| Sumario: | Frequently, treatment decisions for craniocervical injuries and instability are based on imaging findings, but in vivo ligament kinematics were poorly understood. This study was to determine in vivo deformation patterns of primary ligaments in the craniocervical junction (i.e. , C0–2), including the cruciform ligament, alar ligaments, and accessory ligaments, during dynamic head axial rotation. The skulls and cervical spines of eight asymptomatic female subjects were dynamically imaged using a biplane fluoroscopic imaging system, when they performed left and right head axial rotations. Using a 3D-to-2D registration technique, the in vivo positions and orientations of cervical segments were determined. An optimization algorithm was implemented to determine ligament wrapping paths, and the resulting ligament deformations were represented by percent elongations. Using paired t -tests, ligament deformations in the end-range position were compared to those in the neutral position. No significant differences were observed in segmental motions during left and right head rotations (p > 0.05). In general, slight deformations occurred in each component of the cruciform ligament. For the alar ligaments, the ipsilateral ligament was lengthened from −0.7 ± 13.8% to 16.6 ± 15.7% (p < 0.001*). For the accessory ligaments, the contralateral ligament was lengthened from −2.9 ± 7.5% to 10.1 ± 6.2% (p < 0.001*). This study reveals that there are distinct deformation patterns in craniocervical junction ligaments during dynamic axial head rotation. These ligament deformation data can enhance our understanding of the synergic function of craniocervical junction ligaments, and guide the treatment of craniocervical instability. • Motions of the craniocervical junction during head rotation were measured. • Deformation patterns of the primary craniocervical ligaments were determined. • The cruciform ligament was marginally deformed. • The ipsilateral alar ligament and the contralateral accessory ligament were elongated. • Ligament deformation patterns can help diagnose craniocervical instability.
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