Stainless Steel , Titanium and Cobalt-Chrom

Candidate:

Stainless steel used in orthopedic implants is known as 316L, which consists of 60% iron, 20% chromium, 3% molybdenum, 16% nickel, and a low carbon content of 0.03%. Steel typically comprises carbon and iron, but the addition of more than 4% chromium turns it into stainless steel.

Candidate:

There are several ways to manufacture stainless steel for orthopedic use. The first method is casting, which involves pouring molten metal into a mold to create the desired shape. Another method is wrought, which involves rolling and shaping the cast metal. Cold working, which involves rolling the metal at room temperature, can increase the ultimate tensile strength (UTS) of the metal but also makes it more brittle. Annealing, which involves heating the metal to about half of its melting temperature, makes the metal more ductile and workable. Hot working, which involves heating the metal to about 60% of its melting point while it is working, can increase its ductility. Alloying is another method that involves adding other elements to the steel to change its properties. Quenching is immersing the hot metal in cold water or oil to reduce crystal grain size and increase hardness. The faster the rate of cooling, the smaller the grain sizes. Passivation is another method that involves the formation of an oxidized layer to protect against corrosion.

Candidate:

Stainless steel has several properties that make it useful for orthopedic implants. Low amounts of carbon reduce brittleness, while the addition of molybdenum reduces pitting corrosion. Chromium generates an oxidation layer, providing further protection against corrosion. It is tough with a young man’s high modulus, ductile, tough, and has good fatigue and corrosion resistance. It is also relatively inexpensive.

Candidate:

Yes, there are some disadvantages to using stainless steel in orthopedic implants. It is susceptible to crevice and galvanic corrosion, particularly when used with Co-Cr heads, and it is not self-passivate. It is also prone to causing stress-shielding due to a Young’s modulus mismatching with bone.

Candidate:

Stainless steel is commonly used in orthopedic surgery for plates, screws, intramedullary nails, K-wires, and external fixator pins.

Candidate:

Ti-6Al-4V titanium alloy is composed of 90% titanium, 6% aluminum, and 4% vanadium. It has a biphasic hexagonal-close packed and body-centered cubic structure that provides high fatigue resistance, making it ideal for load-bearing implants such as nails. The manufacturing process is similar to stainless steel and involves casting, hot and cold working, alloying, quenching, and passivation.

Candidate:

The advantages of using Ti-6Al-4V titanium alloy include high fatigue resistance, self-passivation that protects against corrosion, biocompatibility, lower density, and less Young’s modulus mis-match with bone. It is also about 1.6 times tougher than stainless steel, making it a good option for load-bearing implants. The disadvantages include low wear resistance, poor notch sensitivity, potential cytotoxicity of vanadium ions when released, and cold welding with locking screws when there’s a physical disruption of the passivation layer. It is also more expensive due to the difficult fabrication process.

Candidate:

Ti-6Al-4V titanium alloy is commonly used for plates, screws, intramedullary nails, and femoral stems. Additionally, the Tritanium coating from Stryker, a reticulated porous titanium coating, provides higher porosity compared to titanium and cobalt-chrome beads, allowing for excellent bone ingrowth.

Candidate:

The cobalt-based alloy used in orthopedics consists of 60% cobalt, 30% chromium, 5% molybdenum, and trace elements. Its manufacturing process is similar to that of stainless steel and titanium alloy, involving casting, hot and cold working, alloying, quenching, and passivation.

Candidate:

The advantages of using cobalt-based alloy include excellent resistance to crevice corrosion, good biocompatibility with low risk of allergic reaction and immune response, ductility, and excellent wear resistance and toughness. The disadvantage is poor scratch profile forming peaks and troughs, which can lead to implant failure. It is also expensive and can cause stress shielding due to high stiffness and Young’s modulus.

Candidate:

Cobalt-based alloy is commonly used for bearing surfaces such as femoral heads in total hip replacement and the femoral component in total knee replacement. However, it is too stiff to be used for plates and nails due to the problem of stress shielding.

FRCS Case Studies

Curriculum

Stainless Steel , Titanium and Cobalt-Chrom

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