Finite Element Analysis of Horizontal Screw-Screw Crosslink Used in C1-C2 Pedicle Screw-Rod Fixation

BACKGROUND In the craniocervical junction, a C1-C2 pedicle screw-rod (PSR) fixation is applied to provide stability. The horizontal rod-rod crosslink (hR-R CL) is often used to enhance segmental posterior instrumentation. However, the biomechanics of the alternative horizontal screw-screw crosslink (hS-S CL) in the craniocervical junction are unclear. MATERIAL AND METHODS A nonlinear atlantoaxial instability 3-dimensional C1-C2 finite element model was constructed using computed tomography images. On this basis, 2 fixation models were established with C1-C2 PSR fixation using (1) a rod-rod crosslink (R-R CL), and (2) a screw-screw crosslink (S-S CL). Range of motion (ROM) of the atlantoaxial joint, stress distribution of the implants, and maximum stress value of the vertebral bodies were calculated and compared under 4 loading conditions, including flexion, extension, lateral bending, and axial rotation. RESULTS Atlantoaxial joint ROM was reduced by 90.19% to 98.5% with the hR-R CL, and by 90.1% to 98.7% with the hS-S CL, compared with the instability model. During axial rotation, the total stress peak of the PSR fixation was smaller with hS-S CL than with hR-R CL. The peak stress values of the vertebral bodies were comparable between the 2 fixation models. CONCLUSIONS The 2 tested crosslink models provided comparable stability. However, during axial rotation, the total stress peak of hS-S CL fixation was smaller than that of hR-R CL fixation. Since the atlantoaxial joint primarily functions as a rotational joint, our results suggested that the use of hS-S CL can provide a more stable environment for the implants.

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