Morphologic Evaluation of Post-implanted ...

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Gynecology SURGICAL TECHNOLOGY INTERNATIONAL XXVI

Morphologic Evaluation of Post-implanted Monofilament Polypropylene Mesh Utilizing a Novel Technique with Scanning Electron Microscopy Quantification ALI AZADI, MD, MSC ASSISTANT PROFESSOR NORTON WOMEN'S SPECIALISTS – UROGYNECOLOGY NORTON HEALTH CARE LOUISVILLE, KENTUCKY

ZHENMIN LEI, PHD ASSOCIATE PROFESSOR DEPARTMENT OF OBSTETRICS AND GYNECOLOGY UNIVERSITY OF LOUISVILLE SCHOOL OF MEDICINE LOUISVILLE, KENTUCKY JUN LIAO, PHD ASSOCIATE PROFESSOR DEPARTMENT OF BIOLOGICAL ENGINEERING MISSISSIPPI STATE UNIVERSITY MISSISSIPPI STATE, MISSISSIPPI

SOURAV S. PATNAIK, PHD RESEARCH ASSISTANT DEPARTMENT OF BIOLOGICAL ENGINEERING MISSISSIPPI STATE UNIVERSITY MISSISSIPPI STATE, MISSISSIPPI

NICOLETTE E. DEVENEAU, MD FELLOW OF FEMALE PELVIC MEDICINE AND RECONSTRUCTIVE SURGERY DEPARTMENT OF OBSTETRICS AND GYNECOLOGY UNIVERSITY OF LOUISVILLE SCHOOL OF MEDICINE LOUISVILLE, KENTUCKY

JACEK B. JASINSKI, PHD RESEARCH SCIENTIST CONN CENTER FOR RENEWABLE ENERGY RESEARCH UNIVERSITY OF LOUISVILLE LOUISVILLE, KENTUCKY

DONALD R. OSTERGARD, MD PROFESSOR-IN-RESIDENCE DIVISION OF FEMALE PELVIC MEDICINE AND RECONSTRUCTIVE SURGERY UNIVERSITY OF CALIFORNIA LOS ANGELES SCHOOL OF MEDICINE – HARBOR TORRANCE, CALIFORNIA

SEAN L. FRANCIS, MD ASSOCIATE PROFESSOR DEPARTMENT OF OBSTETRICS AND GYNECOLOGY UNIVERSITY OF LOUISVILLE SCHOOL OF MEDICINE LOUISVILLE, KENTUCKY

ABSTRACT

P

olypropylene mesh has been shown to shrink up to 50%; however, little is known about other changes that may occur while it is implanted. It is unclear whether such changes have clinical impact; nonetheless, knowledge of such can ultimately affect the technique of implantation and may affect

outcomes. The objective of this study was to evaluate surgically explanted mesh after two years implantation for evidence of change in morphology using scanning electron microscopy (SEM). Secondly, we -1-

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Morphologic Evaluation of Post-implanted Monofilament Polypropylene Mesh Utilizing a Novel Technique with Scanning Electron Microscopy Quantification AZADI/PATNAIK/JASINSKI/FRANCIS/LEI/LIAO/DEVENEAU/OSTERGARD

describe a novel technique for quantifying such changes with intentions for future validation. SEM imaging was conducted and mesh changes were visualized. SEM images revealed deep surface cracks both transverse and longitudinal, flaking and peeling of fibers, as well as fibrosis. Microstructural quantification of cracks was also completed. The fraction of transverse cracked area to whole surface area was 24.2%. Average crack length range was 0.58 to 71.46 µm and average crack thickness range was 0.99 to 25.46 µm. Polypropylene mesh is subject to structural changes after surgical implantation. It is important to investigate how these processes impact clinical outcomes. Validated techniques of quantifying such changes can prove useful in future research and aid in development of the ideal graft.

INTRODUCTION Pelvic floor dysfunction is a highly prevalent condition in the female population. Studies have estimated that American women have an 11% to 12% lifetime risk of undergoing an operation for pelvic organ prolapse (POP) or urinary incontinence (UI).1,2 Macroporous monofilament polypropylene mesh has been used in the repair of POP and UI and has gained increased popularity. In some studies, the use of mesh for treatment of pelvic organ prolapse has been shown to increase the anatomical success rate compared with native tissue repair.3,4 Polypropylene mesh is not inert after implantation in the body. Immediately after insertion, an acute inflammatory reaction begins. Neutrophils begin to produce oxidants; oxidation of the polypropylene chains produces free radicals, which cause various events, including depolymerization, cross-linking, oxidative degradation, additive leaching, hydrolysis, and stress cracking.5,6 These alterations in the chemical structure of polypropylene are responsible for visibly demonstrable fiber changes such as deep surface cracks, flaking, and peeling of the fibers.7 The processes noted have the potential to cause chronic inflammation, fibrosis, and mesh shrinkage that may lead to chronic pelvic pain. The objective of this study was to describe and characterize the microstructural morphologic changes

using specialized techniques with scanning electron microscopy (SEM). The secondary objective was to describe a novel technique for quantifying such changes with the intention of future validation. In this case, we show mesh degradation and excessive fibrotic tissue reaction in a sample of excised polypropylene mesh two years after implantation. The extent of mesh fiber damage was characterized by analyzing the microstructure of the cracks identified by SEM with image analysis tools including NIH ImageJ (U. S. National Institutes of Health, Bethesda, MD) and ImageAnalyzer (MeeSoft, Copenhagen, Denmark). CASE

CASE

A 72-year-old Caucasian female presented to the University of Louisville Female Pelvic Medicine and Reconstructive Surgery clinic for evaluation of pelvic pain and dyspareunia occurring after placement of anterior vaginal mesh (Uphold TM System, Boston Scientific, Natick, MA) that was placed for pelvic organ prolapse two years prior. Conservative treatments, including pelvic floor physical therapy, were unsuccessful. Pelvic examination did not show any obvious mesh erosion; however, there was a tight transverse band at the apex of the vagina that was tender to palpation and mimicked the pain she experienced with intercourse.

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Treatment options were discussed with the patient. After extensive counseling, she opted for segmental excision of the mesh body and arms. The patient proceeded to surgery for a vaginal excision of mesh. A vertical incision was made in the anterior vaginal wall extending to the apex of the vagina. The mesh was identified and dissected from surrounding tissue using a combination of sharp and blunt technique with care to avoid injury to adjacent organs. The body of the mesh and its arms were removed extending to the sacrospinous ligaments bilaterally. The mesh did not appear folded, rolled, or bunched at the time of surgical removal. At the completion of the removal, cystourethroscopy was performed to ensure integrity of the bladder and urethra. The patient had an uneventful postoperative course, and at two months following surgery she had no further pelvic pain or dyspareunia. METHODSMETHODS Immediately after excision, the mesh was placed in 4% paraformaldehyde fixative solution and kept at 4°C overnight. Under a dissecting microscope, tissue adherent to the mesh was cleared off as much as possible with care to avoid any physical damage to the mesh. The mesh was then rinsed three times with phosphate buffered saline, air dried, and prepared for SEM evaluation. The prepared samples were

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Gynecology SURGICAL TECHNOLOGY INTERNATIONAL XXVI

then placed on aluminum stubs using double-sided carbon tape. Samples were then sputter coated with gold using a SPI-MODULE Sputter CoaterÔ (Structure Probe, Inc, West Chester, PA). Samples were then viewed in an FEI Nova 600 high-resolution SEM (FEI CompanyÔ, Hillsboro, OR) with a filed-emission gun operating at the acceleration voltage of 10 kV. Images were assessed for structural changes in the mesh architecture. An image was then identified that showed the entire width of the mesh fiber and this image underwent further microstructural measurement (Fig. 1). Microstructural quantification of the cracks was done using NIH ImageJ (U. S. National Institutes of Health, Bethesda, MD) and ImageAnalyzer softwares (MeeSoft, Copenhagen, Denmark). Using NIH ImageJ, a region of interest (ROI) was selected from the original SEM image of the explanted mesh, then cropped into a smaller image and converted to binary format (Fig 2). Thresholding of the image using ImageAnalyzer software (MeeSoft, Copenhagen, Denmark) produced a white surface color and a dark crack appearance. The crack area percentage was calculated by normalizing the dark crack area to the total area of the cropped image. RESULTS RESULTS From the SEM images, we observed deep surface cracks and flaking and peeling of the mesh fibers (Fig. 1). There were noted to be both superficial and deep cracks in the mesh fibers as well as separation of outer layers from the inner mesh core (Figs. 1 & 3). Additionally, tissue fibrosis was observed around the mesh fibers as noted by the filamentous structures adherent to the mesh (Fig. 4). In the fibrotic areas there also appears to be folding of the polypropylene fibers (Fig 4). The compositions of the submicronic particles are unknown but are too small to be bacteria, which are about 1 micron in size (Fig 4). In addition to the dominant transverse cracks, the mesh fibers also showed longitudinal cracks (Fig. 3). Presence of longitudinal cracks in the mesh fibers is a unique observation in vaginal mesh, and only a handful of studies have reported similar findings.3,8,9 We found that almost one-fourth of

Figure 1. SEM images of explanted polypropylene mesh. A. Peeling of degraded outer layer of mesh fibers (arrow) at 500x magnification. B. Cracks in degraded fiber at 1500x magnification. C. Note the separation the outer degraded polypropylene layer (arrow) at 5,000x magnification. D. Deep cracks (arrow) at 20,000x magnification.

the mesh fiber surface consisted of cracks. From the microstructural quantifications, we found that the average crack length ranged from 0.58 µm to 71.46 µm, and average crack thickness ranged from 0.99 µm to 25.46 µm, with a mean crack area of 33.49 µm2. The fraction of the transverse cracked area to the whole surface was 24.2% as determined by the dark crack area to the total area of the cropped image (Fig. 2). The

frequency of transverse cracks per longitudinal length was found to be 7.7 objects per 10µm. DISCUSSION DISCUSSION Our case is an example of meshrelated complications in the female pelvic reconstructive surgery field, and

Figure 2. A. SEM image selected for further analysis and region of interest (ROI) (boxed). B. ROI was cropped from an original image and converted to binary format to quantify crack features.

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Morphologic Evaluation of Post-implanted Monofilament Polypropylene Mesh Utilizing a Novel Technique with Scanning Electron Microscopy Quantification AZADI/PATNAIK/JASINSKI/FRANCIS/LEI/LIAO/DEVENEAU/OSTERGARD

a tool to quantify the change. It is clear that polypropylene mesh is subject to structural changes after implantation, and further research is needed to assess how the changes affect clinical outcomes. CONCLUSION CONCLUSION Polypropylene mesh is subject to str uctural changes after surgical implantation. It is important to continue to investigate how these processes can impact clinical outcomes. Validated techniques of quantifying such changes can prove useful in future research and aid in development of the ideal graft and ideal placement technique. STI Figure 3. A. Cracks of degraded fiber at 1500x magnification. Longitudinal crack seen (arrow). B. Closer look at longitudinal crack (arrow). Note the area where part of the mesh on the outer surface of the fiber has been lost (starred area).

a unique description of the microstructural quantification of fiber cracks on degraded vaginal mesh explants. In this case study, we hypothesize that the mesh shrinkage and excessive fibrosis around it could be responsible for the patient’s symptoms of dyspareunia and pelvic pain. SEM images show strong tissue-mesh interactions including folding of the mesh fibers, indicating the body’s attempt to envelope the implant as a foreign body even after years of implantation. The presence of mesh cracking, even at two years out, shows that there are significant structural changes to the mesh. Our microstructural quantification analysis allowed us to show that a significant portion of the mesh was affected by cracking, which is unique to our study.

We hope to fur ther validate our microstructural quantification analysis with additional samples and use it to assess the extent of changes in mesh from other potentially damaging events. Concerns regarding mesh safety, as well as lack of level-1 evidence regarding efficacy, caused the release of a public warning by the United States Food and Drug Administration (FDA) and the United Kingdom’s National Institute for Health and Clinical Excellence (NICE). 10 A more complete knowledge of what happens to mesh and surrounding tissue after insertion will help us to understand and possibly prevent future complications. Our study provides further evidence and descriptions of these changes as well as

AUTHORS’ AUTHORS’DISCLOSURES DISCLOSURES Dr. Ostergard and Dr. Francis provide medicolegal consultations and testimony. All other authors have nothing to disclose. REFERENCES REFERENCES 1. Olsen AL, Smith VJ, Bergstrom JO, et al. Epidemiology of surgically managed pelvic organ prolapse and urinary incontinence. Obstet Gynecol 1997;89(4):501–6. 2. Fialkow MF, Newton KM, Lentz GM, et al. Lifetime risk of surgical management for pelvic organ prolapse or urinary incontinence. Int Urogunecol J Pel 2008;19(3):437–40. 3. Birch C. The use of prosthetics in pelvic reconstructive surgery. Best Pract Res Cl Ob 2005;19(6):979–91.

Figure 4. Excessive fibrosis around mesh sample. A. Note the distortion and folding of a polypropylene fiber (arrow) at 100x magnification. B. Fibrosis at 5000x magnification. C. Small particles close to the fibers and on the surface of the degraded mesh with 50,000x magnification.

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4. Maher C, Feiner B, Baessler K, et al. Surgical management of pelvic organ prolapse in women. Cochrane Database of Systematic Reviews 2013(4). doi:10.1002/14651858. CD004014.pub5. 5. Sternschuss G, Ostergard DR, Patel H. Post-implantation alterations of polypropylene in the human. J Urology 2012;188(1): 27–32. 6. Pierce LM, Rao A, Baumann SS, et al. Long-term histologic response to synthetic and biologic graft materials implanted in the

vagina and abdomen of a rabbit model. Am J Obstet Gynecol 2009;200(5):546.e1–8. 7. Clave A, Yahi H, Hammou JC, et al. Polypropylene as a reinforcement in pelvic surgery is not inert: comparative analysis of 100 explants. Int Urogynecol J 2010;21(3): 261–70. 8. Brun JL, Bordenave L, Lefebvre F, et al. Physical and biological characteristics of the main biomaterials used in pelvic surgery. BioMed Mater Eng 1992;2(4):203–25.

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9. Costello CR, Bachman SL, Ramshaw BJ, et al. Materials characterization of explanted polypropylene hernia meshes. J Biomed Mater R-A 2007;83(1):44–9. 10. Murphy M, Holzberg A, van Raalte H, et al. Time to rethink: an evidence-based response from pelvic surgeons to the FDA Safety Communication: UPDATE on Serious Complications Associated with Transvaginal Placement of Surgical Mesh for Pelvic Organ Prolapse. Int Urogynecol J 2012;23(1):5–9.