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Biomechanical differences between occipital plate and modified C1 lateral mass screw in the treatment of complex
Chenpeng Dong1, Zhiqiang Xu2, Xintong Ran3
1Department of Orthopaedics, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China.
Background:
Complex craniocervical malformations pose significant challenges to surgical fixation. The biomechanical advantage of occipital plate fixation versus short-lever modified C1 lateral mass screw fixation remains controversial, and finite element analysis (FEA) is a reliable tool for implant performance evaluation.
Objective:
To compare biomechanical characteristics of occipital plate fixation and modified C1 lateral mass screw fixation in AOZ-BI and AOZ-AAD models via FEA, and guide surgical decision-making.
Methods:
A validated healthy occipito-atlantoaxial (C0-C2) FEA model was established using CT data. Two pathological models were constructed: AOZ-BI (Group A, atlantoaxial distance [ADI] < 5 mm) and AOZ-AAD (Group B, ADI ≥ 5 mm with transverse ligament dysfunction), each divided into occipital plate and modified C1 lateral mass screw subgroups. Static loads (40 N preload + 1.5 N·m torque) simulated flexion (Fe), extension (Ex), lateral bending (LB), and axial rotation (AR). C1-C2 range of motion (ROM) and screw-rod peak Von Mises stress (PVMS) were measured.
Results:
Modified C1 lateral mass screw fixation reduced C1-C2 ROM by 19.67% (flexion-extension) to 48.51% (lateral bending) compared with occipital plate fixation. In flexion/extension/axial rotation, C1 lateral mass screw fixation increased screw-rod peak Von Mises stress (PVMS) by 51.17%-131.37% in the AOZ-BI group and 36.51%-56.02% in the AOZ-AAD group; in lateral bending, PVMS decreased by 19.46% in the AOZ-BI group but increased by 5.24% in the AOZ-AAD group. occipital plate fixation consistently had higher ROM (Group B highest) but lower PVMS.
Conclusions:
Modified C1 lateral mass screw fixation provides superior C1-C2 stability for AOZ-associated BI-AAD but increases implant stress in Fe/Ex/AR. Occipital plate fixation is less stable but reduces stress. Clinically, C1 lateral mass screw is preferred for AOZ-BI; AOZ-AAD requires balancing stability and stress risk. Occipital plate suits patients with severe C1 lateral mass hypoplasia. FEA effectively evaluates craniocervical fixation biomechanics.
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