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Published byMckayla Littleton Modified over 10 years ago
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Orthopedic Biomechanics 沈文哲 台灣 高雄市 博正醫院
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Course Objectives Why are we studying this? Terminology Understanding the condition Management of fractures Design and application of implants
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Stress Strain Curve Strain
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Load Deformation Curve
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Creep
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Tension band Converts tension forces into compression forces
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Which is Strongest? How many twists are needed?
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Which hand do you hold the cane? 1) Rt side 2) Left side 3) No difference 4) Depends on the lumbar spine status Osteonecrosis Rt hip is painful
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The Non-Painful Side
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Which leg goes first when climbing stairs? Rt knee is painful
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好腳上天堂, 壞腳下地獄 Painful knee kept straight.
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Which brace to order?
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Think of the Forces 3-point fixation
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Where to place the knot? Submandibular position “long drop” 83kg – 173 cm 51kg – 244 cm hyperextension distraction
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Deforming Forces
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Fracture Patterns AO classification (Muller)
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Different Forces
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Classification Based on Mechanism of Injury Allen classification of cervical spine injuries
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Plate Fixation 6 wks3 mo1 yr
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A Load Bearing Construct 1 mo12 mo
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How long a plate? What kind of screw? Lag screw
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What angle? Where to put the plate?
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Placement of Implant
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How long? How thick? Titanium? Solid? Cross section? Fluted? Tapered? Bowing? Reaming? Interlocking? Cost!
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Stress risers Removal?
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Load Sharing and Stress Shielding Re-fracture
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Wolff’s Law Bone deposits along lines of stress transmission
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External Fixators Rubber band
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Fixator Design
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Hip Screws Gamma nail
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Choice of Implant
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Hip Prosthesis
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Choices of Stem
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Modularity
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Knee Prosthesis
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“ 軟骨凸出壓迫神經 ”
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Rank the intradiscal pressures Bending forward at waist Squatting Sitting Standing Supine
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Herniated Disc
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How big can you make the hole? 1) 75% of lamina 2) 50% of lamina 3) 75% of facet 4) 50% of facet 5) 25% of facet
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Spondylolisthesis Reduction flexion
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Missing Anterior Strut
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Fatigue Failure of the Screw
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Fusion Cage 椎籠 “ 子彈 ” Anterior Strut Only
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Does Not Resist Extension Forces
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40% Failure Rate Biomechanically, an anterior strut requires posterior support. “Supported on two rollers”
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Combined Ant/Post Fusion
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Stress Transfer 6 wks post-op 2 yrs post-op
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13+2 ♀ Menarche: 6 mo Risser II
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13+2 ♀ 7
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3-D Vector Analysis Instrumentation design Translate or Rotate?
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13+2 ♀
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Thank You!
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