Mesh deformation: A mechanism underlying polypropylene prolapse mesh complications in vivo

Abstract

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 result 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.

Keywords: Biomechanical properties; Extracellular matrix; Stress shielding; Synthetic mesh complications; Vagina.