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Estimation of Spinal Loads in Static Activities by Considering Trunk Muscle Forces in a Detailed Nonlinear Finite Element Model

Khodam Khorasani, Pooria | 2020

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 53292 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Arjmand, Navid; Shirazi-Adl, Aboulfazl
  7. Abstract:
  8. Spine biomechanical models suffers from either simplification in passive disc components modeling (modeling via torsional spring or beam elements) in musculoskeletal (MS) models or shortcomings in detailed muscles modeling (via a simple force and torque vector) in detailed finite element (FE) models. Considering these, that is aimed in this study to develop a hybrid MS-FE model which the calculated muscle forces by a MS model (developed based on geometrical and mechanical properties of FE model) for a desired static posture, being applied to a detailed FE model. Considering the change of discs stiffness in FE model under the applied muscles and gravity forces, the equivalent stiffness in MS model is modified in iterative procedure, until the FE model converges to reference posture under gravity and updated muscles forces (calculated by MS model with updated stiffness). Comparison of calculated L4-L5 intra-discal pressure and relative center of rotation for vertebrae with experimental measurements confirms our developed hybrid model estimations. It is shown that using a simple force and torque vector as a muscles and gravity forces simplification in current studies, concludes in remarkable load sharing estimation error by FE model. Furthermore, the estimated total segmental loads by MS model and disc loads by FE model necessarily do not replicate the same pattern and thus the importance of calculating load sharing by hybrid model is concluded. As an application of the hybrid model, three different load lifting lumbar postures including lordotic, free and kyphotic postures are compared to find the posture with the lowest damage risk. Calculating the load sharing between different components of segmental discs, first it is shown that despite of common beliefs, intra-discal pressure (1.8-3.4%) and maximum collagen fiber strain (0.4-4.7%) – as two important discs damage criteria - have no remarkable changes between different postures. Furthermore, results show an increase in segmental compression (7.5-46.1%), segmental shear (5.4-47.5%) and muscles activity (14-19%) for lordotic posture. Passive muscles and ligaments play a more important role in tolerating external loads in kyphotic posture (30-42%) comparing to lordotic posture (10-18%). Finally, considering the decrease in spinal stability in repetitive load lifting tasks for lordotic posture due to active muscle fatigue and in kyphotic posture as a consequence of creep in disc passive components, free posture is suggested as the optimal lumbar posture for load lifting tasks
  9. Keywords:
  10. Spine ; Muscles ; Intradiscal Pressure ; Hybrid Modeling ; Finite Element Model ; Musculoskeletal Modeling ; Disc Fiber Strain

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