Assessing the Tissue-Level Response and the Risk of Neck Pain in Rotary-Wing Aircrew using a Finite Element Model of the Neck

Abstract

Epidemiological studies report a prevalence of neck pain among rotary-wing aircrew (RWA) potentially associated with head-supported mass (HSM), frequent physiologic motions of head-neck, aircraft vibration, and prolonged time in non-neutral head-neck positions. Experimental studies with human volunteers and computational studies using head-neck models have suggested potential causal pathways for neck pain in RWA, including increased activity in muscles and increased forces in the spinal column. However, additional insight is required to understand the interactions of HSM, which comprises a helmet with optional mounted devices, and non-neutral head-neck positions. The present study aimed to simulate RWA non-neutral head-neck positions with the HSM using a detailed finite element (FE) head-neck model to assess the tissue-level biomechanical response and potential sources for neck pain in RWA. A detailed FE head-neck model (NMM50) was extracted from a full human body model of a 50th percentile male. The NMM50 model was enhanced, verified and validated starting sequentially from the ligamentous upper cervical spine (UCS), full cervical spine, and full head-neck with active musculature for physiologic loading conditions (NMM50-Hill-E). The NMM50-Hill-E model was simulated for non-neutral head-neck positions (flexion and axial rotation) using a conventional boundary condition and a novel active muscle repositioning approach, demonstrating the importance of active muscle repositioning on tissue-level response. Finally, the NMM50-Hill-E model with active muscle repositioning was simulated for non-neutral head and neck positions with HSM. The present study demonstrated that the muscle-based method of repositioning the FE head-neck model improved the head and neck kinematic response by capturing the in vivo flexion and axial rotation positions better than the conventional boundary condition method. In the simulated RWA head-neck positions, tissue-level investigations demonstrated an increase in the muscle force, intervertebral disc (IVD) force, endplate stress and annulus fibrosus(AF) collagen fiber strain with an increase in the HSM in flexion. Similarly, an increase in the magnitude of non-neutral position from flexion to a combined position was shown to increase the ligament distraction along with an increase in muscle force, IVD force, endplate stress and AF collagen fiber strain. The detailed FE head-neck model provided valuable insight by predicting tissue-level biomechanical responses in the RWA neck while providing guidance on factors that may contribute to neck pain risk in the RWA.