Prolapse of the anterior and posterior vaginal walls has been generally associated with apical descent and levator ani muscle defects. However, the relative contributions of these factors to the pathophysiology of descent in the different vaginal compartments is not well understood. Furthermore, symptoms uniquely associated with prolapse in these compartments have not been well characterized.

The objectives of the study were to compare the associations between the following: (1) apical support, (2) levator ani muscles, and (3) pelvic floor symptoms in women with posterior-predominant prolapse, anterior-predominant prolapse, and normal support.

This is a cross-sectional study with 2 case arms: 60 women with posterior prolapse, 90 with anterior prolapse, and a referent control arm with 103 asymptomatic subjects with normal support, determined from pelvic organ prolapse quantification examinations. Levator muscle defects were graded from magnetic resonance imaging. Vaginal closure forces above resting were measured with an instrumented speculum during maximal contraction. Pelvic floor symptoms were measured via the Pelvic Floor Distress Inventory–Short Form.

Mean point C location in controls was –6.9 cm [1.5] (mean [standard deviation]); and was higher in posterior prolapse (–4.7 cm [2.7], 2.2 cm below controls) than the anterior prolapse group (–1.2 cm [4.1]; 5.6 cm below controls, P < .001 for all comparisons). Normal-appearing muscles (ie, muscle without a visible defect) occurred at similar frequencies in posterior prolapse (45%) and controls (51%, P = .43) but less often in anterior prolapse (28%, P ≤ .03 for pairwise comparisons). Major levator ani defects occurred at similar rates in women with posterior (33%) and anterior prolapse (42%, P = .27) but less often in controls (16%, P ≤ .012 for both pairwise comparisons). Similarly, there were significant differences in generated vaginal closure forces across the 3 groups, with the prolapse groups generating weaker closure forces than the control group (P = .004), but the differences between the 2 prolapse groups were not significant after controlling for prolapse size (P = .43). Pelvic floor symptoms were more severe for the posterior (mean Pelvic Floor Distress Inventory score, 129) and anterior prolapse groups (score, 128) than the controls (score, 40.2, P < .001 for both comparisons); the difference between the 2 prolapse groups was not significant (P = .83).

Posterior-predominant prolapse involves an almost 3-fold less apical descent below normal than anterior-predominant vaginal prolapse. Levator ani defects and muscle impairment also have a lower impact. Pelvic floor symptoms reflect the presence and size of prolapse more than the predominant lax vaginal compartment.