Biomechanics of the upper cervical spine ligaments in axial rotation and flexion-extension: Considerations into the clinical framework

CONTEXT: The motion of the upper cervical spine (UCS) has a great interest for analyzing the biomechanical features of this joint complex, especially in case of instability. Although investigators have analyzed numerous kinematics and musculoskeletal characteristics, there are still little data available regarding several suboccipital ligaments such as occipito-atlantal, atlantoaxial, and cruciform ligaments. OBJECTIVE: The aim of this study is to quantify the length and moment arm magnitudes of suboccipital ligaments and to integrate data into specific 3D-model, including musculoskeletal and motion representation. MATERIALS AND METHODS: Based on a recent method, suboccipital ligaments were identified using UCS anatomical modeling. Biomechanical characteristics of these anatomical structures were assessed for sagittal and transversal displacements regarding length and moment arm alterations. RESULTS: Outcomes data indicated length alterations >25% for occipito-atlantal, atlanto-axial and apical ligaments. The length alteration of unique ligaments was negligible. Length variation was dependent on the motion direction considered. Regarding moment arm, larger magnitudes were observed for posterior ligaments, and consistent alteration was depicted for these structures. CONCLUSION: These outcomes supply relevant biomechanical characteristics of the UCS ligaments in flexion-extension and axial rotation by quantifying length and moment arm magnitude. Moreover, 3D anatomical modeling and motion representation can help in the process of understanding of musculoskeletal behaviors of the craniovertebral junction.