In silico prediction of maximum perineal muscle strain during vaginal delivery by design of experiment

Abstract

Background and Objective: The prevalence of childbirth-induced pelvic floor muscle injuries is higher than 23% in the general women population. Such injuries lead to prolapses and other pathologies in future female life. With the advantage of computational biomechanics, the study implements an advanced female pelvic floor model for calculating the maximum pelvic muscle strain as an injury risk indicator. The Design of Experiment method (further referred to as DoE) is implemented to calculate the maximum strain for boundary values of bony pelvis dimensions (anterior-posterior Diameter further referred to as APD and transverse diameter (further referred to as TD) in combination with small, medium and large fetal head circumference (further referred as HC) percentile. Methods: We have implemented a previously developed finite element female pelvic floor model as a reference and updated it with new features (more detailed tissue geometry and advanced constitutive material models). APD and TD were identified from the set of MRI of 64 nulliparous women to expect the boundary female bony pelvis dimensions employing combinations of small and large APD and TD. Together with the 10th and the 95th percentiles for HC, a three-dimensional domain was established for assessing the maximum pelvic muscle strain. The maximum pelvic muscle strain was calculated at 8 full-factorial design models in boundary cases (each at one corner of the domain to combine minimum and maximum APD, TD and HC) to define a response surface for predicting the maximum pelvic muscle strain inside the domain. The response surface prediction was validated using 15 additional intermediate design models at points in the centre of the domain (1 point), centres of the domain boundary surfaces (6 points) and in the middle of each domain boundary edge (8 points). Results: The maximum strain results for 8 combinations of APD, TD and HC were used to design a linear response surface as a function of APD, TD and HC. Calculations at an additional 19 domain points served to prove the performance of the response surface prediction. The response surface shows good predictability with an absolute average error of 1.52%, an absolute median error of 1.52% and an absolute maximum error of 11.11%. The most influencing dimension is HC with 16% of influence.Conclusions: The reference finite element pelvic floor model was scaled to 8 full-factorial female-specific pelvic floor models representing the combination of boundary values for APD, TD and HC. The maximum pelvic floor muscle strain at those 8 corners was used to design a response surface. DoE implementing the response surface shows good predictability for the maximum perineal muscle strain by validating at the additional 19 intermediate design models. The response surface methodology can be used as one of the initial predictors for childbirth-induced pelvic floor muscle injury.