Comparative biomechanical analysis of pedicle screws versus cortical bone trajectory fixation in the treatment of ankylosing spondylitis

Abstract

Background Ankylosing spondylitis (AS) is an inflammatory rheumatic disease. Patients with spinal deformities are typically treated with long-segment pedicle screw (PS) internal fixation after bone resection. However, issues with the operation, such as fracture and screw loosening or pulling out, might arise. Methods This study explore the biomechanical responses to PS and cortical bone trajectory (CBT) fixation. Using finite element analysis (FEA) on reconstructed preoperative and postoperative spine models under six conditions, it predicted stiffness, range of motion (ROM), and von Mises stress, comparing PS and CBT fixation effects. Results Stiffness was greater in the PS than CBT, while the PS performed better than the CBT under bending stiffness, except for the PS under extension conditions. In flexion, extension, and lateral bending, the PS sustained higher stress than CBT, while in axial rotation, CBT experienced greater stress than PS, with stress concentration at the level of bone resection. Furthermore, during spinal dynamics, calcified ligaments bore substantial stress. Biomechanically, PS demonstrated superior strength during flexion, extension, and lateral bending conditions. Whereas, under conditions of left and right rotation, the CBT technique provided better biomechanical strength. Conclusion Compared to PS, the current CBT technique was sufficiently effective in maintaining spinal fusion stability after bone resection for AS.