On the mechanical aspects of shoulder dystocia and birth injury.

This article presents objective evidence about shoulder dystocia and its associated mechanical injuries, namely clavicle fractures, and brachial plexus injuries. Specifically, the review focuses on the mechanical response of the fetus to forces applied to it or its anatomic components, including possible force thresholds for injury. This is followed by presenting the medical and engineering literature on the mechanical aspects of shoulder dystocia with emphasis on kinematics, the forces associated with labor and with traction forces associated with delivery. Finally, the paper discusses the mechanical characteristics of maternal and fetal maneuvers for shoulder dystocia and demonstrates how shoulder dystocia models can be used to train clinicians in the performance of maneuvers that stress the fetus the least. From a mechanical point of view, there are obstetric methods and training that can be employed to reduce the stresses induced by the fetus while alleviating shoulder dystocia, thereby reducing, but not eliminating, the risk of mechanical injury.