An approach to evaluating and benchmarking the mechanical behavior of a surgical mesh prototype designed for the repair of abdominal wall defects.

Ventral hernia repair is a common surgical procedure in abdominal surgery in which surgical mesh has become an essential tool to improve outcomes. To avoid recurrences the mesh needs to mimic the mechanical behavior of the abdominal wall. In this scenario the mechanical properties at the interface between the mesh and its surrounding tissue is critical for the performance of the device and, therefore, the success after surgery. We aimed to characterize and compare the mechanical behavior of the patented prototype mesh Spider and four commercial meshes at the mesh-tissue interface. The prototype mesh was designed based on the hypothesis that the best performance for a large-sized defect in a ventral hernia is obtained when the mesh presents an isotropic behavior. In contrast, commercial meshes presented significant anisotropic behavior. Mechanical properties of the meshes were characterized through uniaxial tensile tests. Longitudinal and transverse axes were defined for each mesh, and samples were cut in each axis orientation. Samples underwent uniaxial tensile testing, from which the elastic modulus in each axis was determined. The degree of anisotropy was calculated as the ratio between the elastic modulus in each axis. An in silico model of the ventral hernia defect was designed to simulate the mesh-tissue interface behavior via finite element method. Meshes were modeled by an hyperelastic orthotropic constitutive model, which allowed isotropic symmetry as particular case for the prototype mesh. Abdominal wall was modeled using a Neo-Hookean model. Once the simulations were launched, mesh-tissue interface behavior was evaluated through the difference between Von Mises stress values on either size of the interface, both on the external and the internal face of the mesh and abdominal wall. Mechanical response was anisotropic for all commercial meshes and isotropic for the Spider prototype. Among commercial, Ultrapro® was highly anisotropic. Tests revealed Gore-Tex® to be the stiffest, followed by Repol Angimesh®, Spider and Ultrapro®; Duramesh™  was found to be the most compliant. Concerning mesh-tissue behavior, simulation results revealed the Spider prototype and Duramesh™  to be the best; Spider due to its uniformity and lower stress difference thanks to its nearly isotropic behavior, and Duramesh™  due to its compliant behavior. Our results suggest that the compromise between stiffness and anisotropy must be considered in order to improve the mechanical performance of the meshes, bearing in mind that for large-sized ventral defects, nearly isotropic mesh ensures better performance.

Necrotising fasciitis of the lower limb due to perforated inguinal hernia.

Acute inguinal hernia complications (incarceration, strangulation) are relatively frequent conditions, especially in the elderly. Urgent surgery is the appropriate treatment if manual reduction is not achieved or strangulation or perforation is suspected. We present a 77-year-old patient with necrotising fasciitis of the lower limb as a consequence of extraperitoneal perforation of a sliding inguinal hernia. This devastating condition was diagnosed 20 h after the manual reduction of the hernia. Suspicion arose at the physical examination (crepitation, signs of cellulitis) and clinical deterioration of the patient, and was confirmed by computed tomography (CT) scanning. Urgent surgery was performed, including sigmoidectomy, debridement of the necrotic tissues of the medial and anterior thigh compartment, and fasciectomy, combined with optimal intensive care support. No signs of peritoneal or pelvic involvement were found. However, the comorbidities, advanced age and the progression of the disease led to fatal outcome. Early recognition of the complications of strangulated hernias is of vital importance for successful treatment in these cases, even if no signs of acute abdomen are present.