The impact of boundary conditions on surface curvature of polypropylene mesh in response to uniaxial loading

Profiling of the macrophage response to polypropylene mesh burden in vivo

Pelvic organ prolapse (POP) surgical repair with polypropylene mesh (PPM) offers improved anatomical outcomes compared to reconstruction using native tissue. However, PPM repair is hampered by complications, most commonly pain or mesh exposure, occurring in over 10 % of cases. This maladaptive response is, in part, attributed to the host response to a foreign material. Previous studies have demonstrated that mesh properties, such as weight, pore size, and porosity, influence downstream outcomes. In addition, computational models and in vivo mechanistic studies demonstrate that mesh deforms after tensioning in prolapse surgery resulting in collapsed pores and wrinkles. To further investigate the role of pore collapse in mesh complications, PPM was implanted flat, or in configurations that would deform upon tensioning in a POP repair surgery using a non-human primate model. After twelve weeks, we analyzed mesh-tissue complexes to characterize the overall host response, profile the macrophage response, and observe the influence of macrophages in downstream healing outcomes that may lead to complications. The results confirm that mesh deformations reproduce mesh exposure and thinning of vagina. In the PPM configurations with the greatest deformation, mesh burden was the highest, which resulted in an overall decrease in the number of cells within the implantation site. Among the cells that were present, we observed a predominance of M1 pro-inflammatory macrophages. While flat mesh was associated with an organized cellular response, deformed mesh led to an increasingly disorganized response as mesh burden increased. Nearly half of the responding macrophages expressed markers associated both with M1 and M2 phenotypes concurrently, suggesting the possibility of newly recruited macrophages responding even 12 weeks after implantation and/or a repetitive microinjury in which macrophages are continuously recruited and polarized without resolution of the host response. Biochemically, we observed a predominantly M1 pro-inflammatory signaling environment and decreased collagen content as a response to implanted mesh. This study evidences the importance of PPM mesh properties, which may alter mesh burden upon tensioning and impact downstream healing outcomes and emphasizes the need for devices that maintain their geometry following implantation in POP surgical repair.

Lengthwise regional mechanics of the human aneurysmal ascending thoracic aorta

The prognosis of patients undergoing emergency endovascular repair of ascending thoracic aortic aneurysm (ATAA) depends on defect location, with root disease bearing worse outcomes than proximal or distal aortopathy. We speculate that a spatial gradient in aneurysmal tissue mechanics through the length of the ascending thoracic aorta may fuel noted survival discrepancies. To this end, we performed planar biaxial testing on 153 root, proximal, and distal segments of ATAA samples collected from 80 patients receiving elective open surgical repair. Following data averaging via surface fitting-based interpolation of strain-controlled protocols, we combined in-vitro and in-vivo measurements of loads and geometry to resolve inflation-extension kinematics and evaluate mechanical metrics of stress, stiffness, and energy at consistent deformation levels. Representative (averaged) experimental data and simulated in-vivo conditions revealed significantly larger biaxial stiffness at the root compared to either proximal or distal tissues, which persisted as the entire aorta stiffened during aging. Advancing age further reduced biaxial stretch and energy storage, a measure of aortic function, across all ATAA segments. Importantly, age emerged as a stronger predictor of tissue mechanics in ATAA disease than either bicuspid aortic valve or connective tissue disorders. Besides strengthening the general understanding of aneurysmal disease, our findings provide specifications to customize the design of stent-grafts for the treatment of ATAA disease. Optimization of deployment and interaction of novel endovascular devices with the local native environment is expected to carry significant potential for improving clinical outcomes. STATEMENT OF SIGNIFICANCE: Elucidating the lengthwise regional mechanics of ascending thoracic aortic aneurysms (ATAAs) is critical for the design of endovascular devices tailored to the ascending aorta. Stent-grafts provide a less invasive alternative to support the long-term survival of ATAA patients ineligible for open surgical repair. In this study, we developed a numerical framework that combines semi-inverse constitutive and forward modeling with in-vitro and in-vivo data to extract mechanical descriptors of ATAA tissue behavior at physiologically meaningful deformation. Moving distally from the aortic root to the first ascending aortic branch, we observed a progressive decline in biaxial stiffness. Furthermore, we showed that aging leads to reduced aortic function and is a stronger predictor of mechanics than either valve morphology or underlying syndromic disorder.

Effect of gelatin methacryloyl hydrogel on healing of the guinea pig vaginal wall with or without mesh augmentation

INTRODUCTION AND HYPOTHESIS

The aims of this study were to evaluate the effectiveness of gelatin methacryloyl as an adjunct to anterior vaginal wall injury with or without vaginal mesh compared with traditional repair with suture.

METHODS

Virginal cycling Hartley strain guinea pigs (n = 60) were randomized to undergo surgical injury and repair using either polyglactin 910 suture or gelatin methacryloyl for epithelium re-approximation or anterior colporrhaphy with mesh augmentation using either polyglactin 910 suture or gelatin methacryloyl for mesh fixation and epithelium re-approximation. Noninjured controls (n = 5) were also evaluated. After 4 days, 4 weeks, or 3 months, tissues were analyzed by hematoxylin & eosin in addition to immunolabeling for macrophages, leukocytes, smooth muscle, and fibroblasts.

RESULTS

Surgical injury repaired with suture was associated with increased inflammation and vessel density compared with gelatin methacryloyl. Vimentin and α-smooth muscle actin expression were increased with gelatin methacryloyl at 4 days (p = 0.0026, p = 0.0272). There were no differences in changes in smooth muscle or overall histomorphology after 3 months between the two closure techniques. Mesh repair with suture was also associated with increased inflammation and vessel density relative to gelatin methacryloyl. Quantification of collagen content by picrosirius red staining revealed increased thick collagen fibers throughout the implanted mesh with gelatin methacryloyl compared with suture at 4 weeks (0.62 ± 0.01 μm2 vs 0.55 ± 0.01, p = 0.018). Even at the long-term time point of 3 months, mesh repair with suture resulted in a profibrotic encapsulation of the mesh fibers, which was minimal with gelatin methacryloyl. Smooth muscle density was suppressed after mesh implantation returning to baseline levels at 3 months regardless of fixation with suture or gelatin methacryloyl.

CONCLUSIONS

These results suggest that gelatin methacryloyl might be a safe alternative to suture for epithelium re-approximation and anchoring of prolapse meshes to the vagina and may improve chronic inflammation in the vaginal wall associated with mesh complications.

Mesh Deformation: a mechanism underlying polypropylene prolapse mesh complications in vivo

Polypropylene meshes used in pelvic organ prolapse (POP) repair are hampered by complications. Most POP meshes are highly unstable after tensioning ex vivo, as evidenced by marked deformations (pore collapse and wrinkling) that result in altered structural properties and material burden. By intentionally introducing collapsed pores and wrinkles into a mesh that normally has open pores and remains relatively flat after implantation, we reproduce mesh complications in vivo. To do this, meshes were implanted onto the vagina of rhesus macaques in nondeformed (flat) vs deformed (pore collapse +/- wrinkles) configurations and placed on tension. Twelve weeks later, animals with deformed meshes had two complications, 1) mesh exposure through the vaginal epithelium, and 2) myofibroblast proliferation with fibrosis - a mechanism of pain. The overarching response to deformed mesh was vaginal thinning associated with accelerated apoptosis, reduced collagen content, increased proteolysis, deterioration of mechanical integrity, and loss of contractile function consistent with stress shielding - a precursor to mesh exposure. Regional differences were observed, however, with some areas demonstrating myofibroblast proliferation and matrix deposition. Variable mechanical cues imposed by deformed meshes likely induce these two disparate responses. Utilizing meshes associated with uniform stresses on the vagina by remaining flat with open pores after tensioning is critical to improving outcomes. STATEMENT OF SIGNIFICANCE: Pain and exposure are the two most reported complications associated with the use of polypropylene mesh in urogynecologic procedures. Most meshes have unstable geometries as evidenced by pore collapse and wrinkling after tensioning ex vivo, recapitulating what is observed in meshes excised from women with complications in vivo. We demonstrate that collapsed pores and wrinkling results in two distinct responses 1) mesh exposure associated with tissue degradation and atrophy and 2) myofibroblast proliferation and matrix deposition consistent with fibrosis, a tissue response associated with pain. In conclusion, mesh deformation leads to areas of tissue degradation and myofibroblast proliferation, the likely mechanisms of mesh exposure and pain, respectively. These data corroborate that mesh implantation in a flat configuration with open pores is a critical factor for reducing complications in mesh-augmented surgeries.

Role of Fibroblasts and Myofibroblasts on the Pathogenesis and Treatment of Pelvic Organ Prolapse

Pelvic organ prolapse (POP) is a multifactorial connective tissue disorder caused by damage to the supportive structures of the pelvic floor, leading to the descent of pelvic organs in the vagina. In women with POP, fibroblast function is disturbed or altered, which causes impaired collagen metabolism that affects the mechanical properties of the tissue. Ideal surgical repair, either native tissue repair or POP surgery using an implant, aims to create a functional pelvic floor that is load-bearing, activating fibroblasts to regulate collagen metabolism without creating fibrotic tissue. Fibroblast function plays a crucial role in the pathophysiology of POP by directly affecting the connective tissue quality. On the other hand, fibroblasts determine the success of the POP treatment, as the fibroblast-to-(myo)fibroblast transition is the key event during wound healing and tissue repair. In this review, we aim to resolve the question of “cause and result” for the fibroblasts in the development and treatment of POP. This review may contribute to preventing the development and progress of anatomical abnormalities involved in POP and to optimizing surgical outcomes.

Design, mechanical and degradation requirements of biodegradable metal mesh for pelvic floor reconstruction

Pelvic organ prolapse (POP) is the herniation of surrounding tissue and organs into the vagina and or rectum, and is a result of weakening of pelvic floor muscles, connective tissue,...

A novel characterisation approach to reveal the mechano-chemical effects of oxidation and dynamic distension on polypropylene surgical mesh

Polypropylene (PP) surgical mesh, used successfully for the surgical repair of abdominal hernias, is associated with serious clinical complications when used in the pelvic floor for repair of stress urinary incontinence or support of pelvic organ prolapse. While manufacturers claim that the material is inert and non-degradable, there is a growing body of evidence that asserts PP fibres are subject to oxidative damage and indeed explanted material from patients suffering with clinical complications has shown some evidence of fibre cracking and oxidation. It has been proposed that a pathological cellular response to the surgical mesh contributes to the medical complications; however, the mechanisms that trigger the specific host response against the material are not well understood. Specifically, this study was constructed to investigate the mechano-chemical effects of oxidation and dynamic distension on polypropylene surgical mesh. To do this we used a novel advanced spectroscopical characterisation technique, secondary electron hyperspectral imaging (SEHI), which is based on the collection of secondary electron emission spectra in a scanning electron microscope (SEM) to reveal mechanical-chemical reactions within PP meshes.

A novel in vivo approach to assess strains of the human abdominal wall under known intraabdominal pressure

The study concerns mechanical behaviour of a living human abdominal wall. A better mechanical understanding of a human abdominal wall and recognition of its material properties is required to find mechanically compatible surgical meshes to significantly improve the treatment of ventral hernias. A non-invasive methodology, based on in vivo optical measurements is proposed to determine strains of abdominal wall corresponding to a known intraabdominal pressure. The measurement is performed in the course of a standard procedure of peritoneal dialysis. A dedicated experimental stand is designed for the experiment. The photogrammetric technique is employed to recover the three-dimensional surface geometry of the anterior abdominal wall at the initial and terminal instants of the dialysis. This corresponds to two deformation states, before and after filling the abdominal cavity with dialysis fluid. The study provides information on strain fields of living human abdominal wall. The inquiry is aimed at principal strains and their directions, observed at the level from -10% to 17%. The intraabdominal pressure related to the amount of introduced dialysis fluid measured within the medical procedure covers the range 11-18.5 cmH₂O. The methodology leads to the deformation state of the abdominal wall according to the corresponding loading conditions. Therefore, the study is a step towards an identification of mechanical properties of living human abdominal wall.

Novel Application of Photogrammetry to Quantify Fascicle Orientations of Female Cadaveric Pelvic Floor Muscles

Although critical for understanding and simulating pelvic floor muscle function and pathophysiology, the fascicle arrangements of the coccygeus and levator ani remain mostly undetermined. We performed close-range photogrammetry on cadaveric pelvic floor muscles to robustly quantify surface fascicle orientations. The pelvic floor muscles of 5 female cadavers were exposed through anatomic dissections, removed en bloc, and photographed from every required angle. Overlapping images were mapped onto in silico geometries and muscle fascicles were traced manually. Tangent vectors were calculated along each trace; interpolated to define continuous, 3D vector fields; and projected onto axial and sagittal planes to calculate angles with respect to the pubococcygeal line. Contralateral and ipsilateral pelvic floor muscles were compared within each donor (Kuiper's tests) and using mean values from all donors (William-Watsons tests). Contralateral muscles and all but one ipsilateral muscle pair differed significantly within each donor (p < 0.001). When mean values were considered collectively, no contralateral or ipsilateral statistical differences were found but all muscles compared differed by more than 10° on average. Close-range photogrammetry and subsequent analyses robustly quantified surface fascicle orientations of the pelvic floor muscles. The continuous, 3D vector fields provide data necessary for improving simulations of the female pelvic floor muscles.

Mechanical properties of warp-knitted hernia repair mesh with various boundary conditions

In this paper, two most representative hernia repair meshes were prepared with 0.15 mm polypropylene monofilaments via warp knitting technology, and their mechanical properties were tested in various aspects. Meanwhile, a focused investigation of the boundary conditions between the sutures and the mesh was simulated in several directions innovatively. The results revealed that the hernia repair mesh with different structures has different mechanical properties, and the mechanical properties of standard hernia repair mesh were superior to that of lightweight hernia repair mesh. In order to reduce foreign body sensation and postoperative adverse reactions significantly, the lightweight hernia repair mesh may be preferred. At the same time, the mesh should be placed in the proper direction to comply with the anisotropy of abdominal wall during operation. The area where the hernia mesh is in contact with the sutures was vulnerable to damage. The curved or wrinkled area of the hernia repair mesh increases with the increase of load, which may lead to poor tissue growth, a strong inflammatory response, and even the recurrence of the hernia. Therefore, the hernia repair meshes with different structures may require unique suture techniques. And they also should be further treated prior to implantation. This study provides a theoretical basis for development, utilization and improvement of meshes. Further research will focus on the biomechanical properties of the mesh after implantation in vivo studies.

Preventing Mesh Pore Collapse by Designing Mesh Pores With Auxetic Geometries: A Comprehensive Evaluation Via Computational Modeling

Pelvic organ prolapse (POP) meshes are exposed to predominately tensile loading conditions in vivo that can lead to pore collapse by 70-90%, decreasing overall porosity and providing a plausible mechanism for the contraction/shrinkage of mesh observed following implantation. To prevent pore collapse, we proposed to design synthetic meshes with a macrostructure that results in auxetic behavior, the pores expand laterally, instead of contracting when loaded. Such behavior can be achieved with a range of auxetic structures/geometries. This study utilized finite element analysis (FEA) to assess the behavior of mesh models with eight auxetic pore geometries subjected to uniaxial loading to evaluate their potential to allow for pore expansion while simultaneously providing resistance to tensile loading. Overall, substituting auxetic geometries for standard pore geometries yielded more pore expansion, but often at the expense of increased model elongation, with two of the eight auxetics not able to maintain pore expansion at higher levels of tension. Meshes with stable pore geometries that remain open with loading will afford the ingrowth of host tissue into the pores and improved integration of the mesh. Given the demonstrated ability of auxetic geometries to allow for pore size maintenance (and pore expansion), auxetically designed meshes have the potential to significantly impact surgical outcomes and decrease the likelihood of major mesh-related complications.

Mesh induced fibrosis: The protective role of T regulatory cells

Polypropylene mesh is widely used in urogynecologic surgery, but complications rates (pain and exposure) approach 10%. Emerging evidence implicates the adaptive immune system in regulating the foreign body response to mesh, particularly regulatory T cells (T_regs), which modify macrophage differentiation and down-regulate CD8⁺ effector T cells. We hypothesize that T_regs protect against a profibrotic response, a likely mechanism of pain complications. Here, thin sections of mesh-tissue complexes removed for the primary complaint of pain (N = 14) or exposure (N = 15) were labeled for CD8, CD4 (T_h), and FoxP3 (T_regs) via immunofluorescence. The same sections were analyzed for localized collagen deposition via a customized semi-quantitative assessment (0.25 mm² grid) after trichrome staining. TGF-β1 concentrations were determined by enzyme-linked immunosorbent assay. Fewer T_reg and CD4⁺ cells were found in fibrotic areas versus non-fibrotic areas (503 and 550/cm² fewer, respectively, both P < 0.001). TGF-β1 was higher in mesh samples compared to autologous control biopsies. TGF-β 1 inversely correlated with age, r -0.636(p = 0.008). No differences were found in T cell subgroups or fibrotic indices between pain and exposure groups. A moderate inverse relationship was found between TGF-β1 and T_regs (r -0.402, P = 0.009)_. T_regs were present up to 12 years after mesh implantation, challenging the assumption that the adaptive immune response to a foreign body is transient. In conclusion, the inverse relationship between fibrosis and T_regs, and TGF-β1 and T_regs points to a protective role of these cells. Similar immunologic responses in patients with pain and exposure suggest these complications exist along a spectrum. STATEMENT OF SIGNIFICANCE: The use of polypropylene mesh has been associated with improved outcomes in urogynecologic surgery, but is associated with significant complications, including pain and exposure through the vaginal epithelium. The host immune response features a prolonged inflammatory reaction containing innate immune cells and T lymphocytes clustered in capsules around the mesh fibers. This study uncovers the inverse relationship between T regulatory cells and the extent of fibrosis around the mesh, suggesting an anti-fibrotic effect. In addition, concentrations of T regulatory and T effector cells and levels of fibrosis connect these two most common complications into one mechanistic pathway. These new insights into the immune response to implanted mesh are an important step in understanding the causes of these surgical complications.

Mesh implants for hernia repair: an update

INTRODUCTION

Today the use of textile meshes has become a standard for the treatment of abdominal wall hernias and for the reinforcement of any tissue repair as the strength of the implant decreases the recurrence rates. With increasing use, side effects of the textile implants became apparent, as well.

AREAS COVERED

Based on publications in Medline over the past decade, general and specific benefits, as well as risks, are discussed with the challenge to define individual risk-benefit ratios. For meshes, certain high-risk or low-risk conditions can be defined. In an attempt to eliminate mesh-related risks, quality control for medical devices has meanwhile been revised. In both the USA and the EU post-market surveillance studies are required to keep medical devices approved.

EXPERT COMMENTARY

The impact of material on the complication rate will vary depending on the patient's co-morbidity or the risks of the procedure. Even the best material can end up with disappointing results in case of poor healing or poor surgery. On the other hand, when using high-risk devices, most of the complications after excellent surgery with excellent indication can be supposed to be mesh-related. Thus, the use of low-risk devices is recommended even though its advantage may not be demonstrable in clinical studies.

Transvaginal treatment of anterior and apical genital prolapses using an Ultra lightweight mesh: Restorelle® Direct Fix™. A retrospective study on feasibility and morbidity

BACKGROUND

Vaginal mesh safety information is limited, especially concerning single incision techniques using ultra lightweight meshes for the treatment of anterior pelvic organ prolapse (POP).

OBJECTIVE

To determine the intraoperative and postoperative complication rates after anterior POP repair involving an ultralight mesh (19g/m²): Restorelle^® Direct Fix™.

METHODS

A case series of 218 consecutive patients, operated on between January 2013 and December 2016 in ten tertiary and secondary care centres, was retrospectively analyzed. Eligible patients had POP vaginal repair (recurrent or not) planned with anterior Restorelle^® Direct Fix™ mesh (with or without posterior mesh). Surgical complications were graded using the Clavien-Dindo classification.

RESULTS

Intraoperative complications were bladder wound (0.5%), rectal wound (0.5%), ureteral injuries (0.9%). 98.2% of the patient did not have per operative complications. We observed one fail of procedure. Early complications mainly included urinary retention (8.7%) urinary tract infections (5.5%) and haematoma (2.7%). One haematoma required surgical treatment and another, embolization. 80.7% of the patient did not have complications during hospitalization and 80.3% did not have complication at the follow up visit. None of the analyzed factors (age, body mass index, surgical history, grade of prolapse or concomitant procedure) was significantly associated with the risk of perioperative complications. A total of 2.8% patients had grade III complications according Clavien Dindo. None had grade IV or V.

CONCLUSIONS

This multicentre case-series on the early experience of the use of anterior Restorelle^® Direct Fix™ mesh showed a satisfactory technical feasibility and a low rate of grade III complications according Clavien Dindo. Long term studies are necessary to assess anterior Restorelle^® Direct Fix™ mesh performances and to appraise patient satisfaction feedback.

Modern Theories of Pelvic Floor Support : A Topical Review of Modern Studies on Structural and Functional Pelvic Floor Support from Medical Imaging, Computational Modeling, and Electromyographic Perspectives

PURPOSE OF REVIEW

Weakened pelvic floor support is believed to be the main cause of various pelvic floor disorders. Modern theories of pelvic floor support stress on the structural and functional integrity of multiple structures and their interplay to maintain normal pelvic floor functions. Connective tissues provide passive pelvic floor support while pelvic floor muscles provide active support through voluntary contraction. Advanced modern medical technologies allow us to comprehensively and thoroughly evaluate the interaction of supporting structures and assess both active and passive support functions. The pathophysiology of various pelvic floor disorders associated with pelvic floor weakness is now under scrutiny from the combination of (1) morphological, (2) dynamic (through computational modeling), and (3) neurophysiological perspectives. This topical review aims to update newly emerged studies assessing pelvic floor support function among these three categories.

RECENT FINDINGS

A literature search was performed with emphasis on (1) medical imaging studies that assess pelvic floor muscle architecture, (2) subject-specific computational modeling studies that address new topics such as modeling muscle contractions, and (3) pelvic floor neurophysiology studies that report novel devices or findings such as high-density surface electromyography techniques. We found that recent computational modeling studies are featured with more realistic soft tissue constitutive models (e.g., active muscle contraction) as well as an increasing interest in simulating surgical interventions (e.g., artificial sphincter). Diffusion tensor imaging provides a useful non-invasive tool to characterize pelvic floor muscles at the microstructural level, which can be potentially used to improve the accuracy of the simulation of muscle contraction. Studies using high-density surface electromyography anal and vaginal probes on large patient cohorts have been recently reported. Influences of vaginal delivery on the distribution of innervation zones of pelvic floor muscles are clarified, providing useful guidance for a better protection of women during delivery. We are now in a period of transition to advanced diagnostic and predictive pelvic floor medicine. Our findings highlight the application of diffusion tensor imaging, computational models with consideration of active pelvic floor muscle contraction, high-density surface electromyography, and their potential integration, as tools to push the boundary of our knowledge in pelvic floor support and better shape current clinical practice.

Exploring the basic science of prolapse meshes

PURPOSE OF REVIEW

Polypropylene mesh has been widely used in the surgical repair of pelvic organ prolapse. However, low but persistent rates of complications related to mesh, most commonly mesh exposure and pain, have hampered its use. Complications are higher following transvaginal implantation prompting the Food and Drug Administration to release two public health notifications warning of complications associated with transvaginal mesh use (PHN 2008 and 2011) and to upclassify transvaginal prolapse meshes from Class II to Class III devices. Although there have been numerous studies to determine the incidence and management of mesh complications as well as impact on quality of life, few studies have focused on mechanisms.

RECENT FINDINGS

In this review, we summarize the current understanding of how mesh textile properties and mechanical behavior impact vaginal structure and function, as well as the local immune response. We also discuss how mesh properties change in response to loading.

SUMMARY

We highlight a few areas of current and future research to emphasize collaborative strategies that incorporate basic science research to improve patient outcomes.

International guidelines for groin hernia management

INTRODUCTION

Worldwide, more than 20 million patients undergo groin hernia repair annually. The many different approaches, treatment indications and a significant array of techniques for groin hernia repair warrant guidelines to standardize care, minimize complications, and improve results. The main goal of these guidelines is to improve patient outcomes, specifically to decrease recurrence rates and reduce chronic pain, the most frequent problems following groin hernia repair. They have been endorsed by all five continental hernia societies, the International Endo Hernia Society and the European Association for Endoscopic Surgery.

METHODS

An expert group of international surgeons (the HerniaSurge Group) and one anesthesiologist pain expert was formed. The group consisted of members from all continents with specific experience in hernia-related research. Care was taken to include surgeons who perform different types of repair and had preferably performed research on groin hernia surgery. During the Group's first meeting, evidence-based medicine (EBM) training occurred and 166 key questions (KQ) were formulated. EBM rules were followed in complete literature searches (including a complete search by The Dutch Cochrane database) to January 1, 2015 and to July 1, 2015 for level 1 publications. The articles were scored by teams of two or three according to Oxford, SIGN and Grade methodologies. During five 2-day meetings, results were discussed with the working group members leading to 136 statements and 88 recommendations. Recommendations were graded as "strong" (recommendations) or "weak" (suggestions) and by consensus in some cases upgraded. In the Results and summary section below, the term "should" refers to a recommendation. The AGREE II instrument was used to validate the guidelines. An external review was performed by three international experts. They recommended the guidelines with high scores. The risk factors for inguinal hernia (IH) include: family history, previous contra-lateral hernia, male gender, age, abnormal collagen metabolism, prostatectomy, and low body mass index. Peri-operative risk factors for recurrence include poor surgical techniques, low surgical volumes, surgical inexperience and local anesthesia. These should be considered when treating IH patients. IH diagnosis can be confirmed by physical examination alone in the vast majority of patients with appropriate signs and symptoms. Rarely, ultrasound is necessary. Less commonly still, a dynamic MRI or CT scan or herniography may be needed. The EHS classification system is suggested to stratify IH patients for tailored treatment, research and audit. Symptomatic groin hernias should be treated surgically. Asymptomatic or minimally symptomatic male IH patients may be managed with "watchful waiting" since their risk of hernia-related emergencies is low. The majority of these individuals will eventually require surgery; therefore, surgical risks and the watchful waiting strategy should be discussed with patients. Surgical treatment should be tailored to the surgeon's expertise, patient- and hernia-related characteristics and local/national resources. Furthermore, patient health-related, life style and social factors should all influence the shared decision-making process leading up to hernia management. Mesh repair is recommended as first choice, either by an open procedure or a laparo-endoscopic repair technique. One standard repair technique for all groin hernias does not exist. It is recommended that surgeons/surgical services provide both anterior and posterior approach options. Lichtenstein and laparo-endoscopic repair are best evaluated. Many other techniques need further evaluation. Provided that resources and expertise are available, laparo-endoscopic techniques have faster recovery times, lower chronic pain risk and are cost effective. There is discussion concerning laparo-endoscopic management of potential bilateral hernias (occult hernia issue). After patient consent, during TAPP, the contra-lateral side should be inspected. This is not suggested during unilateral TEP repair. After appropriate discussions with patients concerning results tissue repair (first choice is the Shouldice technique) can be offered. Day surgery is recommended for the majority of groin hernia repair provided aftercare is organized. Surgeons should be aware of the intrinsic characteristics of the meshes they use. Use of so-called low-weight mesh may have slight short-term benefits like reduced postoperative pain and shorter convalescence, but are not associated with better longer-term outcomes like recurrence and chronic pain. Mesh selection on weight alone is not recommended. The incidence of erosion seems higher with plug versus flat mesh. It is suggested not to use plug repair techniques. The use of other implants to replace the standard flat mesh in the Lichtenstein technique is currently not recommended. In almost all cases, mesh fixation in TEP is unnecessary. In both TEP and TAPP it is recommended to fix mesh in M3 hernias (large medial) to reduce recurrence risk. Antibiotic prophylaxis in average-risk patients in low-risk environments is not recommended in open surgery. In laparo-endoscopic repair it is never recommended. Local anesthesia in open repair has many advantages, and its use is recommended provided the surgeon is experienced in this technique. General anesthesia is suggested over regional in patients aged 65 and older as it might be associated with fewer complications like myocardial infarction, pneumonia and thromboembolism. Perioperative field blocks and/or subfascial/subcutaneous infiltrations are recommended in all cases of open repair. Patients are recommended to resume normal activities without restrictions as soon as they feel comfortable. Provided expertise is available, it is suggested that women with groin hernias undergo laparo-endoscopic repair in order to decrease the risk of chronic pain and avoid missing a femoral hernia. Watchful waiting is suggested in pregnant women as groin swelling most often consists of self-limited round ligament varicosities. Timely mesh repair by a laparo-endoscopic approach is suggested for femoral hernias provided expertise is available. All complications of groin hernia management are discussed in an extensive chapter on the topic. Overall, the incidence of clinically significant chronic pain is in the 10-12% range, decreasing over time. Debilitating chronic pain affecting normal daily activities or work ranges from 0.5 to 6%. Chronic postoperative inguinal pain (CPIP) is defined as bothersome moderate pain impacting daily activities lasting at least 3 months postoperatively and decreasing over time. CPIP risk factors include: young age, female gender, high preoperative pain, early high postoperative pain, recurrent hernia and open repair. For CPIP the focus should be on nerve recognition in open surgery and, in selected cases, prophylactic pragmatic nerve resection (planned resection is not suggested). It is suggested that CPIP management be performed by multi-disciplinary teams. It is also suggested that CPIP be managed by a combination of pharmacological and interventional measures and, if this is unsuccessful, followed by, in selected cases (triple) neurectomy and (in selected cases) mesh removal. For recurrent hernia after anterior repair, posterior repair is recommended. If recurrence occurs after a posterior repair, an anterior repair is recommended. After a failed anterior and posterior approach, management by a specialist hernia surgeon is recommended. Risk factors for hernia incarceration/strangulation include: female gender, femoral hernia and a history of hospitalization related to groin hernia. It is suggested that treatment of emergencies be tailored according to patient- and hernia-related factors, local expertise and resources. Learning curves vary between different techniques. Probably about 100 supervised laparo-endoscopic repairs are needed to achieve the same results as open mesh surgery like Lichtenstein. It is suggested that case load per surgeon is more important than center volume. It is recommended that minimum requirements be developed to certify individuals as expert hernia surgeon. The same is true for the designation "Hernia Center". From a cost-effectiveness perspective, day-case laparoscopic IH repair with minimal use of disposables is recommended. The development and implementation of national groin hernia registries in every country (or region, in the case of small country populations) is suggested. They should include patient follow-up data and account for local healthcare structures. A dissemination and implementation plan of the guidelines will be developed by global (HerniaSurge), regional (international societies) and local (national chapters) initiatives through internet websites, social media and smartphone apps. An overarching plan to improve access to safe IH surgery in low-resource settings (LRSs) is needed. It is suggested that this plan contains simple guidelines and a sustainability strategy, independent of international aid. It is suggested that in LRSs the focus be on performing high-volume Lichtenstein repair under local anesthesia using low-cost mesh. Three chapters discuss future research, guidelines for general practitioners and guidelines for patients.

CONCLUSIONS

The HerniaSurge Group has developed these extensive and inclusive guidelines for the management of adult groin hernia patients. It is hoped that they will lead to better outcomes for groin hernia patients wherever they live. More knowledge, better training, national audit and specialization in groin hernia management will standardize care for these patients, lead to more effective and efficient healthcare and provide direction for future research.

On the Stiffness of the Mesh and Urethral Mobility: A Finite Element Analysis

Midurethral slings are used to correct urethral hypermobility in female stress urinary incontinence (SUI), defined as the complaint of involuntary urine leakage when the intra-abdominal pressure (IAP) is increased. Structural and thermal features influence their mechanical properties, which may explain postoperative complications, e.g., erosion and urethral obstruction. We studied the effect of the mesh stiffness on urethral mobility at Valsalva maneuver, under impairment of the supporting structures (levator ani and/or ligaments), by using a numerical model. For that purpose, we modeled a sling with “lower” versus “higher” stiffness and evaluated the mobility of the bladder and urethra, that of the urethrovesical junction (the α-angle), and the force exerted at the fixation of the sling. The effect of impaired levator ani or pubourethral ligaments (PUL) alone on the organs displacement and α-angle opening was similar, showing their important role together on urethral stabilization. When the levator ani and all the ligaments were simulated as impaired, the descent of the bladder and urethra went up to 25.02 mm, that of the bladder neck was 14.57 mm, and the α-angle was 129.7 deg, in the range of what was found in women with SUI. Both meshes allowed returning to normal positioning, although at the cost of higher force exerted by the mesh with higher stiffness (3.4 N against 2.3 N), which can relate to tissue erosion. This finite element analysis allowed mimicking the biomechanical response of the pelvic structures in response to changing a material property of the midurethral synthetic mesh.

Mobility and stress analysis of different surgical simulations during a sacral colpopexy, using a finite element model of the pelvic system

INTRODUCTION AND HYPOTHESIS

We aim to analyze the combined influence of the size of the mesh, the number of sutures, the combined use of an anterior and posterior mesh, and the tension applied to the promontory, on the mobility of the pelvic organs and on the sutures, using a Finite Element (FE) model of the female pelvic system during abdominal sacral colpopexy.

METHODS

We used a FE model of the female pelvic system, which allowed us to simulate the mobility of the pelvic system and to evaluate problems related to female prolapse. The meshes were added to the geometrical model and then transferred to computing software. This analysis allowed us to compare the stress and mobility during a thrust effort in different situations.

RESULTS

The bigger the mesh, the less mobility of both anterior and posterior organs there would be. This is accompanied by an increase in stress at the suture level. The combination of a posterior mesh with an anterior one decreases mobility and stress at the suture level. There is a particularly relevant stressing zone on the suture at the cervix. The increase in the number of sutures induces a decrease in the tension applied at each suture zone and has no impact on organ mobility.

CONCLUSION

Our model enables us to simulate and analyze an infinite number of surgical hypotheses. Even if these results are not validated at a clinical level, we can observe the importance of the association of both an anterior and a posterior mesh or the number of sutures.