Association Between Uterine Version, Uterine Position, and Vaginal Wall Length Among Patients With Posterior Predominant Prolapse

INTRODUCTION: Pelvic organ prolapse (POP) is thought to be more common with uterine retroversion. The anterior vaginal walls of patients with retroverted uteri have been found to be shorter than patients with anteverted uteri. No studies have described the association between uterine version and flexion, vaginal wall length, and the leading compartment of POP. OBJECTIVE: To compare the frequency and degree of uterine version, uterine flexion, and anterior and posterior vaginal wall lengths in subjects with posterior compartment POP to controls without POP. We hypothesized that posterior POP would be associated with higher rates and greater degrees of uterine retroversion and retroflexion. We also hypothesized that posterior POP subjects would have shorter anterior and longer posterior vaginal walls. METHODS: We performed a retrospective cohort study using a preexisting MRI biorepository. We identified 38 subjects with posterior compartment POP as the leading edge of their prolapse on POP-Q and 38 controls without POP. On resting mid-sagittal images, 3D Slicer was used to measure the cervico-vaginal angles (angle created by the cervical and vaginal axes utilizing previously defined points at the internal cervical os, external cervical os, and vaginal introitus) (Figure 1A) and cervico-uterine angles (angle created by the cervical and uterine axes utilizing points at the external os, internal os, and uterine fundus) (Figure 1B). Anteversion was defined as a cervico-vaginal angle <180° and retroversion as ≥180°. Anteflexion was defined as a cervico-uterine angle <180° and retroflexion as ≥180°. Anterior vaginal walls were measured as a curved line between the external urethral meatus and anterior vaginal fornix (Figure 2A). Posterior vaginal walls were measured as a curved line between the mid-perineal body and posterior vaginal fornix (Figure 2B). Uterine version and flexion rates were compared between posterior POP and control subjects with chi-square statistics. Average cervico-vaginal angles, cervico-uterine angles, and vaginal wall lengths between groups were compared with t-tests. Significance set at p<0.05. RESULTS: A cohort of 38 posterior POP subjects and 38 controls without POP was analyzed. Mean age (55.9 ± 10.6 vs 54.8 ± 11.5 years) and BMI (28 ± 5.4 vs 27 ± 5.8 kg/m2) between posterior POP subjects and controls, respectively, did not vary (all p>0.05). Average Bp on patients with posterior POP was +2.0 ± 1.5 cm. Uterine retroversion and retroflexion rates among POP subjects did not differ from controls (13% (5/38) vs 8% (3/38), p=0.45 and 40% (15/38) vs 32% (12/38), p=0.47, respectively). Posterior POP subjects had larger average cervico-vaginal angles than controls (140.8° ± 33.4° vs 116.4° ± 32.7°, p=0.002), but there was no difference in average cervico-uterine angles (177.7° ± 42.4° vs 176.5° ± 28.6°, p=0.89). Posterior POP subjects had shorter anterior vaginal walls than controls (52.5 ± 14.7 mm vs 61.4 ± 10.1 mm, p=0.003), but posterior vaginal wall lengths did not vary (87.4 ± 23 mm vs 90.6 ± 15.9 mm, p=0.49). CONCLUSIONS: Posterior POP subjects had larger average cervico-vaginal angles and shorter anterior vaginal walls than controls. Rates of uterine retroversion and retroflexion, average cervico-uterine angles, and posterior vaginal wall lengths were similar between groups.