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Titanium vs. Stainless Steel
 

Stainless Steel

The standard material currently used for veterinary orthopedic implants is 316L stainless steel.  The 316L alloy consists of iron with lesser amounts of chromium (18%), nickel (14%), molybdenum (2.5%), manganese (2%) and traces of other elements.  Implants made from 316L stainless steel have been widely used by veterinary surgeons over the past 50 years.  Stainless steel is favored because it has good mechanical properties, it is easy to manufacture and it is well tolerated in most patients.  However, stainless steel has the disadvantages that is relatively heavy, is much stiffer than bone, and is not completely resistant to corrosion in biological settings.

Titanium

Pure titanium and titanium alloys have also been used for orthopedic implants.  In human patients, approximately 50% of the implants used for orthopedic surgery are made from titanium and titanium alloys.  Titanium and its alloys are graded by the American Society for Testing Material's standards (ASTM).  There are four grades of "pure" titanium and over 25 grades of titanium alloys.  Grade 4 unalloyed titanium offers a reasonably high strength, good workability and excellent resistance to corrosion.  Pure titanium is often preferred for bone plates because it is easier to contour (more ductile) than the titanium alloys. 

Titanium alloys made with aluminum and vanidium (Ti-6Al-4V) or aluminum and niobium (Ti-6Al-7Nb) are usually preferred for intramedullary rods, spinal clamps and self tapping screws because of their increased strength and excellent corrosion resistance.  Most titanium alloys have a higher tensil strength, higher yield strength and slightly higher modulus of elasticity than pure titanium.
 

Comparing Titanium with Stainless Steel

  • Medical grades of titanium have a significantly higher strength to weight ratio than stainless steel.
  • Titanium implants are light, weighing about 45% of comparably sized 316L stainless steel implants and yet the single load strength of Grade 4 Pure titanium is only about 10% less than that of stainless steel.
  • Titanium alloys have higher tensile and yield strengths than stainless steel.  With internal fixation, the resistance to repeated loads (cycling) is much more important than the ultimate faiure strength of the implant.
  • Compared to stainless steel, titanium has superior strength under the high cycle repeated load stresses encountered clinically with internal fixation.
  • Titanium and titanium alloys are not notch sensitve, which means that stress raisers have minimal effects on mechanical properties of titanium implants.
  • Titanium has a lower (approximately 50% less) modulus of elasticity than stainless steel.  A lower modulus of elasticity means that titanium is significantly less stiff than steel, which helps to minimize stress shieldng of bone.
  • Compared to bone, titanium is approximately 4-5 times stiffer and stainless steel is approximately 10 times stiffer.
  • Titanium is immune to fretting and local corrosion that is seen with stainless steel implants.
  • Titanium implants demonstrate negligible magnetism and causes less interference than stainless steel when scanned with Magnetic Resonance Imaging (MRI) equipment.