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Pelvic floor muscle injury during a difficult labor. Can tissue fatigue damage play a role?

Abstract

Pubovisceral muscle (PVM) injury during a difficult vaginal delivery leads to pelvic organ prolapse later in life. If one could address how and why the muscle injury originates, one might be able to better prevent these injuries in the future. In a recent review we concluded that many atraumatic injuries of the muscle-tendon unit are consistent with it being weakened by an accumulation of passive tissue damage during repetitive loading. While the PVM can tear due to a single overstretch at the end of the second stage of labor we hypothesize that it can also be weakened by an accumulation of microdamage and then tear after a series of submaximal loading cycles. We conclude that there is strong indirect evidence that low cycle fatigue of PVM passive tissue is a possible mechanism of its proximal failure. This has implications for finding new ways to better prevent PVM injury in the future.

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Notes

  1. Note: The term tissue ‘fatigue’ in this context has nothing to do with muscle fatigue, which is a completely different physiological process adversely affecting the ability of muscle to generate contractile force.

  2. For the purpose of this paper, as we shall see, the ‘low’ in low-cycle fatigue refers to between 2 to 120 loading cycles.

  3. As opposed to the high-cycle fatigue failure found in many engineering materials after millions of loading cycles.

  4. Examples of this effect can be seen, for instance, when placing a human hair under too much tension. It then has a tendency to fail at the root, not in mid-shaft. Another example are the suture points from surgical repairs. Different techniques have been developed to reduce the stress concentration between the tissue and the stitches in order to reduce the risk of skin tearing.

  5. Defined as a change in length over the original length

  6. Maximum stress or strain that the material can withstand without failing.

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Acknowledgements

The authors gratefully acknowledge the support from Fundação para a Ciência e Tecnologia (Portugal) under grant SFRH/BD/136213/2018, the funding provided by LAETA (Portugal), under project UIDB/50022/2020, and the US Public Health Service grants 5P30AG024824-15, RC2 DK122379-01 and 5R01AR054821-09.

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Authors and Affiliations

Authors

Contributions

M.C.P. Vila Pouca: conceived the presented idea, manuscript writing; M.P.L. Parente: supervised the work, manuscript editing; R.M. Natal Jorge: supervised the work, manuscript editing; J.O.L. DeLancey: conceived the presented idea, supervised the work, manuscript editing; J.A. Ashton-Miller: conceived the presented idea, supervised the work, manuscript writing.

Corresponding author

Correspondence to Maria C. P. Vila Pouca.

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Conflicts of interests

M.C.P.V.P., M.P.L.P. and R.M.N.J. declare no conflicts of interest. J.O.L.D. and J.A.A-M.’s institution received US National Institutes of Health Grant R44 HD 096987 for them to analyze the Materna LLC Prep device data on the relationship between birth canal dilation force and displacement during the first stage of labor.

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Vila Pouca, M.C.P., Parente, M.P.L., Natal Jorge, R.M. et al. Pelvic floor muscle injury during a difficult labor. Can tissue fatigue damage play a role?. Int Urogynecol J 33, 211–220 (2022). https://doi.org/10.1007/s00192-021-05012-5

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  • DOI: https://doi.org/10.1007/s00192-021-05012-5

Keywords

  • Difficult vaginal delivery
  • Repetitive pushing
  • Material fatigue
  • Pelvic muscle injury