Updated: 1/22/2018

Structural Properties

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https://upload.orthobullets.com/topic/9061/images/Rigidity_moved.jpg
Introduction
  • Charateristics of orthopaedic implants depend
    • structural properties (this topic)
    • material properties
  • Structural characteristic differs from strength characteristic
    • not only depends on the material, but also the structural configuation of the object (cylinder, rectangle)
    • the stuctural properties can also be demonstrated in a stress vs. strain curve
Bending Rigidity (stiffness)
  • Definitions
    • defined as the slope of the curve in the elastic range on a structure stress-strain curve
    • stress shielding of proximal bone in THA is related to implant stem stiffness
  • Solid Cylinder 
    • proportional to the radius to 4th power for a solid cylinder
    • cylinder A has great rigidity than cyliner B on illustration above (and thus has greater radius)
  • Hollow Cylinder 
    • proportional to the radius to the 3rd power for a hollow cylinder
  • Rectangular Object
    • proportional to the (base x height) to the 3rd power
Area Moment of Inertia (I)
  • Closely related to bending rigidity
    • area moment of inertia is a function of: structure width, thickness, and polar moment of inertia (J)
      • polar moment of inertia represents an object resistance to torsion
Deflection
  • Proportional to: (applied force/elastic modulus)(area moment of inertia)
 

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