Biomechanical mechanisms of manipulative reduction for pediatric type II atlantoaxial subluxation a finite element analysis with neurocentral synchondroses

To establish and validate a 6-year-old pediatric craniocervical finite element model that includes the neurocentral synchondrosis (NCS), to construct a type II atlantoaxial subluxation (AAS) model, and to identify high-risk structures during simulated rotational manipulation, thereby providing biomechanical evidence for the safety of manipulative treatment for pediatric AAS. A three-dimensional C0–T1 finite element model was constructed from CT data of a healthy 6-year-old child. The NCS were manually segmented and incorporated. Material properties were assigned based on pediatric literature. Model validation was performed by comparing segmental range of motion under a 1.5 N·m pure moment with published cadaveric data. A type II AAS model was created by anterior translation of the atlas to achieve an atlantodental interval (ADI) of 4.0 mm. Von Mises stress changes were analyzed under six loading conditions (flexion, extension, lateral bending, rotation). A clinical rotational manipulation was simulated to identify regions of stress concentration. The model showed good agreement with the cadaveric data of Panjabi et al. Compared with the normal model, the type II AAS model exhibited: (1) significantly reduced range of motion at all levels, most notably in C1–C2 rotation; (2) increased stress in all cervical structures, with a 50.5% increase in peak flexional stress at C2 (3.29 → 4.95 MPa); (3) an 8.0% increase in synchondrosis stress during extension (1.63 → 1.76 MPa); and (4) high-stress areas during rotational manipulation involving the capsular ligament (3.09 MPa), transverse ligament (2.37 MPa), odontoid process, C1 lateral mass (4.08 MPa), and C2 pedicle (4.05 MPa). A pediatric craniocervical finite element model incorporating the synchondrosis and a type II AAS model were successfully established and validated. AAS leads to compensatory increased mechanical loading throughout the entire cervical spine, presenting a “chain effect”. The transverse ligament, capsular ligament and odontoid process are high-risk structures during rotational manipulation. This model provides a biomechanical platform for parameter optimization and risk assessment of manipulative reduction for pediatric AAS.