A novel technique to measure in vivo uterine suspensory ligament stiffness

Abstract

Objective: The purpose of this study was to describe a new computer-controlled research apparatus for measuring in vivo uterine ligament force-displacement behavior and stiffness and to present pilot data for 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/sec velocity until the traction force reached 17.8 N (4 lbs). Cervix location on Pelvic Organ Prolapse Quantification system (POP-Q) in the clinic, in the OR, at rest, and with minimal force (<1.1 N); maximum force (17.8 N) was recorded. Ligament "stiffness" between minimum and maximum force was calculated.

Results: The mean ± SD subject age was 54.5 ± 12.7 years; parity was 2.9 ± 1.1; body mass index was 29.0 ± 4.3 kg/m(2), and POP-Q point C was -3.1 ± 3.9 cm. POP-Q point C was correlated most strongly 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.

Conclusion: POP-Q point C was correlated strongly 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 three-fourths of the women.

Keywords: ligament stiffness; pelvic organ prolapse.