Abstract

Objective.  The objective of this research was to develop a muscle-driven biomechanical model of the human head-neck system that could be used to simulate neck movements under muscle control.  This model can further be modified to enable input from an external stimulus, such as EMG data.

Summary of background data.  Utilizing computer aided design (CAD) and dynamic simulation software programs, the Joint Implant Biomechanics Laboratory at The University of Tennessee Health Science Center developed a virtual model of the human cervical spine to simulate the in vitro biomechanical experiments.  This in vitro model did not include any muscle components and was unable to simulate any active muscle contribution to head-neck movement.  However, the model served well as a platform from which to develop a dynamic musculoskeletal head-neck model that could include muscle involvement.

Methods.  The development of the current head-neck model was based on a previous in vitro model of the sub-axial cervical spine that was developed within the rigid body dynamic simulation program, Visual Nastran 4D.  Interconnecting joints, including intervertebral discs, facet joints, ligaments, and the C0-C1-C2 complex, were defined.  The primary neck muscles for axial rotation, lateral bending, extension, and flexion movements were defined, respectively.  For each specific movement, the model was driven by muscle length control using three different muscle sets: (1) all the inclusive primary muscles (“All muscles” mode), (2) only the primary muscles during a concentric contraction (“Concentric contraction muscles only” mode), and (3) only the primary muscles during an eccentric contraction (“Eccentric contraction muscles only” mode).  The simulation results obtained from these three modes were compared to the in vivo published data.

Results.  Simulation results from the muscle model for axial rotation and flexion were comparable to the in vivo data in each of the three muscle mode sets.  For extension and lateral bending movement, only the results from the “All muscles” mode matched the in vivo data.  There were no significant translations that occurred in the upper cervical spine region, which was in agreement with the published literature.

Concluding discussion.  A computational model of the human head-neck musculoskeletal system was developed that simulated the dynamic motion response under physiologic head movements.  The motion-driven model provided excellent replication of in vivo vertebral kinematics.  A similar response occurred for the muscle-driven model when the groups on both sides were activated.  Although there was no significant involvement of the extensor muscles during flexion, the forward flexor muscles played an important role during extensional head movement.  In the future, the model can be used to explore muscle control strategies within the “Virtual Muscle” program to simulate EMG muscle force activation conditions. 

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Revised 06 June 2006