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.