title: An automated hand-held elastometer for quantifying the passive stiffness of the levator ani muscle in women.
abstract: OBJECTIVE
  Design and develop an automated, hand-held instrument (elastometer) to assess in vivo passive stiffness of the pelvic floor muscle.
  
  
  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.
  
  
  RESULTS
  The force-aperture spring measurements from the elastometer showed consistent (r(2) = 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Auckland Bioengineering Institute, The University of Auckland, Auckland, New Zealand.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Kruger
authors.forename: Poul M F
authors.initials: PM
authors.lastname: Nielsen
authors.forename: Stephanie C
authors.initials: SC
authors.lastname: Budgett
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Taberner
mesh_terms: D000328:Adult; D001331:Automation / Q000295:instrumentation* / Q000379:methods; D001696:Biomechanical Phenomena / Q000502:physiology; D004548:Elasticity / Q000502:physiology*; D004867:Equipment Design; D004864:Equipment and Supplies; D005260:Female; D006801:Humans; D009132:Muscles / Q000502:physiology*; D017773:Pelvic Floor / Q000502:physiology*; D015203:Reproducibility of Results; D016353:Self-Examination / Q000295:instrumentation* / Q000379:methods
keywords: avulsion; childbirth; levator ani muscles; passive stiffness; pelvic floor