**5. The failure of PPL in the pelvic floor**

The first use of polypropylene in the pelvic floor was based on the integral theory [44]. The integral theory of female stress urinary incontinence stated that the pubourethral ligament in women creates a physiologic 'backboard' by fixing the mid-urethra to the pubic bone and that the laxity of this ligament results in the loss of the backboard inhibiting the urethral coaptation during times of increased intra-abdominal pressure that results in urinary incontinence. The synthetic midurethral slings (MUS) based on the integral theory came as a minimally invasive treatment modality with very high success rates. The initial description of the methodology used plastic tapes with the patient under local anesthesia [31]. The high initial success rates of the minimally invasive, relatively easy to perform MUS operations soon led to the use of the PPL mesh for transvaginal repair of pelvic organ prolapse.

The POP occurs as a result of loss of support at three levels in the pelvis. Level I cardinal-uterosacral ligaments providing apical support, level II arcus tendineus fascia pelvis supporting middle part of vagina laterally and level III urogenital diaphragm and perineal body supporting lower part of the vagina [45]. The contribution of each of these structures to occurrence of prolapse as we see it in the clinic, is not well defined. A recent work, for example, suggests that lack of vaginal apical support was a significant contributor to the occurrence of anterior compartment prolapse and that correcting the apical descent when treating cystoceles would reduce re-operation rates [46]. Thus the exact pathophysiology of POP, its correlations with clinical presentations and the theoretical basis of surgical techniques performed to treat POP are not well described. Nevertheless most of POP repair procedures are performed via a vaginal route (transvaginally) [47] either by placing the mesh directly on to the native tissue repair or suturing it to a strong ligament such as the sacrospinous ligament or arcus tendinous fascia pelvis [17]. Regardless of at what level the defect is and what the mesh restores, the transvaginal POP repair is more reflective of an onlay technique (mesh onlay repair) which did not work very well in the abdomen arguably due to being prone to be colonized by skin microbial flora as it lies very close to the skin [48]. Additionally, the mesh is not placed on a well vascularized wound bed in mesh onlay vaginal repairs. This can have particular importance in the postmenopausal women undergoing these operations as they already have poorly oestrogenised tissues.

In addition to the limitations related to the surgical technique of implantation, the PPL mesh also has some inherent characteristics that make it unsuitable for use in pelvic floor. Recent animal studies in sheep confirmed a site specific response to implanted PPL mesh, where a 5 × 5 cm piece of PPL mesh led to contraction and erosion in 3 out of 10 sheep in 12 months when implanted vaginally in contrast to no erosions in abdominal implantations [49]. The animal studies also showed that the host response to the PPL initiated by macrophages in the mesh-tissue interface was mainly an M1 (proinflammatory) response, instead of an M2 (remodeling) response, characterized by secretion of matrix metalloproteinases and pro-inflammatory cytokines leading to a vigorous foreign body reaction [50]. An M2 response is favorable for tissue integration while an M1 dominated response is now thought to explain the pain associated with mesh and mesh exposure. Clinical data obtained from women who underwent mesh excision due to severe pain or mesh exposure also confirmed that there was an M1 predominant macrophage response observed in the histological sections of the mesh-vagina explants [51]. Essentially a high M1 response indicates persistent inflammation. Thus there is a site-specific response to PPL mesh and the failure of PPL in the pelvic floor is partially due to the unfavorable mesh-tissue interaction leading to poor tissue integration.

**5. The failure of PPL in the pelvic floor**

40 Pelvic Floor Disorders

use of the PPL mesh for transvaginal repair of pelvic organ prolapse.

The first use of polypropylene in the pelvic floor was based on the integral theory [44]. The integral theory of female stress urinary incontinence stated that the pubourethral ligament in women creates a physiologic 'backboard' by fixing the mid-urethra to the pubic bone and that the laxity of this ligament results in the loss of the backboard inhibiting the urethral coaptation during times of increased intra-abdominal pressure that results in urinary incontinence. The synthetic midurethral slings (MUS) based on the integral theory came as a minimally invasive treatment modality with very high success rates. The initial description of the methodology used plastic tapes with the patient under local anesthesia [31]. The high initial success rates of the minimally invasive, relatively easy to perform MUS operations soon led to the

**Figure 1.** Graphical demonstration of surgical implantation sites of mesh material in relation to muscle and fascia in abdominal hernia repairs. (A) A cross section of anterior abdominal wall with a fascia defect causing hernia can be seen with muscle (red), fascia (black) and mesh (blue) labeled in different colors. (B) Inlay mesh implantation to fit in the gap created by the fascia and muscle defect. This method was largely abandoned due to high recurrence rates. (C) Onlay placement of mesh material to overlie and reinforce the fascia and muscle defect. (D) In the sublay technique mesh material is placed on a well vascularized wound bed underneath the muscle and it is also covered by two fascial layers.

This technique is considered the current gold standard with less complication and high success rates.

The POP occurs as a result of loss of support at three levels in the pelvis. Level I cardinal-uterosacral ligaments providing apical support, level II arcus tendineus fascia pelvis supporting middle part of vagina laterally and level III urogenital diaphragm and perineal body supporting lower part of the vagina [45]. The contribution of each of these structures to occurrence of prolapse as we see it in the clinic, is not well defined. A recent work, for example, suggests that lack of vaginal apical support was a significant contributor to the occurrence of anterior compartment In conclusion the use of mesh evolved over many years from an initial metal wire mesh to the monofilament, macroporous PPL mesh used in contemporary practice. Together with the improvements made in the surgical implantation technique mesh augmented surgical repairs now have very reasonable success rates in abdominal hernia surgeries. Although some of these improvements made to the material have been translated to the pelvic floor, we know that the same material when implanted vaginally to treat POP has resulted in unacceptably high complication rates.

This can be partially explained by factors related to the current surgical technique. The standard surgical technique, particularly those of transvaginal POP repairs, may need further improvements which will clearly require a better understanding of the pathophysiology of POP in women. Another important aspect is related to the pre and postoperative factors. It is now recognized that mesh augmented pelvic floor repair procedures, although conducted as minimally invasive day case procedures, involve placement of a permanent implant into the patients' body making post implantation surveillance necessary [12, 16]. Also factors related to patient selection, especially when the patients have co-morbidities such as diabetes and obesity, are known to influence postoperative outcomes. Surgeons' experience is another potentially important factor in the mesh implant procedures. Several recent consensus reports on how to control vaginal mesh related complications are now emphasizing that only surgeons/centers with subspecialist experience on implantation and postoperative management of patients with stress urinary incontinence and pelvic organ prolapse should undertake these procedures. Also the implementation of national mesh registries, thus not relying solely on the manufacturers to report mesh related adverse event and mandatory post-implantation surveillance systems are recommended.

**6.2. Defining the mechanical characteristics of the native human pelvic floor**

monly performed in these studies and it gives more reproducible results.

Our knowledge on the mechanical properties of the female pelvic floor mainly comes from mechanical testing of samples from the pelvic floor from human and animal samples. The availability of human samples for mechanical testing is often limited due to challenges and ethical concerns related to obtaining large tissue samples. Whole pelvic floor samples of animals that contain all the muscles and the connective tissues of the pelvic floor (e.g. 'vaginal supportive tissue complex') have been obtained from rats demonstrating that the ultimate failure in the testing protocol was due to a failure of paravaginal attachments [52]. Samples that only contain the connective tissues (e.g. fascia) have also been tested [53]. Disruption in the fascial structures is thought to be the main mechanism by which pelvic organ prolapse occurs [52].

Synthetic Materials Used in the Surgical Treatment of Pelvic Organ Prolapse: Problems…

http://dx.doi.org/10.5772/intechopen.76671

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Another factor limiting our ability to have robust definitions of mechanical properties of pelvic floor structures is the lack of standardized mechanical testing protocols for biological tissue samples. To obtain reproducible results when mechanically testing biological samples their unique organization, composition and *in vivo* functions need to be adopted to the mechanical testing protocols. Currently mechanical testing of samples from animal or human pelvic floor can mainly be tested by uniaxial and biaxial tensile testing. In uniaxial testing, the tissue to be tested is placed between two clamps (clamp-to-clamp testing) and a load is applied to the sample in one direction while observing for elongation/strain. Uniaxial testing is most com-

From a biomechanical point of view, the pelvic floor is a complex structure composed of active (e.g. muscles) and passive soft tissue (e.g. fascia) components attached to the pelvic bones all

**Figure 2.** Defining the basic mechanical properties of a material by uniaxial mechanical testing. The 'maximum load' is the maximum amount of stress that a material can bear before it fails. The 'maximum elongation' is the maximum strain a material can achieve before it fails. The 'yield strength' is where irreversible deformation to the material starts.
