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Introduction: Previous studies of bone stresses in the human lumbar spine have relied on simplified models
when modeling the spinal musculature, even though muscle forces are likely major contributors to the stresses in the
vertebral bones. Detailed musculoskeletal spine models have recently become available and show good correlation with
experimental findings. A combined inverse dynamics and finite element analysis study was conducted in the lumbar spine
to investigate the effects of muscle forces on a detailed musculoskeletal finite element model of the 4th lumbar vertebral
Materials and Methodology: The muscle forces were computed with a detailed and validated inverse dynamics
musculoskeletal spine model in a lifting situation, and were then applied to an orthotropic finite element model of the 4th
lumbar vertebra. The results were compared with those from a simplified load case without muscles.
Results: In general the von Mises stress was larger by 30 %, and even higher when looking at the von Mises stress
distribution in the superio-anterior and central part of the vertebral body and in the pedicles.
Conclusion: The application of spine muscles to a finite element model showed markedly larger von Mises stress
responses in the central and anterior part of the vertebral body, which can be tolerated in the young and healthy spine, but
it would increase the risk of compression fractures in the elderly, osteoporotic spine.