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:TMfor both treatment groups was greater than Pbo for strains from 0% to 12% (P < .04). (2) RL:TMfor 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.