Effects of bilateral levator ani nerve injury on pelvic support in the female squirrel monkey

Abstract

Objective: To determine whether experimental denervation of the levator ani (LA) and its subsequent atrophy contribute to the development of pelvic organ prolapse in the squirrel monkey.

Study design: Thirty-seven female monkeys were evaluated including 7 that underwent bilateral LA neurectomy (bLAN), 17 nulliparous monkeys without prolapse, 7 parous monkeys without prolapse, and 6 parous monkeys with prolapse. Magnetic resonance imaging was used to calculate LA muscle volumes and obtain measurements of the position of bladder and cervix. Repeat observations in bLAN females occurred at different times in relation to parturition.

Results: LA volumes were reduced in bLAN monkeys (P = .02). Bladder (P = .03) and cervix (P = .04) positions varied between groups, with nulliparous females having the most cephalad positions and females with prolapse having the most caudal positions. Bladder descent was observed in a subset of 4 bLAN females that experienced vaginal parturition (P = .04) and correlated with external findings of vaginal prolapse.

Conclusion: Bilateral transection of the LA nerve results in atrophy of denervated LA muscles but not a loss of pelvic support in nulliparous monkeys, suggesting that connective tissue components compensate for weakened pelvic floor muscles. LA denervation may accelerate the onset of vaginal prolapse subsequent to parturition.