Finite element analysis of biomechanical changes in occipitocervical junction caused by atlanto-occipitocervical fusion and/or C2/3 fusion in Klippel-Feil syndrome

English Keywords:Klippel-Feil syndrome  Occipitalization of the atlas  C2/3 fusion  Sandwich deformity  Biomechanical  Finite element analysis

English Abstract:

  【Abstract】 Objectives: To assess the biomechanical kinematic and load alterations due to occipitalization of the atlas (OA) and/or C2/3 fusion in patients with Klippel-Feil syndrome (KFS). Methods: A 44-year-old healthy male volunteer was selected and the cervical spine was scanned by thin-slice spiral CT in our hospital. A nonlinear C0-C3 upper cervical spine three-dimensional finite element (FE) model (intact upper cervical spine model, INT model) was developed based on the CT scans using the software of Mimics, Geomagic Studio, SolidWorks, and ANSYS17.0. The validated INT model was altered to include the C2/3 fusion model (C2-3 model), OA model, and Sandwich deformity (SD) model (both OA and C2/3 fusion in one patient). The effect of different segments of fusion under different loading (1.2Nm, 1.5Nm, 1.8Nm, and 2.1Nm) on the range of motion (ROM) of C0-C1, C1-C2, C2-C3, and C0-C3 segment, maximum Von Mises stress in the transverse ligament and facet of atlantoaxial articulation were examined. Results: Compared with the INT model, the KFS model (including C2-3 model, OA model and SD model) resulted in a reduction of overall C0-C3 ROM and an overstress of the transverse ligament and bilateral atlantoaxial joints under the four kinds of physiological loading. The ROM of cervical flexion decreased 41.2%-49.2% by SD model, 33.8%-42.9% by OA model and 14.6%-19.2% by C2-3 model, and the ROM of extension decreased 39.8%-48.2%, 29.5%-35.1%, and 16.3%-30.4%, respectively. The ROM of rotation decreased 20.7%-28.0% by SD model, 10.4%-20.3% by OA model and 17.3%-34.2% by C2-3 model, and the ROM of lateral bending decreased 50.8%-56.1%, 40.8%-51.9%, and 23.2%-42.6%, respectively. Compared with the INT model, the stress of the transverse ligament and atlantoaxial joints increased most significantly in the SD model, by 65.5% and 123.1% respectively in the flexion and extension loading; which was followed by the OA model, by increasing 45.5% and 38.5% respectively; and that in the C2-3 model came the last, by increasing 18.2% and 15.4%. The transverse ligament stress of SD model, C2-3 model, and OA model increased respectively by 24.1%, 12.7%, and 5.1% in rotation loading, and increased by 206.7%, 166.7%, and 140.0% in lateral bending loading. The atlantoaxial joint stress of SD model, OA model, and C2-3 model increased by 193.0%, 150.0%, and 56.0% respectively in the extension loading; increased by 63.5%, 39.2%, and 16.4% in the rotation loading and 204.3%, 65.2%, and 160.8% in bending loading, respectively. Conclusions: The atlantooccipital fusion and/or C2/3 fusion can significantly increase the stress of the transverse ligament and facet of atlantoaxial articulation while limiting the ROM of the upper cervical spine, with different biomechanical kinematic in different number and different fused segments in the upper cervical spine.