Abstract
A significant portion of the military population develops severe neck pain in the course of their duties. It has been hypothesized that neck pain is a consequence of accelerated degeneration of the intervertebral discs in the cervical spine, but more occupational and mechanistic-based tools and research are needed to positively confirm the link between neck pain and accelerated disc degeneration. Heavy head-supported mass including helmets and accessories worn by military personnel may subject the intervertebral discs of the cervical spine to complex cyclic loading profiles. In addition, some military operational travel which includes riding on high speed planing boats has also been reported to result in high magnitude cyclic loading on cervical spine discs. In this article, we present a methodology to computationally predict fatigue damage to cervical intervertebral discs over extended periods of time, by integrating kinematics-based biomechanical models with a continuum damage mechanics-based theory of disc degeneration. Through this computational approach, we can gain insights into the relationship between these military activities and possible accelerated fatigue degeneration of cervical intervertebral discs and provide a quantitative prediction tool for decade-long time ranges. The four significant improvements this computational framework adds to the area of modeling intervertebral disc degeneration are the following: (a) it addresses the non-linear nature of fatigue damage evolution, (b) it includes the effect of aging and damage recovery to accurately simulate biological phenomena, (c) it computes fatigue damage taking into account the multiaxial stress state in the disc, and (d) it correlates the computational damage parameter with established clinical grading systems for disc degeneration.
Highlights
The development of severe neck pain among personnel of the military is becoming a cause for concern.[1,2,3] Van den Oord and Veerle De Loose[1] conducted a study on military helicopter pilots and concluded that heavy helmets and associated head-mounted displays commonly used by these pilots may play a significant role in the development of neck pain
This article presents a structured framework for the prediction of fatigue damage in the cervical intervertebral disc annulus, due to long-term cyclic loading experienced by military personnel during combat operations such as walking with heavy head-supported equipment and riding a fast boat
The damage model proposed in this article considers damage evolution based on different causes of damage to the disc, and this is a novel contribution to the field of intervertebral disc degeneration
Summary
The development of severe neck pain among personnel of the military is becoming a cause for concern.[1,2,3] Van den Oord and Veerle De Loose[1] conducted a study on military helicopter pilots and concluded that heavy helmets and associated head-mounted displays commonly used by these pilots may play a significant role in the development of neck pain. In the damage model presented in this article, the signed Von-Mises stress measure shown in equation (13) was computed at every instant of the cyclic loading histories This equivalent stress measure was used to compute sa, smean, and smax for each load iteration, in order to estimate the multiaxial fatigue damage evolution in the disc annulus. Having determined all the parameters required by the damage model, we can apply the model to predict damage evolution in intervertebral discs over long periods of time due to walking with head-supported mass and due to riding a fast boat This model application process has been discussed in the ‘‘Results and discussion’’ section
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