Mathematical Dynamic Modeling (MADYMO) of the Maternal Pelvis and Neonate for Simulating Shoulder Dystocia and Delivery

Introduction: During childbirth, the anterior fetal shoulder can get caught behind the maternal pelvis, resulting in shoulder dystocia [1,2]. This complication is reported in approximately 3% of vaginal births in the United States [3,4]. The most common injury associated with SD is brachial plexus (BP) injury [5-7]. The BP is a network of nerves located bilaterally from the C5 to T1 vertebrae and provides innervation to the arms [8]. During delivery, maternal forces contribute to the pushing of the neonate out of the birth canal. However, during shoulder dystocia the constant push forces increase the angle between the shoulder and the axis of the neck, leading to BP stretch injury or Neonatal Brachial Plexus Palsy (NBPP). NBPP is usually temporary but can be permanent in rare instances. Computational modeling can be used to investigate the effects of birthing maneuvers and delivery forces on BP stretch, as studying BP injury in a clinical setting has ethical limitations. Results from such modeling can help provide the data needed to provide clinicians with clinical training tools in the future.

Materials and

Methods: To model the various birthing maneuvers and investigate the BP stretch, MADYMO (Mathematical Dynamic Models, version 2312, The Netherlands) was utilized. The model consists of rigid body ellipsoids which represent the neonate and maternal pelvis [9-12]. In MADYMO, a 90th percentile newborn infant and a 50th percentile maternal pelvis was modeled. The BP is modeled as a 7.5 cm long nonlinear spring [7,13-15]. The delivery force is the minimum amount of force needed to deliver the neonate [16]. A force was considered the delivery force once the fetus’s shoulder cleared the maternal pelvis. The BP stretch was measured for each scenario and the strain was reported, which is change in length divided by the original length corresponding to the required delivery force in the simulation.

Results, Conclusions, and Discussions: The 90th percentile newborn infant and 50th percentile maternal pelvis MADYMO model utilized in this study is shown in Fig 1. The results of BP stretch at various maneuvers and forces can be seen in Table 1.

In the lithotomy position, highest required delivery force and BP stretch was reported. The McRoberts maneuver reported a slight reduction in the delivery force and the BP stretch when compared to lithotomy position. The next clinically recommended SPP maneuver was conducted in the McRoberts maternal position and reported no change when the SPP force was 40 N. However, higher SPP forces of both 100 N and 140 N resulted in a much lower force required for delivery and reduced the BP stretch. The reported decrease in the BP stretch due to higher SPP forces of 100 N and 140 N could be attributed to the compression of the neonatal shoulders that effectively remove the obstruction with the symphysis pubis as suggested in the literature [17].

The simulated results suggest that the clinical maneuvers utilized during shoulder dystocia conditions do help achieve delivery. Maternal positioning from lithotomy to McRoberts helps reduce BP strain and is further reduced with the application of SPP. The MADYMO models utilized in this study can serve as a promising clinical tool for understanding the mechanical effects of various maneuvers on BP stretch and associated injury risk.

Acknowledgements (Optional): This research was supported by funding from the Eunice Kennedy Shriver National Institute of Child Health and Human Development of the National Institutes of Health under Award Number R15HD093024 and R01HD104910A and NSF CAREER Award Number 1752513.

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