The Effect Of Helmet Loads On Cervical Spine Musculature, Intradiscal Pressure, And Facet Joint Forces

BACKGROUND: As many as 97% of fighter pilots report experiencing neck pain. This pain has been directly linked to their helmets and interferes with their flying, causes sick leave, and costs the military millions of dollars. The purpose of this study is to use finite element models (FEMs) to analyze the effects of the helmet loads on cervical spine tissues. A secondary purpose is to validate the muscle loads and intervertebral disc (IVD) properties in this FEM. METHODS: Two simulations were run with the previously validated VIVA OpenHBM head and neck model. The no helmet (NH) simulation was loaded with gravity and muscle forces. The helmet (H) was loaded the same with the addition of the helmet mass. A PID controller was used to estimate muscle activation required to stabilize the head in a neutral position. RESULTS: The NH reaction force at each IVD was 72.116.6 N. This corresponds well with previous literature estimating the head weight and muscle forces to be 73.6 N on each IVD. There were large increases in reaction forces from NH (72.1+/-16.6 N) to H (90.1+/-13.4 N). Total muscle forces increased from 149.0 N (NH) to 164.1 N (H). IVD pressure distributions correlate well with previous reports in the literature at CORA = 0.8778 (NH) and CORA = 0.8539 (H). IVD pressure magnitude increases from NH (0.50+/-0.07 MPa) to H (0.65+/-0.11 MPa). Facet joint forces decreased by 0.85+/-0.69 N from NH to H at all levels except C5C6 where forces increased by 4.1 N. CONCLUSIONS: The helmet load is 19 N and muscle forces increased 15 N, but IVD reaction forces only increased 18 N and the total facet force magnitude stayed the same. Thus, other structures in the spine must be taking on supraphysiological loads that may be causing pain and tissue damage. The reaction force magnitude and IVD pressures correlate well with previously reported data, validating the IVD material properties and PID method for muscle activation. This research was funded by the Office of Naval Research [N000142112649]. Supported by: This research was funded by the Office of Naval Research [N000142112649].