Biomechanical Study on Three Screw-Based Atlantoaxial Fixation Techniques: A Finite Element Study.

Area of Science:

• Biomechanical analysis of spinal fixation techniques.
• Finite element modeling of the upper cervical spine.
• Analysis of stress and strain in surgical constructs.

Background:

• Atlantoaxial joint stabilization commonly uses screw-based constructs.
• Existing studies compare fixation effectiveness but lack biomechanical stress/strain data.
• Understanding construct biomechanics is crucial for surgical success.

Purpose of the Study:

• To compare the biomechanical behaviors of three screw-based atlantoaxial fixation techniques.
• Evaluate the stability and stress distribution of different fixation methods.
• Identify potential failure points in atlantoaxial stabilization constructs.

Main Methods:

• Developed a finite element model of the upper cervical spine.
• Simulated a type II dens fracture to create an injured model.
• Modeled three constructs: transarticular (C1-C2TA), lateral mass/pedicle (C1LM1-C2PD), and lateral mass/translaminar (C1LM1-C2TL).

Main Results:

• All constructs significantly reduced range of motion (ROM) in flexion-extension, lateral bending, and axial rotation.
• C1LM1-C2TL construct experienced the highest maximum von Mises stress (332 MPa), followed by C1LM1-C2PD (307 MPa) and C11-C2TA (133 MPa).
• Maximum stress in C1LM1-C2TL was concentrated at the lateral mass screw head.

Conclusions:

• Translaminar screws (C1LM1-C2TL) demonstrate less reliable biomechanical stability in lateral bending compared to transarticular and pedicle screws.
• High stresses on translaminar screws may lead to construct failure before bony fusion.
• Transarticular and pedicle screw constructs offer superior biomechanical support for the atlantoaxial joint.