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Optimization of Valgus Anatomy Angle of the Fractured Hip for Overcoming the Bone Unhealing Due to Increased Shear Stress at the Fixation Site, Considering Patient Bone Characteristics

Rastegar Talzali, Sajjad | 2012

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 43374 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Firoozbakhsh, Keikhosrow
  7. Abstract:
  8. In femoral neck fracture when the non-union happens in the fractured zone, valgus osteotomy is a surgery method to overcome bone non-union. In this method, a wedge osteotomy-with specific depth and angle- at the femoral neck is created. By changing the bone angle at the fracture site and the angle of the wedge osteotomy it is desired to convert the shear stress to the normal stress. Clinically it is believed that this would facilitate bone healing and prevent bone fracture. This surgery method also changes the anatomy of muscles due to changing hip anatomy, joint reaction force , and it’s direction. This procedure while minimizing shear stress it also reduces the blood supply to the area and therefore requires an optimum design for valgus osteotomy. Clinically with has been shown that for young patients, the excess normal pressure at the fractured zone can produce bone remodeling and help healing, however for older patients or in osteoporosis cases this may cause bone re-fracture. In this project first, the geometry of muscles and bone before and after valgus surgery was investigated. Consequently, muscle forces before and after valgus surgery has been calculated. By converting QCT of 8 patient femur data to our finite element model and then loading this model for fresh and osteotomized bone, a mathematical relation named constrain function was developed. Under specific assumptions, a general model function of shear stress was introduced and was named “aim function.” Lagrange optimization approach was used to make a robust method to estimate optimized values for valgus osteotomy. Our results demonstrated 13% error from the average data reported by Dr Alami Harandi and 15% error from the average data reported by Mango et al.
  9. Keywords:
  10. Shear Stress ; Lagrangian Optimization ; Femoral Neck Fracture ; Valgus Osteotomy

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