Effects of Levator Ani Muscle Morphology on the Mechanics of Vaginal Childbirth

  • Xiani Yan
  • Jennifer A. Kruger
  • Martyn P. Nash
  • Poul M. F. Nielsen
Conference paper


Childbirth-induced trauma is one of the leading factors that cause pelvic floor (PF) muscle dysfunction. There is preliminary evidence to suggest that the morphology of the levator ani (LA) muscles influences the progress of the second stage of labour. Three-dimensional modelling of the LA muscle shape variations can help to identify structures that are potentially susceptible to labour-induced injuries. The first aim of this study was to use finite element modelling to study the geometrical variations of the normal PF muscles, using sets of magnetic resonance images from 12 normal nulliparous women. The effects of PF muscle shape variation on the mechanics of vaginal childbirth was then investigated using biomechanics simulations. During construction of the individual-specific PF models, point-to-point correspondence of anatomical features was achieved through a series of mathematical transformations. A principal component analysis (PCA) method was applied to the fitted PF models to compute the PF shape variations. The results were then used to construct the mean PF shape, plus four further PF models derived from the mean model and the first two primary modes of variation. These PCA-derived models were analysed using a biomechanical framework of the second stage of labour. The maximum principal stretch ratios and the forces required for delivery of a foetal head were quantified and analysed with respect to the geometry of each derived mode, to extract features of the PF muscles that are potentially susceptible to childbirth-induced injuries. The statistical shape analysis approach presented here may be extended to extract patterns of PF muscle morphological changes that are involved in PF dysfunction.


Pelvic Floor Mode Shape Pelvic Organ Prolapse Pelvic Floor Muscle Pubic Bone 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



X. Yan is financially supported by a University of Auckland Doctoral Scholarship. J. A. Kruger is supported by a Rutherford Foundation Postdoctoral Fellowship funded by the Royal Society of New Zealand. M. P. Nash and P. M. F. Nielsen are supported by James Cook Research Fellowships administered by the Royal Society of New Zealand on behalf of the New Zealand Government.


  1. 1.
    Carrière, B., Markel Feldt, C., Bø, K.: The Pelvic Floor, Thieme. xii, 476 p. ill. Stuttgart, New York, NY (2006)Google Scholar
  2. 2.
    Standring, S., Gray, H.A.: Gray’s anatomy: The Anatomical Basis of Clinical Practice. 40th edn. xxiv, p. 1551. Churchill Livingstone, Edinburgh (2008)Google Scholar
  3. 3.
    DeLancey, J., et al.: The appearance of levator ani muscle abnormalities in magnetic resonance images after vaginal delivery. Obstet. Gynecol. 101(1), 46 (2003)CrossRefGoogle Scholar
  4. 4.
    Fynes, M., O'Herlihy, C., O'Connell, P.R.: Childbirth and pelvic floor injury. In: Pemberton, J.H., Swash, M., Henry, M.M. (eds.) The Pelvic Floor: Its Function and Disorders, pp. 46–59. Saunders, Edinburgh (2002)Google Scholar
  5. 5.
    Dietz, H., Simpson, J.: Levator trauma is associated with pelvic organ prolapse. Br. J. Obstet. Gynaecol. 115(8), 979–984 (2008)CrossRefGoogle Scholar
  6. 6.
    Dietz, H.P., Gillespie, A.V.L., Phadke, P.: Avulsion of the pubovisceral muscle associated with large vaginal tear after normal vaginal delivery at term. Aust. N. Z. J. Obstet. Gynaecol. 47(4), 341–344 (2007)CrossRefGoogle Scholar
  7. 7.
    Kearney, R., et al.: Obstetric factors associated with levator ani muscle injury after vaginal birth. Obstet. Gynecol. 107(1), 144–149 (2006)CrossRefGoogle Scholar
  8. 8.
    Dietz, H.P.: Female pelvic organ prolapse and levator trauma. Ultrasound. Obst. Gyn. 30(4), 445–446 (2007)CrossRefGoogle Scholar
  9. 9.
    DeLancey, J.O.L.: The hidden epidemic of pelvic floor dysfunction: achievable goals for improved prevention and treatment. Am. J. Obstet. Gynecol. 192(5), 1488–1495 (2005)CrossRefGoogle Scholar
  10. 10.
    Dietz, H.P.: Levator function before and after childbirth. Aust. N. Z. J. Obstet. Gynaecol. 44(1), 19–23 (2004)CrossRefGoogle Scholar
  11. 11.
    Li, X.S., et al. Effects of fetal head motion on pelvic floor mechanics. Comput. Biomech. Med. Part 2, 129–137 (2010)Google Scholar
  12. 12.
    Dietz, H.P., Haylen, B.T., Broome, J.: Ultrasound in the quantification of female pelvic organ prolapse. Ultrasound. Obst. Gyn. 18(5), 511–514 (2001)CrossRefGoogle Scholar
  13. 13.
    Kruger, J.A., Dietz, H.P., Murphy, B.A.: Pelvic floor function in elite nulliparous athletes. Ultrasound. Obst. Gyn. 30(1), 81–85 (2007)CrossRefGoogle Scholar
  14. 14.
    Kruger, J.A., Murphy, B.A., Heap, S.W.: Alterations in levator ani morphology in elite nulliparous athletes: A pilot study. Aust. N. Z. J. Obstet. Gynaecol. 45(1), 42–47 (2005)CrossRefGoogle Scholar
  15. 15.
    Singh, K., Reid, W.M., Berger, L.A.: Magnetic resonance imaging of normal levator ani anatomy and function. Obstet. Gynecol. 99(3), 433–438 (2002)CrossRefGoogle Scholar
  16. 16.
    Lee, S.L., et al.: Statistical shape modelling of the levator ani with thickness variation. MICCAI 3216, 258–265 (2004)Google Scholar
  17. 17.
    Kruger, J.A., et al.: Comparison of pelvic floor function in nulliparous elite athletes and nulliparous controls. Neurourol. Urodyn. 25(6), 525–526 (2006)Google Scholar
  18. 18.
    Continuum mechanics, image analysis, signal processing and system identification. Accessed date 11.08.2011,
  19. 19.
    Wold, S., Esbensen, K., Geladi, P.: Principal component analysis. Chemom. Intell. Lab. Syst. 2(1–3), 37–52 (1987)CrossRefGoogle Scholar
  20. 20.
    Prautzsch, H., Boehm, W., Paluszny, M.: Bézier and B-spline Techniques. Mathematics and Visualization, xiv, p. 304. Springer, Berlin (2002)Google Scholar
  21. 21.
    Mahfouz, M., et al.: Automatic methods for characterization of sexual dimorphism of adult femora: distal femur. Comput. Method. Biomech. Biomed. Eng. 10(6), 447–456 (2007)CrossRefGoogle Scholar
  22. 22.
    Rosse, C., Gaddum-Rosse, P., Hollinshead, W.H. The pelvis. In: Hollinshead's Textbook of Anatomy, pp. 641–647, Lippincott-Raven Publishers, Philadelphia, PA (1997)Google Scholar
  23. 23.
    Lapeer, R.J., Prager, R.W.: Fetal head moulding: finite element analysis of a fetal skull subjected to uterine pressures during the first stage of labour. J. Biomech. 34(9), 1125–1133 (2001)CrossRefGoogle Scholar
  24. 24.
    Li, X.: Modelling levator ani mechanics during the second stage of labour. 2011, Bioengineering-University of Auckland. p. 190. xxiv (2011)Google Scholar
  25. 25.
    Jing, D.J., Ashton-Miller, J.A., DeLancey, J.O.L.: A biomechanical analysis of the effect of pelvic floor ripening on predicted second stage of labor duration. J. Womens Health 18(10), 1514–1515 (2009)Google Scholar
  26. 26.
    Li, X., et al.: Effects of nonlinear muscle elasticity on pelvic floor mechanics during vaginal childbirth. J. Biomech. Eng. 132(11), 111010 (2010)CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media, LLC 2012

Authors and Affiliations

  • Xiani Yan
    • 1
  • Jennifer A. Kruger
    • 1
  • Martyn P. Nash
    • 1
    • 2
  • Poul M. F. Nielsen
    • 1
    • 2
  1. 1.Auckland Bioengineering InstituteThe University of AucklandAucklandNew Zealand
  2. 2.Department of Engineering ScienceThe University of AucklandAucklandNew Zealand

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