Neck segment loading in a dummy model: Effect of compression and lateral bending

Abstract

Previous research has shown that it is difficult effectively to reduce cervical compression under conditions of axial loading. In this study, the effect on the magnitude of cervical compression of diverting the line of action of the axial force, through lateral bending of the head at impact, was examined. Collision simulations were conducted with a Hybrid III anthropometric test dummy (ATD) propelled head first to strike a rigid barrier. The barrier had been placed to produce angles of incidence of 70° and 50° to the ATD's line of flight. Compressive and shear forces and moments of force were obtained from a three-axis force-and-moment transducer located at the atlanto-occipital junction of the ATD. A postprocessing model was developed to predict the loading on each segment of the ATD neck. Displacement data were obtained from an infrared imaging system using two cameras placed 60° apart, and infrared light-emitting diodes were fixed to the metal rings of the ATD neck. The collision simulations were also filmed at 500 frames per second to provide a top-coronal-plane view of the ATD under impact. Impact analysis showed large compressive forces (>4,000 N) and large shear forces (600-1,200 N) on the ATD segments for the 70° impacts. For the 50° impacts, however, the compression force (2,200 N) was markedly reduced as were the shear forces (300-450 N). Film observation confirmed that for the 70° impacts, the head was constrained on the impact surface, trapping the neck between the fixed head and moving torso. For the 50° condition, the head was free to move in a lateral direction, the neck was not trapped, and the compression force was substantially lowered. These results suggest that neck compression can be reduced in the ATD provided there is enough lateral bending. Whether shear forces and the moments of force produced by the lateral bending can be supported in real life by the cervical column (e.g., ligaments, disks, and muscles) requires further investigation.