Biomechanical compatibility of surgical mesh and fascia being reinforced: dependence of experimental hernia defect repair results on anisotropic surgical mesh positioning.

PURPOSE: We aimed to compare the effectiveness of experimental middle hernia defect repair in regard to the transverse and longitudinal positioning of anisotropic lightweight surgical mesh.
METHODS: The mechanical properties of fascial layers and surgical mesh DynaMesh(®)-PP Light were determined in two perpendicular directions under uniaxial tension. In 12 male Wistar rats, middle hernia defect was repaired by the sublay technique. In six animals, the mesh was positioned across (DLH group) and in the other six along (DLV group) the midline. At 6 months after implantation, mesh deformation, structural rearrangement, and repaired abdominal wall biomechanics were evaluated. Histological sections were stained with van Giesen and Mallory's trichrome.
RESULTS: The anisotropic mechanical properties of the mesh and fascial layers coincided in the DLH group, but did not correspond to each other in the DLV group. In the DLV group, meshes were stretched in width by 11.4% and reduced in length by 12.7%. In all animals, the lower edge of the mesh was shifted to a defect area with margin hernia formation in two rats. Constant shear stress caused disproportional connective tissue formation. Repaired abdominal wall lost its natural elasticity. In the DLH group, the mesh deformation was minimal. Formed connective tissue was tightly associated with the anterior layer and did not differ from it in composition. The mechanical properties of repaired abdominal wall were close to those of the anterior layer.
CONCLUSIONS: In prosthetic hernia repair, the mechanical properties of surgical mesh should correspond with those of the fascia being repaired. A mismatch of mechanical properties may result in implant deformation, abdominal wall biomechanics impairment, and recurrent herniation at the edges of the meshes.