UroToday – It is generally accepted that vaginal childbirth is an important factor in the pathogenesis of female pelvic organ prolapse. Large epidemiological studies leave little doubt that childbirth can impair pelvic organ support (1). This study was designed to quantify the role of a recently identified aetiological factor, i.e, direct trauma, to the insertion of the puborectalis muscle on the inferior pubic ramus. Such trauma is common (2, 3) and clearly linked to vaginal delivery (4, 5).
In our population the presence of an identified levator defect approximately doubled the risk of significant prolapse (RR 1.9, CI: 1.7-2.1). The prevalence of levator avulsion was about four times greater in women with significant clinically diagnosed pelvic organ prolapse (POP-Q Stage 2 or higher) than in women without prolapse. The association was strongest for the anterior and central compartments, and patients with bilateral avulsion were particularly likely to suffer from uterine prolapse (relative risk of 7.1).
Our findings are consistent with results recently obtained by magnetic resonance imaging where patients with prolapse were more likely to have major levator ani defects than controls (55% compared with 16%), with an adjusted odds ratio of 7.3 (95% confidence interval 3.9-13.6) (6). When we analysed our data to allow for comparison of data, we obtained an unadjusted odds ratio of 6.1 (CI 4.0-9.3), with 150/415 (36%) of prolapse patients showing an avulsion compared to 31/366 (8%) without significant prolapse.
The association between prolapse and levator trauma is not surprising given that avulsion injury has a marked effect on hiatal dimensions, distensibility and contractility, and effect that has been shown by palpation (7), instrumented speculum (6) and ultrasound imaging (8). Together, these data further strengthen the aetiological link between childbirth and female pelvic organ prolapse. It now seems very likely that delivery-related major levator trauma is a significant factor in the pathogenesis of prolapse. This is particularly obvious for cystocele and uterine prolapse.
Undoubtedly however, levator avulsion is not the only mechanism by which pelvic floor muscle function and pelvic organ support may be impaired. Childbirth clearly leads to an enlargement of the levator hiatus, even if avulsion injury does not ensue (9), and such over-distension of an intact muscle may equally predispose to prolapse. Finally, it is very likely that congenital factors and/ or fascial trauma play a role in many women, even if both may be much more difficult to identify than muscular trauma.
The identification of a major modifiable risk factor opens up novel opportunities for prevention. Levator avulsion is likely to be a useful intermediate outcome variable for intervention studies. Any change in clinical practice resulting in a reduced prevalence of levator avulsion would be expected to have a positive effect on the prevalence of significant prolapse later in life. We are currently undertaking two randomized controlled trials aimed at reducing the incidence of levator avulsion in childbirth, using antenatal intervention strategies.
One of the more obvious weaknesses of our study is the fact that it was undertaken in a urogynaecological population. While the majority of our patients did not complain of symptoms of prolapse, they were certainly not asymptomatic as they presented with other urogynaecological complaints. It remains to be shown to what extent these results are applicable to the general population. Furthermore, operators were not blinded against prolapse findings when they assessed for levator defects. We do not expect this bias to be significant: in an unrelated study examining the repeatability of the digital detection of levator trauma, the association between prolapse and defects was in fact stronger for the examiner who was blinded against clinical data than in the operator who undertook the levator assessment immediately after examining for prolapse (unpublished own data). However, we can not exclude that bias may have contributed to the association observed in this population.
It would be preferable to confirm findings by using a study design that separates prolapse assessment and the diagnosis of levator injury, allowing for blinding of operators. In addition, longitudinal cohort studies need to be undertaken in order to monitor the medium- term effect of levator trauma on pelvic organ support after childbirth, and to ascertain the role of avulsion injury in recurrence after reconstructive surgery.
1. DeLancey J. The hidden epidemic of pelvic floor dysfunction: achievable goals for improved prevention and treatment. Am J Obstet Gynecol 2005;192:1488- 95.
2. Kearney R, Miller J, Ashton-Miller J, Delancey J. Obstetric factors associated with levator ani muscle injury after vaginal birth. Obstet Gynecol 2006;107(1):144-9.
3. Dietz HP, Steensma AB. The prevalence of major abnormalities of the levator ani in urogynaecological patients. BJOG: An International Journal of Obstetrics & Gynaecology 2006;113(2):225-30.
4. Dietz H, Gillespie A, Phadke P. Avulsion of the pubovisceral muscle associated with large vaginal tear after normal vaginal delivery at term. Aust NZ J Obstet Gynaecol 2007;47:341-4.
5. Lien KC, Mooney B, DeLancey JO, Ashton-Miller JA. Levator ani muscle stretch induced by simulated vaginal birth. Obstet Gynecol 2004;103(1):31-40.
6. DeLancey J, Morgan D, Fenner D, et al. Comparison of levator ani muscle defects and function in women with and without pelvic organ prolapse. Obstetrics & Gynecology 2007;109(2):295-302.
7. Dietz HP, Shek C. Levator Avulsion and Grading of Pelvic Floor Muscle Strength. Int Urogynecol J 2008;in print.
8. Abdool Z, Shek K, Dietz H. The effect of levator avulsion on hiatal dimensions and function. Neurourol Urodyn 2008;27:in print.
9. Dietz H, Lanzarone V. Levator trauma after vaginal delivery. Obstet Gynecol 2005;106:707-12.
HP Dietz PhD, and JM Simpson PhD, as part of Beyond the Abstract on UroToday. This initiative offers a method of publishing for the professional urology community. Authors are given an opportunity to expand on the circumstances, limitations, etc., of their research by referencing the published abstract.
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