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BACKGROUND: The cannulated lag screw technique has many advantages in the treatment of spondylolysis, but there is still the risk of fracture and loosening of the internal fixation. OBJECTIVE: To analyze the biomechanical stability of cannulated lag screw treatment of spondylolysis by establishing L4-S normal model, spondylolysis model and cannulated lag screw treatment model of spondylolysis through three-dimensional finite element software. METHODS: One male healthy young soldier volunteer was selected. 3D CT scan was performed on the volunteer’s lumbar spine and sacral spine. The imaging data were obtained and saved in Dicom format. CT data were imported into Mimics research 21.0 software to initially establish a geometric model, and deviation analysis was carried out. The obtained model was output in STEP format. Three groups of models of normal L4-S segment, L5 bilateral isthmus and cannulated lag screw in the treatment of spondylolysis were established after imported into Solidworks 21.0 software. They were represented by A, B and C respectively. The biomechanical characteristics of the three groups of models were compared under five motion states, such as axial compression, flexion, extension, left bending, and left rotation. RESULTS AND CONCLUSION: (1) Compared with models A and C, model B had the largest overall maximum displacement under the five working conditions of axial compression, flexion, extension, left bending, and left rotation. However, the overall maximum displacement of models A and C was not significantly different. (2) After removing the internal fixation in the model C, the maximum stress trend was similar to the model A. The stress of the model B was significantly higher than that of the models A and C during left bending and left rotation. (3) The overall maximum rotation angle of the three groups of models showed that the maximum rotation angle of the model B under the five working conditions was significantly larger than that of the models A and C. The models A and C were similar. The range of motion of the L4 vertebral body in the three groups did not change significantly. The range of motion of the L5 vertebral body in the model B was significantly higher than that in the models A and C, and it was more obvious in the left rotation and left bending. (4) These findings indicate that under the condition of physiological movement of the spine, the change trend of cannulated lag screw in the treatment of lumbar spondylolysis model is the same as that of normal model, which obtains good biomechanical stability and retains the normal mechanical characteristics of the spine, but excessive extension and rotation should be avoided immediately after operation. BACKGROUND: The cannulated lag screw technique has many advantages in the treatment of spondylolysis, but there is still the risk of fracture and loosening of the internal fixation. OBJECTIVE: To analyze the biomechanical stability of cannulated lag screw treatment of spondylolysis by establishing L4-S normal model, spondylolysis model and cannulated lag screw treatment model of spondylolysis through three-dimensional finite element software. METHODS: One male healthy young soldier volunteer was selected. 3D CT scan was performed on the volunteer’s lumbar spine and sacral spine. The imaging data were obtained and saved in Dicom format. CT data were imported into Mimics research 21.0 software to initially establish a geometric model, and deviation analysis was carried out. The obtained model was output in STEP format. Three groups of models of normal L4-S segment, L5 bilateral isthmus and cannulated lag screw in the treatment of spondylolysis were established after imported into Solidworks 21.0 software. They were represented by A, B and C respectively. The biomechanical characteristics of the three groups of models were compared under five motion states, such as axial compression, flexion, extension, left bending, and left rotation. RESULTS AND CONCLUSION: (1) Compared with models A and C, model B had the largest overall maximum displacement under the five working conditions of axial compression, flexion, extension, left bending, and left rotation. However, the overall maximum displacement of models A and C was not significantly different. (2) After removing the internal fixation in the model C, the maximum stress trend was similar to the model A. The stress of the model B was significantly higher than that of the models A and C during left bending and left rotation. (3) The overall maximum rotation angle of the three groups of models showed that the maximum rotation angle of the model B under the five working conditions was significantly larger than that of the models A and C. The models A and C were similar. The range of motion of the L4 vertebral body in the three groups did not change significantly. The range of motion of the L5 vertebral body in the model B was significantly higher than that in the models A and C, and it was more obvious in the left rotation and left bending. (4) These findings indicate that under the condition of physiological movement of the spine, the change trend of cannulated lag screw in the treatment of lumbar spondylolysis model is the same as that of normal model, which obtains good biomechanical stability and retains the normal mechanical characteristics of the spine, but excessive extension and rotation should be avoided immediately after operation. [ABSTRACT FROM AUTHOR]

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