Historical Perspective of Metallic Implants

The first metal alloy developed specifically for human use was "vanadium steel" in the early 1900's.The earliest successful implants were bone plates, introduced in the early 1900s to stabilize bone fractures and accelerate their healing. As early as the first bone plate implants, surgeons identified material and design problems that resulted in premature loss of implant function, as evidenced by mechanical failure, corrosion, and poor biocompatibility. Design, material selection, and biocompatibility remain the three critical issues in today's biomedical implants and devices.

In 1920 attempts to employ surgical implants were still hampered by the limitation of available materials. In 1924 Zierald published the study on the reaction of tissues to a variety of metals. Iron and steel, the most widely employed materials at the time, were noted to dissolve rapidly and to provoke erosion of adjacent bone. Substantial discoloration of tissues was observed around specimens of copper, nickel, embedded in bones. A problem existed, as the metals which did not produce discoloration, e.g. gold, silver, or pure aluminum, were all too soft or weak for most applications.

In 1926 18% chromium, 8% nickel stainless steel was introduced into surgical applications. This material was noted to be much more corrosion resistant in body fluids. This was stronger and more resistant to corrosion than the vanadium steel initially introduced by Sherman for his fracture fixation plates. Later in 1926, 18-8SMo stainless steel, which contained a small percentage of molybdenum, to improve the corrosion resistance in salt water, was introduced. This alloy became known as 316 stainless steel.

The next alloy to be introduced into orthopedic practice was titanium and its alloys. In 1947 possible applications for titanium surgical implants were considered. The pure metal had shown excellent inertness in an environment of seawater, so that corrosion resistance seemed likely to be good in the human environment. A few surgical implants were made and inserted into human subjects. Upon their removal, excellent corrosion resistance was confirmed. Subsequently, Maurice Down introduced a variety of titanium orthopedic fracture devices such as plates and screws.

In the 1950's the carbon content of 316 stainless steel was reduced from 0.08% to 0.03% for better corrosion resistance and became known as 316L stainless steel.

(Metals in Orthopaedic Surgery)