Introduction

Pelvic organ prolapse and urinary incontinence are common conditions in women. Eleven percent of the female population will undergo surgery for prolapse or stress incontinence in their lifetime ( ). Approximately 30% of these women will need a repeat operation for urinary incontinence, recurrent prolapse, or complications related to the first surgery. No standard surgical approach is available to patients who suffer from recurrent pelvic organ prolapse and/or incontinence. Multiple surgical techniques for recurrence, some incorporating surgical implants of synthetic or biologic graft material, have evolved, and some investigators have recommended the use of graft material or prosthesis for surgeries to repair recurrent prolapse. Since the introduction of the first commercially available, trocar-guided mesh augmentation system or “mesh kit” for vaginal prolapse in 2004, the use of implants, both synthetic and biologic, in vaginal reconstructive pelvic surgery has expanded rapidly in spite of a lack of clear indications supporting their use. In 2010, it was estimated that 300,000 procedures were performed for prolapse with 70,000 vaginal mesh procedures, 196,000 traditional vaginal reconstructive surgery without mesh augmentation, and 34,000 abdominal procedures with mesh.

The increased use and wide adoption of vaginal mesh procedures from 2005 to 2010 was due in part to the marketing of commercially available mesh kits. General gynecologists and urologists, who were not subspecialty trained and did not usually perform prolapse procedures such as sacrospinous colpopexy and vaginal paravaginal defect repairs, were taught to use these mesh kits during industry-sponsored cadaveric anatomy and surgical technique courses. Because many of these kits require attachment of mesh arms to arcus tendineus fasciae pelvis and/or sacrospinous ligament, it is imperative not only to have knowledge of the relevant anatomy, but also to have experience dissecting in these areas, surgical skills that many general gynecologists and urologists do not have. Consequently, in 2008, after more than 1000 voluntary reports of safety problems to the Manufacturer and User Facility Device Experience database, the Food and Drug Administration (FDA) released a public health notice regarding complications and adverse events associated with the use of mesh in prolapse and stress incontinence procedures. In 2011, the FDA released a safety communique that updated the public health notification and concluded that “serious complications associated with surgical mesh for transvaginal repair or pelvic organ prolapse are not rare” and “it is not clear that transvaginal pelvic organ prolapse repair with mesh is more effective than traditional non-mesh repair”. The FDA further recommended that vaginal mesh surgery should be selected “only after weighing the risks and benefits of surgery with mesh versus all surgical and non-surgical alternatives.” The FDA, along with leaders from professional societies including the American Urogynecologic Society, also agreed that mesh use in stress urinary incontinence surgery is standard of care. Recently, the vaginal mesh devices were changed from class 2 to 3 devices by the FDA and thus are being investigated by 522 postsurveillance studies for associated safety and efficacy.

The 2nd International Urogynecological Association (IUGA) Grafts Roundtable convened in 2010 and made several recommendations regarding patient variables and vaginal use of graft/mesh ( ). Because most of the information on patient characteristics is based on expert opinions, the decision of whether to use vaginal graft/mesh augmentation should be individualized. The following are some of IUGA’s findings:

• 1.
  

  Age: The age cutoff for patients in whom graft/mesh is indicated or contraindicated remains unclear, with one study finding a 2.2-fold increase in mesh exposure rate in women older than 60 years of age ( ).

  
  
• 2.
  

  Recurrent prolapse: Although most experts agreed that repair of recurrent prolapse cases may result in higher recurrence risks and these cases may need to be managed differently than primary prolapse, most studies do not make this distinction in their analysis.

  
  
• 3.
  

  Compartment and severity of prolapse: The use of graft/mesh may depend on the site and severity of prolapse. As discussed elsewhere in the chapter, although there may be an anatomic benefit to graft/mesh augmentation in the anterior compartment, this may not be the case for the posterior compartment. Additionally, because there may be an association between severity of prolapse and increased recurrence risk after surgery, some experts would consider mesh placement in cases of severe prolapse.

  
  
• 4.
  

  Connective tissue deficiency: There may be a role for graft/mesh augmentation in patients with connective tissue disorders as conditions such as joint hypermobility, Marfan’s syndrome, and Ehlers-Danlos syndrome have been associated with prolapse.

  
  
• 5.
  

  Chronic increases in intraabdominal pressure: Women with conditions such as chronic constipation and/or with occupations that require heavy lifting may be at risk for prolapse and may benefit from graft/mesh augmentation.

  
  
• 6.
  

  Chronic pain/dyspareunia: Although the main risk factor for pain after surgery is pain before surgery, de novo postoperative pain and dyspareunia has been reported with graft/mesh augmentations. Furthermore, removal of the implanted material does not always lead to complete pain resolution; therefore, graft/mesh augmentation in these patients should be cautioned.

  
  
• 7.
  

  Pregnancy: Because there is limited information on graft/mesh augmentation in patients who become pregnant after implantation, these procedures should not be performed in patients anticipating becoming pregnant in the future.

  
  
• 8.
  

  Diabetes: Poorly controlled diabetes may place patients at increased risk for impaired healing after surgery and graft/mesh exposure.

  
  
• 9.
  

  Steroid use: Chronic steroid use may be associated with delayed tissue healing, which may affect graft/mesh exposure.

  
  
• 10.
  

  Tobacco use: In one study, smokers were 3.7-fold more likely to develop mesh exposure ( ).

  
  
• 11.
  

  Increased body mass index (BMI): Obese patients undergoing vaginal surgery have been found to be at increased risk for developing wound infections. In one study, women with BMI greater than 30 were 10.1-fold more likely to develop mesh exposure ( ).

  
  
• 12.
  

  Concurrent vaginal hysterectomy and inverted T colpotomy: Women were more likely to develop mesh exposure if a concomitant vaginal hysterectomy was performed and if an inverted T colpotomy was used, with one study finding a 5.2- and 6.1-fold increase in risk, respectively ( ).

Vaginal graft/mesh augmentation should only be performed by skilled surgeons with experience and training in these procedures because increased experience has been associated with fewer complications, including mesh exposure. Surgical techniques specific to these types of procedures include making sure that the mesh is not placed under tension because mesh may contract after placement. However, the ideal method of tensioning is not clear. Synthetic mesh should be placed without wrinkles within the fibromuscular connective tissue layers, well under the vaginal epithelium. Although a biologic graft may be placed over a traditional plication as a reinforcing layer, synthetic mesh used in this fashion may be associated with increased exposure. Removal of excess vaginal epithelium after these procedures should be limited because of tissue contraction. Additionally, women with vaginal atrophy may benefit from treatment with vaginal estrogen before surgery to improve healing.

Good evidence supports the use of implantation of synthetic material for abdominal treatment of pelvic organ prolapse, as noted in Chapter 21 . Midurethral sling procedures using synthetic materials have similar cure rates compared with autologous rectus fascia slings, but with fewer complications. The tension-free vaginal tape (TVT) procedure, a polypropylene mesh midurethral sling, has gained widespread popularity; it has proven effectiveness comparable to Burch colposuspension and is considered the gold standard treatment for urodynamic stress incontinence. However, the use of synthetic or biologic implants in transvaginal reconstructive procedures is less clear as most of the studies are case series or prospective cohort studies and different types of grafts are used. Although there are now multiple studies, including randomized controlled trials, addressing the use of implants for vaginal repair of anterior or posterior compartment prolapse, there are several limitations with these studies and with comparing different studies:

• 1.
  

  There are often many variations in surgical technique both in traditional repairs as well as in vaginal mesh procedures, even the ones that involve commercially available mesh kits (e.g., different methods of tensioning of mesh) making comparison between different studies difficult.

  
  
• 2.
  

  There is no standard definition of success in the different trials.

  
  
• 3.
  

  Because the ideal mesh or graft does not presently exist, studies may have used many different types of mesh. Even if type I polypropylene mesh is used, because this type of mesh is commercially available in different weights, knitted differently, with different rigidity and elasticity and the total surface area may be different in different procedures, it is not clear if these variables have impact on surgical outcomes.

  
  
• 4.
  

  Many studies include a heterogenous patient population such as patients with primary and recurrent prolapse.

  
  
• 5.
  

  Many studies, especially older studies, included only anatomic outcomes without including validated quality of life questionnaire results.

  
  
• 6.
  

  The traditional repair control may not be a truly adequate control. For example, because advanced anterior compartment prolapse is often associated with apical prolapse, a traditional anterior colporrhaphy without apical suspension may not be an adequate control to a vaginal mesh procedure that involve anchoring an anterior vaginal mesh to the sacrospinous ligament and/or arcus tendineus fasciae pelvis.

  
  
• 7.
  

  Follow-up periods are usually short, 1 year or less.

  
  
• 8.
  

  Most trials involve fewer than 200 patients.

  
  
• 9.
  

  The experiences or learning curves of surgeons performing mesh kits are not always fully stated or taken into account in data analyses.

Because this is very much an area of active research, and recommendations on graft/mesh usage are still evolving, it is possible that by the time this chapter is published, expert consensus may be different than what is presented in this chapter. Presently, several manufacturers promote various types of synthetic and biologic materials. No adequate studies comparing different implants are known. In this chapter, we will review properties of the ideal graft material, host tissue, and available implants. The surgical procedures that involve mesh implantation, associated clinical results, and complications will also be summarized.

Properties of the Ideal Graft Material

Authors have proclaimed a need for ideal graft materials since the mid-twentieth century, and the search continues today. The ideal graft would be chemically and physically inert, noncarcinogenic, mechanically strong, sterilizable, not physically modified by body tissue, readily available, inexpensive, and have minimal risk of infection and rejection ( Box 28.1 ). In prolapse and incontinence surgery, the optimal implant, once healed, would restore normal anatomy and function to the vagina and surrounding pelvic organs. It would be biocompatible and, if biodegradable, persist long enough to allow a durable and adequate repair and incorporation of the surrounding tissue. It would be resistant to mechanical stress or shrinkage and be easy to work with and pliable. Other desirable criteria include availability in the desired shapes for various operations, prevention of adhesions at visceral surfaces, and a better, or at least equal, response to implantation compared with autologous tissue. Unfortunately, at present, none of the synthetic or biologic tissue implants meet all of these criteria.

There are few published articles that directly compare synthetic and biologic implants in human subjects. One study compared porcine dermal sling to the TVT procedure ( ). For sacral colpopexy, compared polypropylene mesh to solvent dehydrated cadaveric fascia lata and then later compared polypropylene mesh to porcine dermis ( ). Literature regarding the physical properties of implanted materials is confined to animal studies and has been rarely comparative, previously analyzing abdominal wall implantation, then a rabbit vagina model ( ), and most recently, vaginal implantation in primates. were successful in using a rabbit vagina model to study graft material tensile strength after implantation. It does appear however that there is marked variation in biomechanical characteristics of various meshes available to surgeons ( ).

The most clinically relevant data pertaining to mesh implantation in vivo were published by and . These parous primate studies compared high-stiffness heavy polypropylene mesh (Gynemesh PS ^® , Ethicon) with newer low-stiffness lightweight polypropylene meshes (Smartmesh (Coloplast) and Ultrapro (Ethicon)) and sham operations. The meshes were implanted during sacrocolpopexy following hysterectomy. The mesh–vagina complexes were then harvested after 3 months. Active mechanical and passive mechanical properties were assessed. Vaginal contractility decreased the greatest with Gynemesh PS ^® compared with the other meshes; Smartmesh resulted in the greatest contractility ( ). Deterioration of the mechanical properties of the vagina was highest with the stiffest heaviest mesh.

The same laboratory investigated histomorphology in this group of parous primates. Relative to sham and the two lower-stiffness lightweight polypropylene meshes, Gynemesh PS ^® had the most negative impact on histomorphology and composition, resulting in greatest thinning of vaginal smooth muscle after implantation, increased apoptosis, decreased collagen and elastin content, and increased total collagenase activity. Glycosaminoglycan, a marker of tissue injury, was highest with Gynemesh PS ^® compared with the other meshes and sham operations. The observed maladaptive tissue response to the heavy-stiffness mesh is consistent with vaginal degeneration ( ).

Biologic Properties of Host Tissue

Before discussing properties of various implants, the role of connective tissue in the pelvic floor must be described. eloquently summarized the biologic properties of host connective tissue. This supportive structure contains fibrous elements (collagen and elastin) and a viscoelastic matrix containing proteoglycans (large polysaccharides attached to proteins). Connective tissue cells determine the biomechanical properties of soft tissue and are embedded in the extracellular matrix, which comprises 20% of the tissue volume. Collagen, a protein produced by fibroblasts, is composed of glycine, proline, and hydroxyproline. Glycine allows collagen to form a tight helix, whereas proline and hydroxyproline form cross-links to stabilize the collagen chains. Tensile strength of tissues is attributed to collagen fibers. Two fibers found in tissue that require strength and flexibility are type I (the most plentiful and strongest) and type III (less common and randomly organized with type I). Elastin and laminin are glycoproteins that are thought to play a role in a tissue’s ability to stretch. Several authors have shown that the metabolism of collagen and/or elastin is disrupted in various pelvic floor disorders.

After reconstructive surgery, fibrous protein synthesis and remodeling reestablish tissue strength with collagen playing a central role in wound healing. Immature fibroblasts synthesize and secrete collagen and proteoglycans within 24 h of surgery. During the first 2 weeks after reparative surgery, type III collagen is the principal type found. With maturation of scar tissue, a stronger type I collagen replaces type III collagen. Elastin is not synthesized and remodeled to the extent that collagen is by humans. Scar tissue resulting from wound healing after surgical repair is never as strong as the original tissue that it replaces.

For the scope of this chapter, it is important to summarize the reaction of host tissue to implanted materials. Biocompatibility is defined as the capability of a material to cause a favorable reaction in a living system, thus performing, augmenting, or replacing a natural function in the host. described four types of soft-tissue response: (1) minimal response with a thin layer of fibrosis around the implant, (2) chemical response with severe and chronic inflammatory reaction around the implant, (3) physical response with an inflammatory reaction to certain materials and the presence of giant cells, and (4) necrosis resulting from in situ exothermic polymerization.

Four stages of histologic reaction to graft implantation have been described by . They are:

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  Stage 1—During week 1, an intense inflammatory infiltrate around the implant, capillary proliferation, granular tissue, and the presence of giant cells ensues.

  
  
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  Stage 2—Within 2 weeks, granular tissue remains and foamy histiocytes appear. The number of giant cells with foreign body graft fibers may increase or decrease.

  
  
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  Stage 3—Up to week 4, the acute inflammation disappears, capillaries are reduced, and the number of foamy histiocytes and giant cells increase.

  
  
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  Stage 4—After week 4, a few collections of giant cells are present on the surface of the implant, and dense fibrous tissue is present.

Properties of Synthetic Material

The available absorbable synthetic mesh implants are polyglycolic acid (Dexon, Davis & Geck, American Cyanamid, Danbury, CT) and polyglactin 910 (Vicryl, Ethicon Inc., Somerville, NJ). Absorbable implants may be desirable because they promote postoperative fibroblast activity, are less threatened by infection, do not undergo rejection, and are not known to be harmful to viscera. showed that fibrous deposition into polyglactin mesh cannot take place before its absorption. Polyglactin 910 starts to hydrolyze during the third week after implantation and loses the majority of its mechanical value after 30 days. Polyglycolic acid requires 90 days for absorption. Macrophage activation results in mesh absorption and subsequent recycling of by-products into new collagen fibers ( ). The resultant scar tissue is not as strong as the reinforced tissue, as evidenced in animal studies ( ).

Nonabsorbable (permanent) synthetic mesh implants are either monofilament or multifilament ( Fig. 28.1 and Table 28.1 ). The most important physical properties of synthetic implants are pore size and porosity. Some authors have noted small intrafiber pores (interstices of less than 10 μm) as a disadvantage of multifilament mesh in comparison to monofilament mesh ( ). Most bacteria are less than 1 μm in diameter in comparison to granulocytes and macrophages, which are greater than 10 μm in diameter. The pore size plays an important role in mesh infection prevention and fibrous ingrowth of surrounding tissues. When describing the characteristics of synthetic mesh, listed type of polymer, weave, type of filament, weight, and pore size as important. The authors emphasized that the pore size is the key factor in determining inflammatory response, fibrocollagenous tissue ingrowth, angiogenesis, flexibility (or stiffness), and strength. Best mechanical anchorage with collagen infiltration was noted with pore size between 50 and 200 μm. noted that exact pore sizes of various meshes cannot be quoted because measurement is technique-dependent.

Pore configuration of various synthetic implants. A , Marlex. B , Mersilene. C , Prolene. D , Gore-Tex. E , Gynemesh-PS. F , IVS.

(Figures A-D reprinted with permission from Iglesia CB, et al. The use of mesh in gynecologic surgery. Int Urogynecol J . 1997;8:105.)

Marlex reportedly has the highest flexural rigidity when compared with Mersilene, Teflon, and Prolene. Both Marlex and Prolene are monofilaments, although Prolene is more flexible because of its larger pore size. Magnified views of six types of synthetic mesh are displayed in Fig. 28.1 .

Synthetic mesh has been classified as types I to IV, with respect to pore size, as described by . Because of various problems associated with microporous and multifilament synthetic grafts, all nonabsorbable grafts in use for female pelvic reconstructive surgery are type I macroporous grafts. Refer to Table 28.1 for various grafts and associated properties.

• 
  

  Type I—is macroporous (pore size >75 μm).

  
  
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  Type II—is microporous (pore size <10 μm) in at least one of its three dimensions.

  
  
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  Type III—is a macroporous material with multifilamentous or microporous components.

  
  
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  Type IV—is submicronic (pore size <1 μm); this type of mesh is often associated with type I mesh for adhesion prevention in intraperitoneal implantation.

All types of synthetic mesh have high tensile strength (more than 50 N) and all polypropylene mesh is not type I. Type I mesh acts as a scaffold for tissue ingrowth (fibroblastic cell infiltration). Pore size greater than 90 μm reduces inflammation, and type I mesh has been associated with reduced rates of infection. Reduced inflammatory responses should decrease erosion. Marlex mesh has a smaller pore size and thus has poor tissue ingrowth. Type II and III meshes result in greater foreign body reaction when compared with type I mesh. noted that microporous mesh had ongoing perimesh inflammatory reaction at 18 months. Microporous and macroporous multifilament meshes appear to be associated with greater infection rates and poor tissue ingrowth that is attributed to fiber makeup or less surface tension. Microporous multifilament mesh, such as Gore-Tex, is associated with a high infection rate and foreign body reaction. At this time, the most evidence-supported synthetic material for implantation in the pelvic floor is type I macroporous, lightweight, low-stiffness polypropylene mesh; however, currently available grafts do not possess all qualities of the previously described ideal implant.

Implant structure was outlined by . The mechanical properties depend on the structure of the fabric and the thread. These materials can be woven, knitted, or unwoven. Plain, twill, and satin are the three types of woven materials, and their advantages are strength and good memory ( Fig. 28.2 A ). The disadvantages of woven structures are fraying and poor conformity. Knitted fabrics consist of warp knit, interlock, and circular knit ( Fig. 28.2 B ). The advantages of knitted materials are flexibility, versatility, and high conformity. The unwoven materials are well-absorbed but have the disadvantages of no conformity and poor visibility. Composite structures have two surfaces, one of which prevents adhesions. The disadvantages of these fabrics are that they are rigid and poorly visible. Implants can have perforations and be molded into various shapes: kidney, umbrella, or a plug. Materials can be structured from monofilament or multifilament fibers, which can be twisted, coated, braided, or double-braided ( Fig. 28.3 ). reported mechanical properties of eight types of synthetic implants available in Europe from a study performed in collaboration with the engineering department of Institut Catholique des Arts et Métiers; however, they acknowledged that no recommendations exist regarding desired resistance or elasticity of various implants and this holds true in 2014. Certain materials had differing values based on orientation (lengthwise or widthwise); however, too little is known about how various mechanical properties of mesh contribute to the function and longevity of a reparative procedure.

A , Woven mesh. B , Knitted fabric.

(Adapted with permission from Cosson M, Debodinance P, Boukerrou M, et al. Mechanical properties of synthetic implants used in the repair of prolapse and urinary incontinence in women: which is the ideal material? Int Urogynecol J . 2003;14:169.)

Fiber structure.

(Adapted with permission from Cosson M, Debodinance P, Boukerrou M, et al. Mechanical properties of synthetic implants used in the repair of prolapse and urinary incontinence in women: which is the ideal material? Int Urogynecol J . 2003;14:169–178.)

The recent studies by and on parous primates support lightweight low-stiffness macroporous polypropylene mesh for improved vaginal contractility and tissue response when compared with heavier weight, higher stiffness meshes. A composite mesh has been available for use in pelvic reconstructive surgery. This mesh is composed of a monofilament polypropylene mesh coated with a hydrophilic porcine collagen (Pelvitex ^® , C.R. Bard Inc., Covington, GA), but it is no longer available in the United States. The hydrophilic, absorbable coating protects the viscera from risk of adhesion formation during the first 10 to 14 days after surgery when inflammatory processes peak. Although few data are available regarding the use of this mesh in pelvic floor procedures, adhesion formation has been minimized in abdominal hernia repair ( ). This mesh is also a lightweight monofilament polypropylene thought to maintain strength, increase flexibility, and decrease mesh load on the tissues. A lighter weight and load of mesh may decrease erosion. Most recently, an “ultralight” 17 g/m ² weight mesh in a Y-configuration has been prospectively studied with short-term follow up to 12 months showing no graft complications or mesh erosion ( ).

Properties of Biologic Tissue

Autologous grafts can be harvested, but allograft, xenograft, and synthetic materials are widely available, and the morbidity associated with autologous tissue procurement can be undesirable in some patients. Although synthetic materials eliminate the morbidity associated with the donor site, they have a higher risk of exposure or erosion compared with allografts (biologic tissue procured from a source other than the recipient) and xenografts (biologic tissue procured from a source or species foreign to the recipient). Despite few data to support this intervention, some surgeons routinely use biologic tissue because they consider the host tissue impaired or insufficient for successful reconstruction (although for slings, host tissue is well proven to be effective). The biologic grafts include cadaveric dermis, cadaveric fascia lata (CFL), and collagen matrix laminates—usually from porcine dermis, porcine small intestine submucosa, bovine pericardium, and, recently applied to pelvic floor surgery, porcine bladder muscularis extracellular matrix (MatriStem, ACell Inc., Columbia, MD) ( Fig. 28.4 ; Table 28.2 ). Each product differs in the type of processing and sterilization techniques, giving biologic graft materials varying biomechanical and physiologic properties. Various abbreviations for biologic tissue used in this chapter are listed in Box 28.2 .

Biologic tissue implants.

Implantation of xenografts has gained popularity in reconstructive pelvic surgery because of concerns regarding availability of human allograft tissue and risk of viral transmission. Porcine dermal allografts (DAs) have been used in cardiothoracic and general surgery for many years. The intended goal of human allograft and xenograft tissue is to provide a scaffold of acellular biocompatible material to allow infiltration and subsequent replacement of graft tissue by the regenerated functional host cells. This acellular material consists of a bioactive and absorbable extracellular tissue matrix consisting of proteins, collagen, elastin, and various growth factors. Acellularity is a desired quality rendering the tissue incapable of eliciting an inflammatory response by its implantation (nonimmunogenic), thus decreasing risk of infection and erosion after graft implantation. However, published data refute that various biomaterials are cell-free. showed the presence of porcine DNA in small intestinal submucosa (SIS) implants for tendon repair. This cellular characteristic may increase risk of rejection and infection after implantation. reported that freeze-dried (FD) and Tutoplast CFL retain donor class I and II human leukocyte antigen. proved that FD gamma-irradiated CFL and acellular cadaveric DA tissue contained intact DNA. used extraction techniques and DNA amplification to show that four commercially processed human allografts contained intact genetic material. This is of particular concern because of the theoretic transmission of prions during allograft implantation. Prions are small proteinaceous infectious particles that resist inactivation by procedures that modify nucleic acids. Despite the previous findings of intact DNA and antigens, there have been no reported cases of disease transmission after allograft implantation.

Tissue processing is very important; however, no consensus exists on the methods that should be implemented to produce the ideal biomaterial. Materials are sterilized by various processes, which include freeze-drying, solvent dehydration, or gamma irradiation. An investigation by emphasized that little is known regarding the effect of sterilization techniques on the structure, mechanical strength, and biocompatibility of biomaterials. The authors showed that all sterilizing methods of SIS (ethylene oxide, gamma irradiation, and e-beam irradiation) resulted in an increase in the rate of sample degradation. They hypothesized that sterilization techniques resulted in the release of extractable growth factors. reported a 17% early sling failure rate with FD-CFL, although numerous investigators have refuted their findings with the use of similar biomaterials.

Some biomaterials have been “cross-linked” to delay reabsorption, a property that various manufacturers promoted for success of graft augmentation procedures (a premise that has been proven incorrect by a randomized trial of rectocele repair ( )). A potential long-term problem with aldehyde cross-linked implants is that they may develop foci of mineralization (calcification) that can become extensive. Calcification of implants prompted one publication by that evaluated the influence of two anticalcification pretreatments on glutaraldehyde cross-linked bovine pericardium in rats. Currently marketed bovine pericardium (Veritas ^® , Synovis, St. Paul, MN) is not cross-linked with glutaraldehyde. Aldehydes are also cytotoxic at higher levels. One porcine dermis product is cross-linked and stabilized with hexamethylene di-isocyanate (HMDI), making it more permanent and resistant to breakdown by collagenases produced by inflammatory cells and fibroblasts. Animal studies in rats have shown no evidence of mineralization after HMDI cross-linked porcine dermal graft implantation at 2 years ( ). Thus, whether cross-linking, despite prolonging a graft’s existence, renders it more effective in reconstructive surgery is unknown. Aldehyde cross-linked implants should be avoided because of mineralization. The majority of currently available biomaterials used for pelvic floor repair are not cross-linked. Some biologic tissues are fenestrated to ensure porosity and to enhance fibrocollagenous ingrowth and angiogenesis. Fenestrations are thought to decrease the risk of seroma formation and infection associated with graft implantation. Therefore, some companies recommend fenestration/perforation of the graft before surgical implantation and others have fenestrated biologic grafts as part of routine processing.

The following is a summary of the data regarding histologic properties of various types of biologic tissue after implantation. showed that autologous rectus fascia (ARF) persists, neovascularizes, and remodels consistent with noninflammatory scar tissue. Once implanted, the ideal biologic tissue (allograft or xenograft) would be physiologically identical to ARF. However, in animal studies, ARF has shown shrinkage by 50% and reduction in tensile strength in up to 30%. Although the histologic fate of AFL has not been reported, some authors have shown tissue remodeling in patients who underwent sling revision. Animal data showed that FD-CFL remodels and is replaced with parallel bundles of host collagen at 12 weeks ( ). Meaningful histologic studies for solvent-dehydrated (SD) grafts have not been published. In animal studies, DA has been shown to have greater thickness than SIS at 4 months after implantation.

Most investigations of biomechanical properties of various biologic tissue and mesh measure tensile strength as an end point. Whether this is an adequate test is unknown for comparison of the biomechanical properties of biomaterials once implanted in the pelvis. A model that measures compliance and burst strength of the vagina may be more physiologic. showed greater tensile strength with AFL when compared with ARF because of longitudinal versus transverse fibers. The maximum load to failure of ARF was consistent with SD CFL and DA. FD-CFL (gamma-irradiated) has less tensile strength than the previously mentioned biologic tissues and has been shown to lose 90% of its tensile strength after implantation in the rabbit model. compared autologous tissues (dermis, rectus fascia, and vaginal mucosa), cadaveric tissues (decellularized dermis, and FD gamma-irradiated CFL), and synthetic materials (Gore-Tex and polypropylene mesh) used in sling procedures and evaluated full strip slings versus patch suture slings. They found that in rank order for the full strip slings, cadaver allografts had the strongest tensile strength followed by the synthetics and autologous tissues. The tensile strength for the full strip slings was significantly greater than for the patch suture slings. In rank order for the patch slings, the synthetics and dermal tissues (autograft and allograft) had the highest tensile strength followed by AFL, ARF, and vaginal mucosa. When a patch sling is constructed from autograft and allograft tissues, the risk of suture pull-through and recurrent stress incontinence must be considered. investigated six materials for comparison of tensile strength, stiffness, shrinkage, and distortion after implantation in rabbit rectus fascia: two types of CFL (Tutoplast ^® , Mentor Corp., Santa Barbara, CA; LifeNet, Virginia Beach, VA), porcine SIS (Stratasis ^® , Cook Urological Inc., Spencer, IN), deepithelialized dermis (Derm Matrix ^® , Carbon Medical Technologies, Saint Paul, MN, now Intexen, American Medical Systems, Minnetonka, MN), polypropylene mesh (SPARC ^® , American Medical Systems), and ARF. The authors showed that human cadaveric fascia and porcine allografts showed a marked decrease (60-89%) in tensile strength and stiffness from baseline. Polypropylene mesh and autologous fascia did not differ in tensile strength from baseline. Comparison of TVT and CFL in an in vivo rat model showed that TVT mesh has a greater break load and maximum average load than CFL ( ).

In conclusion, porcine SIS and FD-CFL have the lowest tensile strength before implantation when compared with other biologic tissues and synthetic mesh. Patch slings are more susceptible to suture pull-through than full-length slings. Autologous fascia and polypropylene mesh are the only graft materials in comparative animal studies that do not weaken after implantation. None of these findings, however, can be extrapolated to clinical outcome data in humans.