Abstract: BACKGROUND: Paravertebral muscles play an important role in maintaining spinal balance. The finite element model of skeletal muscle is more close to the biomechanical environment of human body. However, the muscle modeling in the finite element analysis of the spine is more complex or the muscle force is simplified in the current finite element analysis of the spine.  
OBJECTIVE: To quickly establish the paravertebral muscle model and analyze loading of muscle force.
METHODS:  Based on the principle of reverse engineering, the three-dimensional reconstruction of the spine model was carried out through CT image data. The spring stiffness of the longest lumbar muscle and ligament in the erector spinalis muscle was calculated through the elastic modulus, muscle cross-sectional area and average length of muscle line. The muscle modeling was carried out through the upper and lower attachment points, and the biomechanical verification of the established finite element model was carried out. The lumbar spine was simulated by applying a bending moment of 4 N•m for flexion and extension, left and right lateral bending, left and right rotation.  
RESULTS AND CONCLUSION: (1) Biomechanical verification showed that L4-L5 showed elastic properties under axial load. (2) Through the analysis of lumbar flexion and extension, left-right lateral bending and left-right rotation, a finite element model of skeletal muscle was established, which was consistent with the range of motion of lumbar spine. (3) The finite element model of lumbar spine with muscle tissue conforms to the biomechanical characteristics of human body, which provides a reference for analyzing the changes of the spine under orthopedic force.

Key words: lumbar spine, biomechanics, skeletal muscle model, CT data, image segmentation, reverse engineering, finite element