Abstract: BACKGROUND: Finite element analysis based lumbar biomechanical modeling technology, because it can quantitatively assess the lumbar range of motion and disc and other structures of stress distribution characteristics, has become an important tool to study the mechanism of lumbar diseases and surgical plan optimization. At present, the common finite element models of lumbar spine include vertebrae, intervertebral discs, endplates, articular cartilage and ligaments. The existing finite element models of lumbar spine generally do not consider the effect of passive support of deep intrinsic muscle groups on the stability of lumbar spine segments.
OBJECTIVE: A finite element model of the lumbosacral musculoskeletal muscles containing the deep intrinsic muscle groups of the lumbar spine was established, and the biomechanical differences between the lumbosacral skeletal finite element model and the lumbosacral skeletal muscle finite element model were compared using finite element analysis.
METHODS: A finite element model of the lumbosacral spine skeleton was reconstructed based on CT data from a healthy volunteer aged 27 years, and the deep intrinsic lumbar muscle groups were reconstructed on this basis. The effect of passive support on lumbar spine was evaluated by finite element analysis of the changes of lumbar range of motion, intervertebral disc stress, and vertebral cortical bone stress after increasing passive support of lumbar deep intrinsic muscle groups at different working conditions.
RESULTS AND CONCLUSION: After applying the same load, under the combined conditions of forward flexion, extension, left and right lateral bending, left and right axial rotation, forward flexion and axial rotation: (1) Lumbar range of motion: The range of motion of lumbosacral musculoskeletal finite element model with passive muscle support was less than that of lumbosacral skeletal finite element model, and the more types of muscles, the smaller the range of motion. The range of motion of lumbosacral musculoskeletal model including lumbar intertransverse lateral muscles and lumbar circumflex muscles was less than that of lumbosacral skeletal finite element model, while the range of motion of lumbosacral musculoskeletal model including lumbar intertransverse lateral muscles, lumbar circumflex muscles and lumbar multifidus muscles was the smallest. (2) Intervertebral disc and vertebral cortical stress: In the lumbosacral skeletal finite element model, the addition of passive muscle support factors reduced the maximum stress values of the intervertebral disc and vertebral body, but their stresses showed a similar distribution, and the degree of stress reduction was related to the number of muscles, in which the lumbosacral musculoskeletal model including the lumbar intertransverse lateral muscles and lumbar circumflex muscles had smaller maximum stress values of the intervertebral disc and vertebral cortical bone than the lumbosacral skeletal finite element model, while the lumbosacral musculoskeletal model including the lumbar intertransverse lateral muscles, lumbar circumflex muscles and lumbar multifidus muscles had the smallest maximum stress values of the intervertebral disc and vertebral cortical bone. It is suggested that passive support of deep intrinsic muscles of lumbar spine slows down the range of motion, intervertebral disc stress and cortical bone stress of lumbar spine, especially under the conditions of forward flexion, extension, left and right lateral bending, forward flexion and axial rotation.

Key words: lumbar spine, muscle groups, model, finite element analysis, lumbar range of motion, intervertebral disc, cortical bone, stress