Introduction: Shoulder dystocia is where the infants anterior shoulder becomes stuck against the maternal symphysis pubis after the delivery of the fetal head. This condition requires intervention to avoid severe complications, including brachial plexus injuries. The objective of this study was to evaluate the effects of different maneuvers (McRoberts, Suprapubic Pressure ( SPP) of 100 N, Oblique and Posterior Arm) on the forces required for delivery and the resulting stretch on the brachial plexus using computer models of a maternal pelvis and a neonate.
Materials and
Methods: To model the various birthing maneuvers and investigate the brachial plexus (BP) stretch, we used MADYMO (Mathematical Dynamic Models, version 2312, The Netherlands) software. In MADYMO, a 90th percentile newborn infant and a 50th percentile maternal pelvis was modeled (Joy et al., 2024). The BP was modeled as a 7.5 cm long nonlinear spring. The following delivery maneuver were simulated in a shoulder dystocia condition and delivery force was identified while a 82 N maternal force was applied (at the center of gravity of the neonate): 1. McRoberts Maneuver: Maternal legs were flexed to the body. 2. SPP (100 N): Application of a downward directed 100 N force above the pubic bone. 3. Oblique Positioning: Rotation of the fetal shoulders by 15°. 4. Posterior Arm Delivery: Taking the posterior arm out prior to delivery simulation. The delivery force was defined as the minimum amount of force needed to deliver. BP stretch during delivery force was measured for each scenario, with the strain reported as the change in length divided by the original length, corresponding to the required delivery force in the simulation. Clinician-applied traction was modeled as a downward axial force at a 45-degree angle from the horizontal axis. In each case, the clinician-applied force was increased until the infant delivered. Successful delivery was defined baby's shoulder cleared the maternal pelvis. Results were summarized for the required delivery force and the resulting strain on the brachial plexus as the models were simulated through various maneuvers.
Results, Conclusions, and Discussions: The study used a MADYMO model featuring a 90th percentile newborn infant and a 50th percentile maternal pelvis (Figure 1). There was a maternal force of 82 N. Table 1 displays the BP stretch results for different maneuvers and forces simulated.
The maneuvers developed over the past decades aim to minimize injury to both the infant and mother by reducing the delivery force and BP stretch. The study's simulations demonstrated that each maneuver significantly reduces delivery force and BP stretch, which are important factors in preventing BP injuries. The McRoberts maneuver, while effective in reducing delivery force, it still resulted in a relatively high BP stretch, indicating a risk of BP injury. When doing SPP 9100 N), a moderate reduction in both delivery force and BP stretch was observed. Most effective in reducing BP stretch was the Posterior Arm Delivery but it is also already associated with risk of fractures and is the most invasive, making it less practiced despite its effectiveness. Oblique Positioning significantly reduced BP stretch. While useful, some limitations of the model include the inability to measure real-time forces and tissue strains in actual deliveries and the lack of data for accurate injury risk prediction. However, the trends observed in the model simulations provide valuable insights for clinical practices and is a promising educational tool for clinician training in injury prevention of BP.
Conclusion: The studies simulations highlight that common obstetrical maneuvers effectively reduce delivery force and brachial plexus stretch which are key factors in minimizing the risk of BP injury during shoulder dystocia. Posterior arm delivery, while most effective in reducing BP
stretch, carries higher risks, may be challenging to perform and is more invasive. Suprapubic pressure and oblique positioning offer a good balance between reducing delivery force and BP stretch. These findings show the importance of training clinicians in a range of maneuvers to ensure they can respond effectively based on the specific circumstances of complicated delivery. Future studies should focus on refining these models with more comprehensive biomechanical data and exploring the long-term outcomes associated with each maneuver.
Acknowledgements (Optional): I would like to thank my mentor Dr. Anita Singh for all her valuable support in helping me understand the computational approaches to solve a real world clinical problem.
