Although the catapult phase of pilot ejections has been well-characterized in terms of human response to compressive forces, the effect of the forces on the human body during the ensuing ejection phases (including windblast and parachute opening shock) have not been thoroughly reviewed. Both windblast and parachute opening shock have been shown to induce dynamic tensile forces in the human cervical spine. However, the human tolerance to such loading is not well known.
Therefore, the main objective of this research project was to help establish neck injury criteria for dynamic tensile loading, which could be used to develop safer equipment for individuals facing dynamic loading environments. Twelve human cadaver specimens, including 4 females and 8 males with a mean age of 50.1 ± 9 years, were tested dynamically until failure occurred. Failure load, failure strain, tensile stiffness, injury location, and injury type were documented.
In addition, various cofactors were measured and evaluated including body anthropometry, bone mineral density, and lifestyle factors. The mean failure load for the twelve specimens was 3100 ± 645 N, mean failure strain was 16.7 ± 5.4 %, and mean tensile stiffness was 172 ± 54.5 N/mm. Neck injury risk curves were developed based on tensile failure force and failure strain using survival analysis. The survival models predicted 5% risk of tensile neck injury at 2050 N and 8.1% strain and 22% risk at 2430 N and 11.1% strain. Tensile strain measurements indicate that spinal cord injury may happen prior to structural failure. The majority of injuries (8) occurred in the upper cervical spine (Oc- C3), and none took place in the mid-cervical region (C3-C5). Factors such as neck cross- sectional area and bone mineral density were not predictive of neck strength. However, smoking and osteophytic growth appear to be detrimental to tensile neck strength.
The results of this study assist in filling the existing void in dynamic tensile injury data and will aid in developing improved neck injury prevention designs and strategies.