Tissue-Level Neck Response in Rotary-Wing Aircrew With Head-Supported Mass Assessed With Finite Element Model

Epidemiological studies have reported a prevalence of neck pain among rotary-wing aircrew (RWA), attributed in part to head-supported mass (HSM) including helmet and night vision goggles (NVG). Combined HSM and movement of the head away from the neutral position results in increased muscle activation and increased loads in the neck; however, the effect of HSM has not been quantified at the tissue level. In the present study, the tissue-level response to HSM was investigated using a detailed human finite element head-neck (HN) model. Non-neutral HN positions were achieved by activating the neck muscles, and three conditions were simulated for 25° flexion: (1) baseline HN model (HN_F), (2) HN with helmet (HN_F-H), and (3) HN with helmet, NVG and counterweight (HN_F-N). In addition, a combined HN position was investigated with the helmet, NVG and counterweight, comprising 25° flexion, 8° lateral bending, and 23° axial rotation (HN_C-N). Endplate stresses and annulus fibrosus (AF) fiber strains increased by 17% and 4%, respectively, with the added helmet (HN_F to HN_F-H). Endplate stresses and AF fiber strains increased by 24% and 12%, respectively, with the inclusion of NVG and counterweight to the helmet (HN_F-H to HN_F-N). In HN_C-N, endplate stresses and AF fiber strains further increased by 10% and 9%, respectively, relative to HN_F-N. The addition of NVG and counterweight to the helmet had a stronger influence than the helmet alone. The results can potentially quantify the high incidence of neck pain in RWA and can be applied to assess the consequences of mass additions and distribution in future systems.