fascial defect; and underlay, in which the mesh is sewn below the fascial edges of the hernia defect onto the posterior aponeurosis with a recommended >3 cm overlap of fascia by the mesh. The documented recurrence rate for hernia repair using these variable mesh positions are as follows: inlay, 20% to 30%; overlay 20% to 40%; and, lastly, underlay <4%, respectively.


Clinical Presentation

The specific clinical settings for which biomaterials can be recommended as an option over synthetic mesh are grossly infected/contaminated fields, or subsequent to the removal of synthetic mesh for infection. Historically, the management of these clinical circumstances was performed by the so-called Fabian approach, described almost two decades ago. In that landmark work, the need for an alternative method of closure for the 5% to 10% of open ventral hernias that would ultimately become infected and require synthetic mesh extraction was discussed. Incorporated into the management algorithm was the very interesting observation from a University of Washington study that observed a 50% to 60% reinfection rate for synthetic mesh materials when placed into a patient after a previous infection. It was for this population of patients that the Fabian approach became popularized. Simply put, this approach requires that in a grossly infected or contaminated field that has not had synthetic mesh put in, or in a similar field from which the synthetic mesh has/is being extracted, the fascia be closed with an absorbable mesh, typically consisting of a polyglycolic acid material intended to promote granulation and prevent evisceration. The skin edges, in keeping with standard surgical practice, are not closed and the wound is allowed to granulate. As highlighted in that article and discussed in subsequent abundant literature, the use of an absorbable mesh is associated with a high frequency of enterocutaneous fistulae, thought to be related to bowel desiccation. These enterocutaneous fistulas typically healed spontaneously and, subsequent to the formation of appropriate bed of granulation tissue, a split-thickness graft would be placed on the wound. Approximately 2 years are required for natural separation of the split-thickness skin graft from the underlying bowel, which then facilitates the surgical removal of the skin graft followed by a reattempted closure with synthetic mesh.

It is important to recognize that synthetic mesh is all that was available in that particular era. The reader can quickly recognize that if a surgical field was repaired using the Fabian approach, that this was, in fact, a contaminated field and that the risk of subsequent mesh infection would have been prohibitively high. It is specifically in this type of clinical scenario that the current use of biomaterials began in earnest.

At present, there is no consensus as to an optimal biomaterial. Level 3 data have demonstrated that outcome is largely dependent on clinical setting, surgeon experience, and patient comorbidities. The use of acellular human dermis in contaminated wounds was initially described by Guy et al.
This initial experience reported approximately 33% overall complications with a 10% reherniation rate at 18 months. Subsequently, Buinewicz et al. described their experience of the use of acellular human dermis in 44 patients, with a similar experience in terms of recurrences along with the observation that 8 of the patients became infected. These two studies were further supported by another small study of 13 patients by Butler et al., with 7 infected and 7 with preoperative radiation therapy, which demonstrated no mesh infections, hernias, or bulges; however, no follow-up was described. In the mid-2000s this was the bulk of literature that was available for the use of acellular human dermis under the category of allografts, highlighting the lack of data to support the present-day utilization of expensive biomaterials.

Similarly, xenograft nondermal small intestinal submucosa has been described for the repair of large fascial defects and to be safely used in contaminated incisional hernia and abdominal wall reconstructions. The basis for these observations arises from the work of Franklin et al. and the series by Ueno, which included 20 patients with hernias in clean or dirty wounds. Seventeen had incisional hernias, all repaired in an open fashion. Six of the 17 were reoperated on for infection and all the infected developed a recurrent hernia within 1 year; however, 66% had no hernia at 1 year.

Only gold members can continue reading. Log In or Register to continue

Aug 2, 2016 | Posted by in GENERAL SURGERY | Comments Off on Biomaterials in Hernia Repair
Premium Wordpress Themes by UFO Themes
%d bloggers like this: