Exploring the basic science of prolapse meshes

Abstract

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.

FIGURE 1

Uniaxial tensile loading dramatically alters the pore size and pore geometries of nearly all mesh products. As shown, Gynemesh PS and UltraPro significantly deform at low loads (10 N). Macroscopically, the meshes undergo lateral contraction (Poisson’s effect). Microscopically pore dimensions are drastically reduced bringing filaments closer together. These behaviors are consistent with a markedly unstable geometry. In contrast, Restorelle (square pore) is stable, with minimal loss of porosity at 10 N [23^▪]. Adapted with permission from [23^▪].

FIGURE 2

Mesh vagina complex excised 3 months after insertion of mesh of identical dimensions in the primate by sacrocolpopexy. While Gynemesh PS buckles, laterally contracts and loses porosity when loaded, Restorelle (square pore) maintains its original flat conformation [28]. Adapted with permission from [28].

FIGURE 3

Immunofluorescent labeling of smooth muscle and in situ cell apoptosis in the vagina of rhesus macaque following the implantation of Gynemesh PS, UltroPro and Restorelle at 3 months. The red signal represents positive staining of α-SMA; the green signal represents apoptotic cells; the blue signal represents nuclei. S indicates the smooth muscle layer. ^* indicates the area of mesh fibers. The thickness of smooth muscle layer was significantly reduced in the Gynmesh PS group. In addition, following implantation with Gynemesh PS, the number of apoptotic cells was significantly increased in the subepithelium and adventitia compared to Sham and lower stiffness meshes, predominantly surrounding the mesh fibers. For the lower stiffness meshes, apoptotic cells were higher following implantation of UltraPro than Restorelle. Magnification: 100× [15]. Adapted with permission from [15].

FIGURE 4

Immunofluorescent labeling of pan-macrophage marker CD68 (red), M1 pro-inflammatory marker CD86 (orange), M2 pro-remodeling macrophage marker CD206 (green), and DAPI (blue). (a) a mesh-tissue section from a patient presenting with an exposure and implanted with the AMS Perigee prolapse mesh for 93 months; (b) a mesh-tissue section from a patient presenting with pain and implanted with the Gynecare TVT Secur for 6 months; (c) control tissue from patients without graft implantation. A predominance of pro-inflammatory M1 macrophages surround mesh fibers (^*) consistent with a prolonged immune response could be observed in both (a) and (b); however, this response is limited to the area immediately adjacent to mesh fibers. Control tissue contained few or no macrophages as compared to mesh patient tissue. Magnification 200× [16^▪]. Adapted with permission from [16^▪].