Neck forces in combat jet pilots-Application of opensim to calculate dynamic cervical spine loads in flight

INTRODUCTION: Prevalence of flight-related neck pain in fast jet aircrew is reportedly as high as 95%, sometimes affecting fitness to fly and longevity of active service. Whilst many studies have investigated neck kinematics and EMG of cervical musculature in different helmeted postures, there is a need to determine head on neck accelerations during flight to truly determine pilot peak and cumulative workloads. Quantifying cervical workloads in flight will inform risk predictions and pre-conditioning efforts in a way that EMG studies alone cannot.
METHODS: Three-dimensional motion data was collected using the VICON camera system from RAAF fast jet pilots performing common aerial combat head checks. Pilots were seated in an F/A-18A ejection seat. Dynamic graphical models were derived using Opensim software. Further models were developed to account for varying Gz profiles and 2 helmet types (HGU-55/P and JHMCS).
RESULTS: Peak ROM of cervical spine was found to be 27 degrees cervical rotation, 48 degrees extension and 33 degrees lateral flexion. Moments were highest at C7 vertebral segment, and both peak and cumulative sum of moments were highest in the extension hold position. The JHMCS helmet was associated with up to 20% more load at C7 than the HGU-55/P helmet. Every unit increase of Gz added approximately 10% to calculated loads at C7, and demonstrated a linear relationship with average moments at each cervical segment.
DISCUSSION: The Opensim model can be used to estimate neck forces associated with aerial combat head check movements. Quantifying neck forces dynamically is an important step towards workload monitoring for combat pilots. Further research is needed to examine relationships between workload and neck injury patterns.