Updated January 01, 2014.

Question: Should You Worry about Metal Ions after Metal-on-Metal Hip Replacement?

Answer:

The short answer is no. Studies so far seem to indicate metal-on-metal hip replacements are safe. The longer answer is that this is an emerging area of surgery. Alternatives to traditional metal and plastic joint replacements are being investigated in an effort to improve the results of joint replacement surgery.

In particular, several newer types of implants have been investigated in the setting of hip replacement surgery.

These alternatives to metal and plastic hip replacements include:

• • Metal-on-Metal
  • Ceramic-on-Plastic
  • Ceramic-on-Ceramic

The goal of these alternative types of hip replacement are to:

• Increase the longevity of the implant
  All implants slowly wear out over time. The implants become thinner, much like the tread on your car tire slowly wears out over time. The metal and ceramic implants wear much more slowly than the plastic implants. Because they wear out more slowly, it is hoped that the implants will last longer, although this has not been proven.
• Increase the stability of the implant
  The larger the implant, the more stable the implant will be. One of the major complications of hip replacement surgery is the concern of possible dislocation of the replacement. Larger implants have less chance of dislocation. However, when metal-and-plastic is used, the larger implants can lead to accelerated wearing out of the joint replacement. Metal and ceramic implants can be used in larger sizes, with less risk of wearing out quickly. Therefore, by using a larger implant, the joint is more stable. This means less of a risk of dislocation.

Metal Ions

One of the downsides of these metal-on-metal implants is the concern that the body will accumulate metal ions. All implants will slowly wear out over time. The metal-on-metal implants wear much less than metal and plastic implants, but the wearing out that does occur with metal-on-metal implants causes the release of metal ions into the body. These metal ions can be detected in blood and urine samples, and the levels tend to increase as time passes.
Do the metal ions cause problems in the body?
When it was first determined that these metal ions slowly accumulated in the body, people were concerned about higher rates of cancer, and allergy-like reactions to the metal.

There have been no studies to show a higher risk of cancer, hypersensitivity, or other adverse effects of these metal ions. This is good news, but it is certainly not the final word. Long-term studies looking into the effects of these metal ions over the course of decades are in progress, but the final results are unknown.

_Sources:

• Dumbleton JH, Manley MT; "Metal-on-Metal total hip replacement: what does the literature say?" J Arthroplasty. 2005 Feb;20(2):174-88. Review.