Corrosion of Implant Materials

Any time a foreign material is placed inside the human body, the manner in which that material will affect the body must be considered. There are many causes that contribute to the corrosion of metals when placed inside the human body. After surgery the pH surrounding the implant is reduced to a pH between 5.3-5.6 typically due to the trauma of surgery. Infectious microorganisms and crevices formed between components can reduce oxygen concentration, both of which contribute to the corrosion of the implant.

Materials used must meet the biocompatibility constraints set forth by the Food and Drug Administration (FDA). If a company wants to introduce a material inside the body, the firm must demonstrate, through testing and analysis, the material's biocompatibility. Biocompatibility is the extent to which a material is compatible or friendly with the body. The major materials used for implants today include titanium alloy, cobalt chromium, and stainless steel. All these materials are considered biocompatible by the FDA . However, they all corrode and can cause complications inside the body.

A concern has recently surfaced in the biomedical field about the possible propensity for cobalt-chromium to cause cancer. Cobalt-chromium consists of the elements cobalt, chromium, nickel and molybdenum. There is a concern that the corrosion of cobalt-chrome in the wet, salty surroundings of the human body may be sending toxins streaming into the body, possibly causing cancerous tumors. Even though only about fifteen tumors have ever been reported at the site of an implant, many more could exist and go unreported (partially due to the age of most patients). Although these concerns have met some strong opposition in the industry, many companies are pushing towards safer materials. Such materials include titanium, inert fiber-reinforced composites, and ceramics. Studies involving titanium have illustrated that this material is generally well tolerated in the body.

Some other effects of corrosion exist in the implant materials. Skin conditions such as dermatitis have been reported from exposure to nickel. Cobalt shows signs of causing anemia by inhibiting iron from being absorbed into the blood stream. Ulcers and central nervous system disturbances have been detected as a result of chromium. Aluminum present in some implant materials may cause epileptic effects and Alzheimer's disease. Most of these side effects were the result of testing done outside the body in a different state from the implant. However, they do illustrate the possible hazards associated with the corrosion of implant materials inside the body.

Because all metals corrode, preventing corrosion is difficult. The only apparent solution to this problem rests with reducing the amount of corrosion by choosing better quality materials. Efforts should also be made to use materials whose corrosion does not create adverse effects inside the body, such as titanium. These efforts can reduce the complications associated with corrosion.

The common denominator of these types of complications is that they all increase pain and reduce the functional capacity of the implant. This leads to a subsequent loss in quality of life of the patient. Thus, the complications prevent total hip replacement from achieving its goal.

(The Results of Total Hip Repacement)