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Stainless Steel

- Discussion:
     - Characteristics of Metals and Implants:
     - has best mechanical properties, as it is strong and has good fatigue resistance;
     - it is easily worked and cheap to manufacture;
     - serious draw back is the tendency to corrode;
     - forged stainless steel has greater yield strength than cast stainless steel, but has lower fatigue strength than other alloys;
     - elastic modulus of stainless steel is 12 times EM of cortical (EM of titanium is 6 times of cortical bone)
     - w/ THR, because of femoral component fracture with early designs, stainless steel is no longer routinely used;
     - from the standpoint of erosion, biocompatibility, and fatigue life, stainless steel is inferior to other superalloys;

- Corrosion Properties:
    - corrodes more easily than other materials;
    - addition of chromium and molybdenum to stainless steel produces corrosive resistant surface layer;
            - chromium creates a protective self regenerating chromium oxide layer that protect against corrosion;
            - molybdenum decreases the rate of slow passive dissolution of chromium oxide layer by up to 1000 times
            - nickle provides additional corrosion resistance;
    - surfaces of all metal implants in the U.S. are covered using nitric acid to form an oxide or hydroxide on their surfaces;
    - fretting corrosion:
            - a process in which abrasive wear is accompanied by corrosion;
            - protective oxide layer on metal is removed by abrasion process;
            - because new passivation layer that forms after abrasion is neither as durable nor as chemically inert as original layer, metal is more 
                    susceptible to corrosion;
          - this form of corrosion often occurs between screw heads & plates;
          - stainless steel & cobalt-chromium alloys are susceptible to fretting corrosion

Original Text by Clifford R. Wheeless, III, MD.

Last updated by Clifford R. Wheeless, III, MD on Sunday, August 4, 2013 9:58 am