An automated hand-held elastometer for quantifying the passive stiffness of the levator ani muscle in women


  • Heinz Koelbl led the peer-review process as the Associate Editor responsible for the paper.
  • Conflict of interest: none.



Design and develop an automated, hand-held instrument (elastometer) to assess in vivo passive stiffness of the pelvic floor muscle.

Materials and Methods

The elastometer system consisted of a hand piece, real-time controller, and laptop computer. A cable connected the hand-piece to the controller, which communicated with a laptop computer via an ethernet connection. Force sensitivity calibration and displacement accuracy were determined experimentally using a spring load and an Instron mechanical tester. A test re-test series quantified the in vivo repeatability (within a procedure) and reproducibility (between procedures after a 5 min delay) of passive stiffness in volunteers (n = 20). Stiffness was determined from the gradient of the force–displacement curve for each cycle.


The force-aperture spring measurements from the elastometer showed consistent (r2 = 1.0000) agreement with those measured by the Instron. The difference between spring stiffness as measured by the elastometer and the Instron (388.1 N/m cf. 388.5 N/m, respectively) was negligible. The intra-class correlation coefficient for repeatability within procedures was 0.986 95% CI (0.964–0.994) n = 20, and reproducibility between procedures ICC 0.934 (95% CI 0.779–0.981) n = 12. Bland–Altman analysis determined a bias of 0.3 and 18.5 N/m, for repeatability and reproducibility respectively. Neither bias is likely to be clinically significance.


The elastometer demonstrated very good repeatability and accuracy in the measurement of force/displacement during in vitro testing. There was a high degree of repeatability and reproducibility in stiffness measurements in a test re-test series. Our results demonstrate the elastometer is accurate and reliable and thereby suitable for larger clinical trials. Neurourol. Urodynam. 34:133–138, 2015. © 2013 Wiley Periodicals, Inc.