Predicting neck injuries due to head-supported mass.

BACKGROUND: Technological advances in military equipment have resulted in more devices being mounted on the helmet to enhance the capability of the soldier. The soldier's neck must bear this head-supported mass (HSM) and the resulting dynamic characteristics of the head and neck system are changed. The purpose of this study was to vary the conditions of impact as well as the design criteria to quantify the effect of HSM on neck injury risk through computational modeling. METHODS: The TNO MADYMO detailed neck model was used for a matrix of 196 simulations designed to vary the impact conditions and HSM properties added to the model. These parameters included seven impact directions, three impact magnitudes, nine mass locations, and three mass magnitudes. The data collected from these simulations were evaluated for injury risk using the lower neck beam criterion equation. RESULTS: The results from these simulations provide detailed information regarding the risk of injury based on a particular HSM configuration and the acceleration of the body. The predominant factor in increasing risk in the lower neck is the increase in pulse magnitude. The effect of pulse magnitude is more dominant in the directions that create a flexion or lateral bending moment. CONCLUSION: HSM increases the level of injury, but the impact level that the subject is exposed to is a more dominating factor in determining injury risk.

Upper extremity interaction with a helicopter side airbag: injury criteria for dynamic hyperextension of the female elbow joint.

This paper describes a three part analysis to characterize the interaction between the female upper extremity and a helicopter cockpit side airbag system and to develop dynamic hyperextension injury criteria for the female elbow joint. Part I involved a series of 10 experiments with an original Army Black Hawk helicopter side airbag. A 5(th) percentile female Hybrid III instrumented upper extremity was used to demonstrate side airbag upper extremity loading. Two out of the 10 tests resulted in high elbow bending moments of 128 Nm and 144 Nm. Part II included dynamic hyperextension tests on 24 female cadaver elbow joints. The energy source was a drop tower utilizing a three-point bending configuration to apply elbow bending moments matching the previously conducted side airbag tests. Post-test necropsy showed that 16 of the 24 elbow joint tests resulted in injuries. Injury severity ranged from minor cartilage damage to more moderate joint dislocations and severe transverse fractures of the distal humerus. Peak elbow bending moments ranged from 42.4 Nm to 146.3 Nm. Peak bending moment proved to be a significant indicator of any elbow injury (p = 0.02) as well as elbow joint dislocation (p = 0.01). Logistic regression analyses were used to develop single and multiple variate injury risk functions. Using peak moment data for the entire test population, a 50% risk of obtaining any elbow injury was found at 56 Nm while a 50% risk of sustaining an elbow joint dislocation was found at 93 Nm for the female population. These results indicate that the peak elbow bending moments achieved in Part I are associated with a greater than 90% risk for elbow injury. Subsequently, the airbag was re-designed in an effort to mitigate this as well as the other upper extremity injury risks. Part III assessed the redesigned side airbag module to ensure injury risks had been reduced prior to implementing the new system. To facilitate this, 12 redesigned side airbag deployments were conducted using the same procedures as Part I. Results indicate that the re-designed side airbag has effectively mitigated elbow injury risks induced by the original side airbag design. It is anticipated that this study will provide researchers with additional injury criteria for assessing upper extremity injury risk caused by both military and automotive side airbag deployments.