Finite element analysis of the effect on the stress of fusion segment by fixation combining lumbar cortical bone screw and pedicle screw

English Keywords:Cortical bone trajectory screw  Pedicle screw  Lumbar fusion  Finite element analysis  Biomechanics

English Abstract:

  【Abstract】 Objectives: We aimed to analyze the effect of the combined application of lumbar cortical bone trajectory screw(CBTS) and pedicle screw(PS) on the stress of fusion segment using three-dimensional finite element method. Methods: Lumbar CT data was collected from a healthy adult. The finite element method was applied tosimulate the lumbar fusion(L3/4) models, including PS fixation(group A), CBTS fixation(group B), and CBTS and PS combined fixation(group C). The lower surface of the L5 vertebral body was fixed, and 7.5N·m torque was applied to the model to simulate spinal flexion, extension, lateral flexion and rotation under physiological load. Range of motion(ROM) at L3/4 level was measured under physiological movement, and the stress peaks of internal fixation, interbody fusion device and interbody bone grafting were analyzed. Results: The stress of screw and connecting rod of group B and group C increased significantly comparing with that in group A in the 6 motion dimensions of the lumbar spine. During flexion, comparing with that in group A, the L3 screw stress increased by 84.7% in group B and 79.7% in group C. During extension, the stress of L3 screw in group C increased by 47.7% and 46.3% comparing with that in groups A and B, respectively. In left flexion, the stress of L3 screw in group C increased by 72.5% and 30.5% comparing with that in groups A and B. In right flexion, the stress of L3 screw in group C increased by 71.9% and 30.0% comparing with that in groups A and B. During flexion, comparing with that in group A, the L4 screw stress increased by 11.6% in group B and 18.9% in group C. During extension, comparing with that in group A, L4 screw stress increased by 40.1% in group B and 109.3% in group C. During rotation, screws stress of L3 and L4 in group C increased by 37.9% and 1.4% comparing with that in groups A and B. In left flexion, the stress of connecting rod in group C increased by 48.8% and 13.0% comparing with that in groups A and B. In the right flexion, the stress of connecting rod in group C increased by 8.8% and 4.9% comparing with that in groups A and B. The total stresses of Cage in the three groups were 318.8MPa, 319.6MPa, and 311.4MPa respectively. Group B had the smallest ROM in flexion and extension, and the largest ROM in lateral flexion and lateral rotation. Conclusions: CBTS fixation can increase the mechanical strength of the internal fixation structure of the lumbar fusion segment. The combined application of CBTS and PS can further increase the mechanical stability of the surgical segment while obtaining a similar stress environment for intervertebral fusion.