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Development and Validation of a Finite Element Model of the Occipito-Atlantoaxial Complex Under Physiologic Loads

Study Design. Numerical techniques were used to study the occipito-atlantoaxial complex. Objectives. To improve previous upper cervical spine finite element models and validate both the range of motion (ROM) and neutral zone of the model. Summary of Background Data. Finite element modeling is an important tool for studying the cervical spine. It has been theorized that the neutral zone may be a more sensitive parameter of spinal instability than ROM. However, the authors know of no published results by far that have validated the neutral zone of an occipito-atlantoaxial finite element complex. Methods. An anatomic detailed, nonlinear finite element model based on the Visible Human Male data set was developed in this study. ROM and the neutral zone were compared with published experimental data in the analysis of the motions of each vertebral level under physiologic static loadings to simulate the movements of upper cervical spine under axial rotation, flexion, extension, and lateral bending. In addition, the loads of each ligament were also recorded. Results. The moment-rotation relationship predicted by this model was apparently nonlinear, and the largest rotation was predicted in horizontal plane, followed by median plane and coronal plane. The ligaments across the complex were generally lax, and, therefore, the complex exhibited large ROMs and high proportions of the neutral zone to ROM. Conclusions. The findings from the validation of this newly developed model coincide with the experimental studies so that its application helps contribute to a more comprehensive understanding of the biomechanics of the craniocervical region.