Comparison of 2 single incision slings on the vagina in an ovine model
BACKGROUND: Stress urinary incontinence carries a significant healthcare burden for women worldwide. Single incision slings are minimally invasive mesh devices designed to treat stress urinary incontinence. For prolapse repair, meshes with higher porosity and lower structural stiffness have been associated with improved outcomes. OBJECTIVE: In this study, we compared the higher stiffness, lower porosity Altis sling with the lower stiffness, higher porosity Solyx sling in an ovine model. We hypothesized that SIS-B would have a negative impact on the host response. STUDY DESIGN: A total of Altis and Solyx single incision slings were implanted suburethrally into sheep according to the manufacturer's instructions on minimal tension. The mesh-urethral-vaginal complex and adjacent ungrafted vagina (no mesh control) were harvested en bloc at 3 months. Masson's trichrome and picrosirius red staining of 6 μm thin sections was performed to measure interfiber distance and tissue integration. Smooth muscle contractility to a 120 mM KCl stimulus was performed in an organ bath to measure myofiber-driven contractions. Standard biochemical assays were used to quantify glycosaminoglycan, total collagen, and elastin content, and collagen subtypes. Bending stiffness was performed in response to a uniaxial force to define susceptibility to folding / buckling. Statistical analysis was performed using Mann-Whitney, Gabriel's pairwise post hoc, Wilcoxon matched-pairs, and chi-square tests. RESULTS: The animals had similar ages (3-5 years), parity (multiparous), and weights (45-72 kg). Trichrome cross sections showed that the Altis sling buckled in a "C" or "S" shape in most samples (8 of 11), whereas buckling after Solyx sling implantation was observed in only a single sample (1 of 13; P = .004). Tissue integration, as measured by the presence of collagen or smooth muscle between the mesh fibers on trichrome 4× imaging, was increased in samples implanted with the Solyx sling compared with the Altis sling (P < .05). Total collagen content decreased significantly with both products when compared with the ungrafted vagina consistent with stress shielding. There was no difference in the 2 groups with regard to glycosaminoglycan or elastin content. The Altis sling mesh tissue complex demonstrated significantly higher amounts of both collagen types I and III than the Solyx sling-implanted tissue and the ungrafted control. Smooth muscle contractility in response to 120 mM KCl was decreased after implantation of both slings compared with the sham (P = .011 and P < .01), with no difference between mesh types (P = .099). Bending stiffness in the Altis sling was more than 4 times lower than in the Solyx, indicating an increased propensity to buckle (0.0186 vs 0.0883). CONCLUSION: The structurally stiffer Altis sling had decreased tissue integration and increased propensity to buckle after implantation. Increased collagen types I and III after the implantation of this device suggests that these changes may be associated with a fibrotic response. In contrast, the Solyx sling largely maintained a flat configuration and had improved tissue integration. The deformation of the Altis sling is not an intended effect and is likely caused by its lower bending stiffness. Both meshes induced a decrease in collagen content and smooth muscle contractility similar to previous findings for prolapse meshes and consistent with stress shielding. The long-term impact of buckling warrants further investigation.