Biomechanical differences of three cephalic fixation methods for patients with basilar invagination and atlantoaxial dislocation in the setting of congenital atlas occipitalization: a finite element analysis

Qiang Jian; Shaw Qin; Zhe Hou; Xingang Zhao; Yinqian Wang; Cong Liang; Dean Chou; Xiuqing Qian; Tao Fan

doi:10.1016/j.spinee.2024.08.023

Biomechanical differences of three cephalic fixation methods for patients with basilar invagination and atlantoaxial dislocation in the setting of congenital atlas occipitalization: a finite element analysis

Spine J. 2024 Sep 19:S1529-9430(24)00989-6. doi: 10.1016/j.spinee.2024.08.023. Online ahead of print.

Authors

Qiang Jian¹, Shaw Qin², Zhe Hou³, Xingang Zhao⁴, Yinqian Wang⁴, Cong Liang⁴, Dean Chou², Xiuqing Qian⁵, Tao Fan⁶

Affiliations

¹ Spine Center, Sanbo Brain Hospital, Capital Medical University, Beijing, 100093, China; Department of Neurological Surgery, The Och Spine Hospital at NewYork-Presbyterian, Columbia University, New York, 10034, NY.
² Department of Neurological Surgery, The Och Spine Hospital at NewYork-Presbyterian, Columbia University, New York, 10034, NY.
³ Spine Center, Sanbo Brain Hospital, Capital Medical University, Beijing, 100093, China; Department of Neurosurgery, Beijing Luhe Hospital, Capital Medica University, Beijing, 100020, China.
⁴ Spine Center, Sanbo Brain Hospital, Capital Medical University, Beijing, 100093, China.
⁵ School of Biomedical Engineering, Capital Medical University, Beijing, 100069, China; Beijing Key Laboratory of Fundamental Research on Biomechanics in Clinical Application, Capital Medical University, Beijing, 100069, China.
⁶ Spine Center, Sanbo Brain Hospital, Capital Medical University, Beijing, 100093, China. Electronic address: fant@ccmu.edu.cn.

PMID: 39306196
DOI: 10.1016/j.spinee.2024.08.023

Abstract

Background context: In cases of basilar invagination-atlantoaxial dislocation (BI-AAD) complicated by atlas occipitalization (AOZ), the approach to cranial end fixation has consistently sparked debate, generally falling into two categories: C1-C2 fixation and occipitocervical fixation. Several authors believe that C1-C2 fixation carries a lower risk of fixation failure than occipitocervical fixation.

Purpose: To study the biomechanical differences among 3 different cranial end fixation methods for BI-AAD with AOZ.

Study design: This was a finite element analysis.

Patient sample: A 35-year-old female patient diagnosed with congenital BI-AAD and AOZ.

Outcome measures: range of motion (ROM), peak von Mise stress (PVMS), cage micro-subsidence, cage micro-slippage METHOD: Four finite element models were constructed, including unstable group (BI-AAD with AOZ), C1 lateral mass screw group, occipital plate group, occipitocervical rod group. The flexion and extension (FE), lateral bending (LB) as well as axial rotation (AR) were simulated under a torque of 1.5 Nm. Parameters include C1-C2 ROM, PVMS on screw-rod construct, cage micro-subsidence, cage micro-slippage.

Results: The ROM of the C1 lateral mass screw group was smaller than that of the other fixation groups in LB and AR, but not FE. Compared with the occipitocervical rod group, the ROM in LB and AR of the occipital plate group was higher, but not in FE. The PVMS of C1 lateral mass screw group was significantly higher than that of the other groups. The ROM and PVMS of the occipitocervical rod group were in between the other 2 groups. Regarding the screws at the cranial end, the PVMS of the 4-screw occipitocervical rod group was significantly lower than that of the other groups. In general, the cage micro-motion follows the ascending order: C1 lateral mass group < occipitocervical rod group < occipital plate group.

Conclusion: In cases of BI-AAD with AOZ, the C1 lateral mass screw group provided the least ROM and cage micro-motion, but the screw-rod PVMS was the largest. The advantage of occipital plate fixation lies in the lowest screw-rod PVMS, but the ROM and cage micro-motion is the highest. Four-screw fixation at the cranial end of occipitocervical rod group helps to reduce the PVMS and may prevent screw failure at the cranial end.

Keywords: Atlantoaxial dislocation; Atlas occipitalization; Basilar invagination; Intra-articular cage; Micro-motion; Subsidence.