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  • Title: Does location of rotation center in artificial disc affect cervical biomechanics?
    Author: Mo Z, Zhao Y, Du C, Sun Y, Zhang M, Fan Y.
    Journal: Spine (Phila Pa 1976); 2015 Apr 15; 40(8):E469-75. PubMed ID: 25868102.
    Abstract:
    STUDY DESIGN: A 3-dimensional finite element investigation. OBJECTIVE: To compare the biomechanical performances of different rotation centers (RCs) in the prevalent artificial cervical discs. SUMMARY OF BACKGROUND DATA: Various configurations are applied in artificial discs. Design parameters may influence the biomechanics of implanted spine. The RC is a primary variation in the popular artificial discs. METHODS: Implantation of 5 prostheses was simulated at C5-C6 on the basis of a validated finite element cervical model (C3-C7). The prostheses included ball-in-socket design with a fixed RC located on the inferior endplate (BS-FI) and on the superior endplate (BS-FS), with a mobile RC at the inferior endplate (BS-MI), dual articulation with a mobile RC between the endplates (DA-M), and sliding articulation with various RCs (SA-V). The spinal motions in flexion and extension served as a displacement loading at the C3 vertebrae. RESULTS: Total disc replacements reduced extension moment. The ball-in-socket designs required less flexion moment, whereas the flexion stiffness of the spines with DA-M and SA-V was similar to that of the healthy model. The contributions of the implanted level to the global motions increased in the total disc replacements, except in the SA-V and DA-M models (in flexion). Ball-in-socket designs produced severe stress distributions in facet cartilage, whereas DA-M and SA-V produced more severe stress distribution on the bone-implant interface. CONCLUSION: Cervical stability was extremely affected in extension and partially affected in flexion by total disc replacement. With the prostheses with mobile RC, cervical curvature was readjusted under a low follower load. The SA-V and BS-FS designs exhibited better performances in the entire segmental stiffness and in the stability of the operative level than the BS-MI and BS-FI designs in flexion. The 5 designs demonstrated varying advantages relative to the stress distribution in the facet cartilages and on the bone-implant interface. LEVEL OF EVIDENCE: 5.
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