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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