Pelvic Floor Biomechanics and Birth Injury

University Of Michigan At Ann Arbor, Ann Arbor MI

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Abstract

NIDDK's Bladder Progress Review Group and NICHD workshop on Female Pelvic Floor Disorders have identified the lack of an understanding of the biomechanics of the female pelvic floor as a critical knowledge gap impeding research. The aims of this research are therefore to use human anatomical material to: (1) Characterize the mechanical properties and architecture of the passive and active structural elements comprising the female pelvic floor, the vesical neck support system, and the urethra; (2) Test the null hypotheses that neither age nor parity affects the number of (a) striated muscle cells, (b) smooth muscle cells, (c) number of nerves or the elastic moduli of passive tissue elements; (3) Develop a 3-D biomechanical pelvic floor model with representations of fetal head geometry, muscles and nerves based on anatomic material and probabilistic atlas data from 30 young, 30 middle-age, 30 elderly continent women MR data; (4) Develop a three-muscle-layer 3-D biomechanical model of the urethra and compare predicted values to urethral closure pressure behavior measured in 90 Project 1 nullipara, as well as Project 2 and 3 patients; (5) Use 2- and 3-D lumped parameter and finite element models to simulate different aspects of vaginal birth and test hypotheses that (a) largest muscle strain occurs in the nulliparous' puboperineus muscle, and (b) largest nerve strain occurs in the nulliparous' inferior hemorrhoidal nerve; analyze effects of normal vs. abnormal fetal head size and orientation (e.g. occipito-posterior), rapid-descent (forceps) vs. slow second stage (epidural) as well as geometry, timing and extent of episiotomy. These observations will yield insight into pelvic floor biomechanics that can help direct future research into these long-neglected but important issues.