Quantitative cervical spine injury responses in whiplash loading with a numerical method of natural neural reflex consideration.

BACKGROUND AND OBJECTIVE: Neural reflex is hypothesized as a regulating step in spine stabilizing system. However, neural reflex control is still in its infancy to consider in the previous finite element analysis of head-neck system for various applications. The purpose of this study is to investigate the influences of neural reflex control on neck biomechanical responses, then provide a new way to achieve an accurate biomechanical analysis for head-neck system with a finite element model. METHODS: A new FE head-neck model with detailed active muscles and spinal cord modeling was established and globally validated at multi-levels. Then, it was coupled with our previously developed neuromuscular head-neck model to analyze the effects of vestibular and proprioceptive reflexes on biomechanical responses of head-neck system in a typical spinal injury loading condition (whiplash). The obtained effects were further analyzed by comparing a review of epidemiologic data on cervical spine injury situations. RESULT: The results showed that the active model (AM) with neural reflex control obviously presented both rational head-neck kinematics and tissue injury risk referring to the previous experimental and epidemiologic studies, when compared with the passive model (PM) without it. Tissue load concentration locations as well as stress/strain levels were both changed due to the muscle activation forces caused by neural reflex control during the whole loading process. For the bony structures, the AM showed a peak stress level accounting for only about 25% of the PM. For the discs, the stress concentrated location was transferred from C2-C6 in the PM to C4-C6 in the AM. For the spinal cord, the strain concentrated locations were transferred from C1 segment to around C4 segment when the effects of neural reflex control were implemented, while the gray matter and white matter peak strains were reduced to 1/3 and 1/2 of the PM, respectively. All these were well correlated with epidemiological studies on clinical cervical spine injuries. CONCLUSION: In summary, the present work demonstrated necessity of considering neural reflex in FE analysis of a head-neck system as well as our model biofidelity. Overall results also verified the previous hypothesis and further quantitatively indicated that the muscle activation caused by neural reflex is providing a protection for the neck in impact loading by decreasing the strain level and changing the possible injury to lower spinal cord level to reduce injury severity.

A Novel Neuromuscular Head-Neck Model and Its Application on Impact Analysis.

OBJECTIVE: Neck muscle activation plays an important role in maintaining posture and preventing trauma injuries of the head-neck system, levels of which are primarily controlled by the neural system. Thus, the present study aims to establish and validate a neuromuscular head-neck model as well as to investigate the effects of realistic neural reflex control on head-neck behaviors during impact loading. METHODS: The neuromuscular head-neck model was first established based on a musculoskeletal model by including neural reflex control of the vestibular system and proprioceptors. Then, a series of human posture control experiments was implemented and used to validate the model concerning both joint kinematics of the cervical spine and neck muscle activations. Finally, frontal impact experiments of varying loading severities were simulated with the newly established model and compared with an original model to investigate the influences of the implanted neural reflex controllers on head-neck kinematic responses. RESULTS: The simulation results using the present neuromuscular model showed good correlations with in-vivo experimental data while the original model even cannot reach a correct balance status. Furthermore, the vestibular reflex is noted to dominate the muscle activation in less severe impact loadings while both vestibular and proprioceptive controllers have a lot of effect in higher impact loading severity cases. CONCLUSIONS: In summary, a novel neuromuscular head-model was established and its application demonstrated the significance of the neural reflex control in predicting in vivo head-neck responses and preventing related injury risk due to impact loading.

In vitro compressive properties of skeletal muscles and inverse finite element analysis: Comparison of human versus animals.

Virtual finite element human body models have been widely used in biomedical engineering, traffic safety injury analysis, etc. Soft tissue modeling like skeletal muscle accounts for a large portion of a human body model establishment, and its modeling method is not enough explored. The present study aims to investigate the compressive properties of skeletal muscles due to different species, loading rates and fiber orientations, in order to obtain available parameters of specific material laws as references for building or improving the human body model concerning both modeling accuracy and computational cost. A series of compressive experiments of skeletal muscles were implemented for human gastrocnemius muscle, bovine and porcine hind leg muscle. To avoid long-time preservation effects, all experimental tests were carried out in 24 h after that the samples were harvested. Considering computational cost and generally used in the previous human body models, one-order hyperelastic Ogden model and three-term simplified viscoelastic quasi-linear viscoelastic (QLV) were selected for numerical analysis. Inverse finite element analysis was employed to obtain corresponding material parameters. With good fitting records, the simulation results presented available material parameters for human body model establishment, and also indicated significant differences of muscle compressive properties due to species, loading rates and fiber orientations. When considering one-order Ogden law, it is worthy of noting that the inversed material parameters of the porcine muscles are similar to those of the human gastrocnemius regardless of fiber orientations. In conclusion, the obtained material parameters in the present study can be references for global human body and body segment modeling.