Prediction of brachial plexus stretching during shoulder dystocia using a computer simulation model

Area of Science:

• Obstetrics and Gynecology
• Biomechanics
• Fetal Medicine

Background:

• Shoulder dystocia is a critical obstetric emergency.
• Brachial plexus injuries can occur during shoulder dystocia delivery.
• Understanding the biomechanics of brachial plexus stretching is crucial for injury prevention.

Purpose of the Study:

• To investigate the influence of maternal endogenous and clinician-applied forces on brachial plexus stretching during shoulder dystocia.
• To quantify brachial plexus deformation under different delivery scenarios.

Main Methods:

• A computer simulation model (MADYMO) was adapted with fetal and maternal pelvic anatomy.
• The brachial plexus was modeled as a spring with defined mechanical properties.
• Varying levels of endogenous and exogenous forces were applied to simulate delivery, measuring nerve stretch.

Main Results:

• Lithotomy positioning showed brachial plexus stretching of 15.7% (endogenous) and 14.0% (exogenous).
• The McRoberts maneuver reduced brachial plexus stretch by 53% (to 6.6%).
• Downward lateral fetal head displacement increased stretch by 30% compared to axial positioning.

Conclusions:

• Brachial plexus stretch is influenced by delivery force magnitude, force origin, pelvic orientation, and fetal head position.
• Both maternal and clinician forces contribute to brachial plexus deformation during shoulder dystocia.
• The McRoberts maneuver and appropriate fetal head management can mitigate brachial plexus stretching.