In-plane and out-of-plane deformations of gilt utero-sacral ligaments

The uterosacral ligaments (USLs) are supportive structures of the uterus and apical vagina. The mechanical function of these ligaments within the pelvic floor is crucial not only in normal physiological conditions but also in reconstructive surgeries for pelvic organ prolapse. Discrepancies in their anatomical and histological description exist in the literature, but such discrepancies are likely due to large variations of these structures. This makes mechanical testing very challenging, requiring the development of advanced methods for characterizing their mechanical properties. This study proposes the use of planar biaxial testing, digital image correlation (DIC), and optical coherence tomography (OCT) to quantify the deformations of the USLs, both in-plane and out-of-plane. Using the gilts as an animal model, the USLs were found to deform significantly less in their main direction (MD) of in vivo loading than in the direction perpendicular to it (PD) at increasing equibiaxial stresses. Under constant equibiaxial loading, the USLs deform over time equally, at comparable rates in both the MD and PD. The thickness of the USLs decreases as the equibiaxial loading increases but, under constant equibiaxial loading, the thickness increases in some specimens and decreases in others. These findings could contribute to the design of new mesh materials that augment the support function of USLs as well as noninvasive diagnostic tools for evaluating the integrity of the USLs.