A novel technique to measure in vivo uterine suspensory ligament stiffness

Abstract

Objective To describe a new computer-controlled research apparatus for measuring in vivo uterine ligament force-displacement behavior and stiffness and to present pilot data in women with and without prolapse. Study Design Seventeen women with varying uterine support underwent testing in the operating room (OR) after anesthetic induction. A tripod-mounted computer-controlled linear servoactuator was used to quantify force-displacement behavior of the cervix and supporting ligaments. The servoactuator applied a caudally-directed force to a tenaculum at 4 mm/s velocity until the traction force reached 17.8N (4 lbs.). Cervix location on POP-Q in clinic, in the OR at rest, and with minimal force (<1.1N), and maximum force (17.8N) was recorded. Ligament “stiffness” between minimum and maximum force was calculated. Results The mean (SD) subject age was 54.5 (12.7) years, parity 2.9 (1.1), BMI 29.0 (4.3) kg/m2, and POP-Q point C −3.1 (3.9) cm. POP-Q point C was most strongly correlated with cervix location at maximum force (r=+0.68, p=.003) and at rest (r=+0.62, p=.009). Associations between cervix location at minimum force (r=+0.46, p=.059) and ligament stiffness (r= −0.44,p=.079) were not statistically significant. Cervix location in the OR with minimal traction lay below the lowest point found on POP-Q for 13 women. Conclusions POP-Q point C was strongly correlated with cervix location at rest and at maximum traction force; however only 19% of the variation in POP-Q point C location was explained by ligament stiffness. The cervix location in the OR at minimal traction lay below POP-Q point C value in ¾ of women.

Traction force needed to reproduce physiologically observed uterine movement: technique development, feasibility assessment, and preliminary findings

“…Results from our physiologic testing suggest that apical ligament stiffness is not the primary factor contributing to uterine support. In a study by Smith et al, in vivo ligament stiffness only explained 19 % of the variation in POP-Q point C [4]. Therefore, when thinking about the etiology of apical support loss, we may presently have a tendency to overestimate the role of apical ligament stiffness and underestimate other important factors, such as ligament length.…”

“…The technique for making measurements of cervix location in the OR using a computer-controlled servoactuator device has been previously described [4] and is shown in Fig. 3.…”

“…For example, it is common to perform in vitro uniaxial tension tests on small excised pieces of the uterosacral ligaments and then calculate the tissue stress–strain curves [2, 3]. More recently, in vivo tests performed using cervical traction in the operating room (OR) resulted in force-displacement curves from which the stiffness of the cardinal and uterosacral ligament complexes were calculated [4, 5]. Whether either of these are physiologically relevant measures is unclear.…”

Mechanical Analysis of the Uterosacral Ligament: Swine vs. Human

“…While ex vivo studies have provided very valuable information with regards to the elastic and viscoelastic properties of the USL, in vivo mechanical tests of the USL, whenever possible, are ideal. 36,43 However, these tests can be conducted in humans only over a very short period of time due to ethical concerns associated with subjecting patients to mechanical testing for extended periods of time.…”

A multi-compartment 3-D finite element model of rectocele and its interaction with cystocele

“…The constitutive model was evaluated in Abaqus and the evaluation result showed that it was stable. The material properties values for the apical supports and uterine support tissues, which include a cardinal ligament (CL) and uterosacral ligament (USL) on each side of the vagina, were taken from our recent in vivo tissue tests (Luo et al, 2014b; Smith et al, 2013) on healthy women. In those studies we used a computer-controlled linear servo actuator to apply a continuous force and simultaneously recorded cervical displacement.…”