Mechanical properties of pelvic soft tissue of young women and impact of aging.

INTRODUCTION AND HYPOTHESIS: The female pelvic floor is a complex network of ligaments and muscles whose mechanical properties have not been completely understood. The goal of this study is to understand the biomechanical properties of the pelvic floor tissues of young women and the impact of aging. METHODS: Biomechanical uniaxial tension tests were performed on pelvic floor tissues (ligaments and organs) of six young female cadavers (average 29 years old). Results have been analyzed in order to define the characteristics of the mechanical properties of young pelvic soft tissues. Results have been compared with those in the literature in order to understand the similarities and discrepancies between young and old patients. RESULTS: Damageable, nonlinear elastic biomechanical behavior is observed. The variation in stiffness among the pelvic floor organs could be shown. Ligaments and the vaginal wall are the most rigid organs, whereas the rectum and bladder tend to be less rigid (approximately two times less rigid for small deformations and three times less rigid for large deformations). This study shows that ligaments and the vaginal wall of young women have similar mechanical behavior while those of older women differ. Furthermore, young women's tissues differ slightly from older women's tissues. CONCLUSIONS: Results show that aging and possibly diverse "trauma" have an impact on modifying the mechanical behavior of pelvic floor tissues. Over time pelvic floor ligaments and vaginal tissues will differentiate and acquire different mechanical behavior, as seen within the literature in older cadavers.

Comparative analysis of pelvic ligaments: a biomechanics study.

INTRODUCTION AND HYPOTHESIS: Pelvic organ prolapse (POP) affects one third of women of all ages and is a major concern for gynecological surgeons. In pelvic reconstructive surgery, native ligaments are widely used as a corrective support, while their biomechanical properties are unknown. We hypothesized differences in the strength of various pelvic ligaments and therefore, aimed to evaluate and compare their biomechanical properties. MATERIALS AND METHODS: Samples from the left and right broad, round, and uterosacral ligaments from 13 fresh female cadavers without pelvic organ prolapse were collected. Uniaxial tension tests at a constant rate of deformation were performed and stress-strain curves were obtained. RESULTS: We observed a non-linear stress-strain relationship and a hyperelastic mechanical behavior of the tissues. The uterosacral ligaments were the most rigid whether at low or high deformation, while the round ligament was more rigid than the broad ligament. CONCLUSION: Pelvic ligaments differ in their biomechanical properties and there is fairly good evidence that the uterosacral ligaments play an important role in the maintenance of pelvic support from a biomechanical point of view.

The effects of hormone replacement on the biomechanical properties of the uterosacral and round ligaments in the monkey model.

OBJECTIVE: The purpose of this study was to determine effects of ovariectomy (OVX) and conjugated equine estrogens plus medroxyprogesterone acetate (CEE/MPA), or ethinyl estradiol plus norethindrone acetate (EE/NA) on biomechanics of uterosacral (USL) and round (RL) ligaments in postmenopausal (PMP) monkeys. STUDY DESIGN: This was a randomized, triple blind, placebo-controlled study. OVX monkeys received 12 months no treatment (Pbo) (n = 19), CEE/MPA (n = 19), or EE/NA (n = 21). USL and RL step strains and stress-relaxation data were curve-fitted, giving strain-dependent tensile modulus (TM) from 0% to 30%. RESULTS: (1) USL: TM for both treatment groups was greater than Pbo for strains from 0% to 12% (P < .04). (2) RL: TM for both treatment groups was smaller than Pbo for strains from 12% to 30% (P < .05). No differences were found between treatment regimens. CONCLUSION: CEE/MPA and EE/NA both affect functional biomechanical properties by increasing tensile stiffness in the USL and decreasing it in the RL.

Smooth muscle fraction of the round ligament in women with pelvic organ prolapse: a computer-based morphometric analysis.

Our objective was to compare the collagen and muscle content of the round ligament of uteri in women with pelvic organ prolapse. We evaluated the tissue samples obtained from the round ligaments of 22 patients with uterine prolapse who underwent vaginal hysterectomy (group A, study) and from 26 patients with no pelvic relaxation in whom total abdominal hysterectomy was performed for benign reasons (group B, controls). Morphometric analysis was performed on histologic cross-sections of the round ligament. Sections from each sample were stained with hematoxylin and eosin and Masson's trichrome methods. A computer system was used for morphometric measurements. We used independent samples t-test or Mann-Whitney U test to investigate the difference between the two groups. It was found that the smooth muscle fraction of the round ligament in women with uterine prolapse was significantly decreased compared with that of healthy control subjects and concluded that decreased smooth muscle content may be an important pathogenetic factor in uterine prolapse.