Biomechanical properties of human pelvic organs

To comparatively define the biomechanical characteristics of the pelvic organs (the vagina, bladder, and rectum), which are crucial for the maintenance of pelvic support. Despite minimal fundamental studies, meshes are increasingly implanted into the vesicovaginal and rectovaginal spaces to replace disrupted native tissues and to treat pelvic organ prolapse. However, the mechanical characteristics of these materials have not yet been compared with those of the "functional unit," the vagina, bladder, and rectum.

Samples from 5 fresh female cadavers without prolapse were collected. Uniaxial tension tests under monotonic and cyclic loading were performed and the stress-strain curves obtained.

The biomechanical properties of the vaginal, bladder, and rectal tissues differed significantly. We were able to demonstrate a nonlinear relationship between the stress and strain and a visco-hyperelastic behavior with a Mullins effect of damage of the tissues examined. Comparable rigidity was found between the investigated tissues at low strains; however, at large strain levels, marked differences could be observed. The vagina was much more rigid and less extendible than the rectal tissue, which, in turn, was more rigid than the bladder tissue. The anterior and posterior vagina revealed a different stiffness, and the bladder tissue was anisotropic at large strain levels.

Our results underline the pivotal role of the vaginal tissue for the maintenance of pelvic support. The observed differences with respect to tissue rigidity should have pronounced effects on the physiologic organ function, pointing to the necessity of a differentiated view on using the same prosthetic material for different anatomic locations.