Could You Be Allergic to a Joint Implant?
Here's what you need to know before joint replacement surgery.
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:
- 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
- Loss of joint function
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.
“You may be able to identify which metal a patient is allergic to, which can potentially dictate which metal to choose for the implant,” explains Dr. Jacobs. For example, if you are allergic to nickel, your doctor may suggest an implant made from chromium or titanium. If you are allergic to multiple metals, talk to your doctor about an implant made from a titanium or zirconium alloy. These substances are less likely to cause an allergic reaction.
The most commonly used test to diagnose a metal allergy is skin patch testing. Very small amounts of various metals are placed on your skin and then covered with a patch. After a couple of days, you return to the doctor and the patches are removed. If the area under one or more of the patches is irritated, you are likely allergic to that metal.
Tests for Metal Allergies
Skin patch testing is not 100% accurate, though. It is possible to have a false negative or false positive result. This means the test finds that you don’t have an allergy when you actually do, or vice versa. More research is still needed to determine how well patch tests can diagnose allergies to metal joint implants.
Researchers at National Jewish Health in Denver say they've developed a new blood test that can more accurately diagnose nickel allergies before implant surgery. “The test can see if the person’s white blood cells … react to the nickel,” says Karin Pacheco, MD, associate professor in the Division of Environmental and Occupational Health Sciences, who developed the blood test. This test has been validated against the skin patch test, and Dr. Pacheco says it works equally as well, but there is also limited research to confirm its effectiveness.
The blood test can also detect the degree to which the immune system is stimulated. “That can be helpful in terms of trying to grade the response,” Dr. Jacobs says. And, because the blood test involves only a simple blood draw, it can potentially be done in centers that don’t have the ability to do patch testing. As of March 2014, the nickel allergy blood test is currently only available at National Jewish Health. However, doctors elsewhere in the country can send a patient’s blood sample to the center to be tested. Results are returned in a little over a week.
Another available metal allergy test is called MELISA (memory lymphocyte immunostimulation assay). Like Dr. Pacheco’s test, it looks for a white blood cell reaction against the possible metal allergens. But the MELISA test has not been validated against patch testing.
There are still many uncertainties surrounding metal implant allergies, and the tests used to predict them. For now, detecting a metal allergy is an imperfect science, but the technology is improving. “Hopefully, as we define the role of allergy testing, we can provide some sort of pre-operative test that would be of great value to patients, but I don’t think we’re there yet,” Dr. Jacobs adds.