Obstetric trauma, pelvic floor injury and fecal incontinence: a population-based case-control study

Abstract

Objectives: Current concepts based on referral center data suggest that pelvic floor injury from obstetric trauma is a major risk factor for fecal incontinence (FI) in women. In contrast, a majority of community women only develop FI decades after vaginal delivery, and obstetric events are not independent risk factors for FI. However, obstetric events are imperfect surrogates for anal and pelvic floor injury, which is often clinically occult. Hence, the objectives of this study were to evaluate the relationship between prior obstetric events, pelvic floor injury, and FI among community women.

Methods: In this nested case-control study of 68 women with FI (cases; mean age 57 years) and 68 age-matched controls from a population-based cohort in Olmsted County, MN, pelvic floor anatomy and motion during voluntary contraction and defecation were assessed by magnetic resonance imaging. Obstetric events and bowel habits were recorded.

Results: By multivariable analysis, internal sphincter injury (cases-28%, controls-6%; odds ratio (OR): 8.8; 95% confidence interval (CI): 2.3-34) and reduced perineal descent during defecation (cases-2.6 ± 0.2 cm, controls-3.1 ± 0.2 cm; OR: 1.7; 95% CI: 1.2-2.4) increased FI risk, but external sphincter injury (cases-25%, controls-4%; P<0.005) was not independently predictive. Puborectalis injury was associated (P<0.05) with impaired anorectal motion during squeeze, but was not independently associated with FI. Grades 3-4 episiotomy (OR: 3.9; 95% CI: 1.4-11) but not other obstetric events increased the risk for pelvic floor injury. Heavy smoking (≥ 20 pack-years) was associated (P=0.052) with external sphincter atrophy.

Conclusions: State-of-the-art imaging techniques reveal pelvic floor injury or abnormal anorectal motion in a minority of community women with FI. Internal sphincter injury and reduced perineal descent during defecation are independent risk factors for FI. In addition to grades 3-4 episiotomy, smoking may be a potentially preventable, risk factor for pelvic floor injury.

Figure 1

Axial endoanal MR images in a 76 year-old female without fecal incontinence (control). Axial images in the upper (A), mid (B), and lower anal canal (C) demonstrate slightly intense T2 signal in the internal sphincter (small white arrows), and low T2 signal, similar to skeletal muscle, in the external anal sphincter (larger white arrows) and puborectalis (A, white arrowheads).

Figure 2

Adjacent axial endoanal MR images in a 51 year-old female with fecal incontinence. Observe the anterior internal anal sphincter tear (small arrows) with a smaller defect and marked focal thinning in the adjacent external anal sphincter (black arrowheads).

Figure 3

Coronal (A) and axial (B) endoanal MR images in a 85 year-old female with fecal incontinence shows diffuse atrophy of the external anal sphincter (small black arrows) below the level of the puborectalis (large white arrows). External sphincter atrophy accentuates the fascicles of the internal anal longitudinal muscle (black arrowhead). The internal sphincter appears normal (small white arrows)

Figure 4

Axial endoanal MR images in a 64 year-old female with fecal incontinence demonstrates an old tear with atrophy of the right puborectalis (white arrowhead, A) with a normal-appearing left puborectalis (black arrowhead, A) in the upper anal canal. In the lower anal canal, there is an anterior tear of the internal anal sphincter (white arrows, B) with an intact internal anal sphincter posteriorly (white arrowheads, B).