Are you considering knee, hip, or other joint replacement surgery for osteoarthritis (OA)? 

More than a million hip and knee joints are replaced each year, most of them due to OA. These procedures are generally safe and effective for the right candidates. Yet, there have been increasing media reports of people having allergic reactions to the metals used in joint implants.

Despite the media attention these adverse reactions can draw, metal implant allergies are uncommon, says Joshua J. Jacobs, MD, professor and chair of the department of orthopaedics at Rush University and president of the American Academy of Orthopaedic Surgeons. Dr. Jacobs discussed the issues related to metal sensitivity to joint implants at the 2012 annual meeting of the Association of Bone & Joint Surgeons.  “I think metal implant allergy is a real entity, but it happens very rarely,” he says.

Doctors are becoming increasingly aware of the possibility that their patients may have a reaction to an implanted joint. Still, they are cautious about giving allergy tests across the board to people without known metal allergies, because none of the available tests has been well studied, Dr. Jacobs adds.

Metal Joints and Allergies

Prosthetic parts used to replace a damaged knee, hip, or shoulder joint in the U.S. are made from—or contain metal, because of its durability and the fact that it can stay intact inside the body without corroding. Chromium, nickel, cobalt, titanium and molybdenum are among the most common metals found in implants. Often, a prosthetic joint will contain more than one of these metal types.
 
A small number of Americans are allergic to one or more metals:

  • Nickel allergy is the most common metal sensitivity. 
  • Up to 17% of women and 3% of men have a nickel allergy. 
  • About 1% to 3% of people are allergic to cobalt and chromium.

What’s less clear is how often allergic reactions cause problems for people with metal joint implants. Studies have shown that in some people with a metal allergy, the metal in the implant triggers an immune reaction when it comes into contact with body fluids. When the circulating blood containing traces of the metal reaches the skin, it causes a skin rash, called dermatitis. The worst of the irritation is typically centered around the implant site.

Symptoms of a skin (cutaneous) reaction can include:

  • Rash
  • Hives
  • Blisters
  • Swelling of the skin tissue

The reaction also can occur deeper inside body tissues. This is called a systemic reaction. It’s a delayed response to the metal caused by specialized immune cells called T cells. The mechanism is similar to that in a skin response, but in the skin, the reaction is caused by a different type of immune cell, called a Langerhans cell.

The evidence about body-wide symptoms has been mainly anecdotal. There have been reports of a Georgia woman who had systemic symptoms due to a metal contact allergy after knee replacement surgery, as well as of an artist who developed body-wide symptoms after a double knee replacement and a Denver woman who reacted to a metal hip implant.  

Symptoms of a body-wide (systemic) reaction that have been reported in these types of cases include:

  • Pain in the joint implant area and in other parts of the body
  • Weakness
  • Fatigue
  • Loss of joint function
  • Diarrhea
  • Headaches

Doctors say the body-wide type of reaction is rare and hasn't been well documented in other people who have had joint replacements, primarily because it’s hard to distinguish between an allergic reaction and complications of the surgery itself. “Sometimes it can be difficult to sort out differences between an allergy to the implant and an infection,” says Ariel Teitel, MD, a rheumatologist and clinical associate professor of medicine at NYU Langone Medical Center.

Should You Be Tested Before Implant Surgery?
If you are going to have joint replacement surgery, ask your doctor if you should have an allergy test. Because metal allergies are relatively rare, testing before joint replacement surgery isn’t recommended for everyone, says Dr. Jacobs. However, if you’ve had a skin reaction to metal jewelry in the past, you probably should be tested.