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Levator bowl volume during straining and its relationship to other levator measures

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Abstract

Introduction and hypothesis

This study was aimed at measuring levator ani bowl volume at rest and while straining, comparing women with and without prolapse (controls), and assessing the ability of measures of the mid-sagittal bowl area, levator hiatus (LH), and urogenital hiatus (UGH) to predict bowl volume.

Methods

Forty MRI scans previously acquired in case-control prolapse studies, including 20 women with prolapse and 20 women without prolapse, of similar age and parity, were selected. 3D models of rest and strain bowl volumes were made using sagittal scans and 3D Slicer®. Mid-sagittal bowl area, UGH, and LH were measured using ImageJ. Data were analyzed using two sample t tests, effect sizes, and Pearson’s correlation coefficients at the 0.05 significance level.

Results

Data were acquired in a total of 40 total women. Levator bowl volume at strain had a correlation coefficient of 0.5 with bowl volume at rest. During straining, prolapse subjects had a 53% larger bowl volume than control subjects (254 ± 86 cm3 vs 166 ± 44 cm3, p < 0.001), but at rest, the difference was 34% (138 ± 40 cm3 vs 103 ± 25 cm3, p = 0.002). Effect sizes for all parameters were large (d > 0.75). The strongest correlation with straining bowl volume was mid-sagittal straining bowl area (r = 0.86), followed by LH strain (r = 0.80), then UGH strain (r = 0.76).

Conclusions

Straining levator bowl volume is substantially different than measures made at rest, with only a quarter of straining values explained by resting measurements. The bowl area at strain is the best 2D measurement estimating bowl volume and explains 74% of straining bowl volume.

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Acknowledgements

Supported by National Institutes of Health grants P50 HD044406 and R01 HD038665. The NIH did not play a role in the study design; in the collection, analysis, and interpretation of data; in the writing of the report; or in the decision to submit the article for publication.

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Authors and Affiliations

  1. School of Public Health, University of Michigan, Ann Arbor, MI, USA

    Lahari Nandikanti

  2. Department of Obstetrics & Gynecology, Rush University Medical Center, Chicago, IL, USA

    Anne G. Sammarco

  3. Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI, USA

    Luyun Chen & James A. Ashton-Miller

  4. Department of Obstetrics and Gynecology, University of Michigan, Ann Arbor, MI, USA

    John O. DeLancey

Authors
  1. Lahari Nandikanti
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  2. Anne G. Sammarco
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  3. Luyun Chen
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  4. James A. Ashton-Miller
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  5. John O. DeLancey
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Correspondence to John O. DeLancey.

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Appendix

Appendix

Table 4 Mean ± standard deviation for all measures
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Nandikanti, L., Sammarco, A.G., Chen, L. et al. Levator bowl volume during straining and its relationship to other levator measures. Int Urogynecol J 30, 1457–1463 (2019). https://doi.org/10.1007/s00192-019-04006-8

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  • DOI: https://doi.org/10.1007/s00192-019-04006-8

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