Abstract
BackgroundThe biomechanics of C1 posterior arch screw and C2 vertebral lamina screw techniques has not been well studied, and the biomechanical performance of the constructs cannot be explained only by cadaver testing.MethodsFrom computed tomography images, a nonlinear intact three-dimensional C1-2 finite element model was developed and validated. And on this basis, models for the odontoid fractures and the three posterior internal fixation techniques were developed. The range of motion (ROM) and stress distribution of the implants were analyzed and compared under flexion, extension, lateral bending, and axial rotation.ResultsAll three kinds of fixation techniques completely restricted the range of motion (ROM) at the C1-2 operative level. The C1-2 pedicle screw fixation technique showed lower and stable stress peak on implants. The C1 posterior arch screw + C2 pedicle screw and C1 pedicle screw + C2 lamina screw fixation techniques showed higher stress peaks on implants in extension, lateral bending, and axial rotation.ConclusionsAs asymmetrical fixations, C1 posterior arch screw + C2 pedicle screw and C1 pedicle screw + C2 lamina screw fixations may offer better stability in lateral bending and axial rotation, but symmetrical fixation C1-2 pedicle screw can put the implants in a position of mechanical advantage.
Highlights
The biomechanics of C1 posterior arch screw and C2 vertebral lamina screw techniques has not been well studied, and the biomechanical performance of the constructs cannot be explained only by cadaver testing
In comparison with the C1 pedicle screw (C1PS) + C2 pedicle screw (C2PS) model, the C1 posterior arch screw (C1PAS) + C2PS model increased the range of motion (ROM) by 4.7% and 23.1% in flexion and extension, respectively, and reduced the ROM by 29.9% and 15.8% in lateral bending and axial rotation, respectively; the ClPS + C2 lamina screw (C2LS) model reduced the ROM by 3.7%, 26.4%, and 29.6% in flexion, lateral bending, and axial rotation, respectively, and increased the ROM by 28.6% in extension
Implants of all constructs had the maximum stress in extension among the four loading conditions; stress peaks of C1PS + C2PS, C1 posterior arch screw (ClPAS) + C2PS, and ClPS + C2LS models were 45.94 MPa, 97.69 MPa, and 77.34 MPa, respectively (Fig. 4)
Summary
The biomechanics of C1 posterior arch screw and C2 vertebral lamina screw techniques has not been well studied, and the biomechanical performance of the constructs cannot be explained only by cadaver testing. Liu et al Journal of Orthopaedic Surgery and Research (2020) 15:156 To address these concerns, C1 posterior arch screw (C1PAS) fixation and C2 lamina screw (C2LS) fixation have been emerging as a useful stabilization technique in recent years. In 2013, Guo-Xin et al [10] designed C1 posterior arch crossing screw fixation both to avoid disturbing the heads and to increase the lengths of the screws They studied its feasibility on the basis of anatomical measurements and in vitro biomechanical testing. Some in vitro testing and short-term follow-up studies showed that the C2 laminar screw fixation provides equal stiffness to the pedicle screw fixation [12, 14, 15] These constructs posed no risk of injury to the vertebral artery (VA) and were further shown to be a good alternative in clinical practice
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