Sensitivity to the Metal Parts in a Knee Replacement

Can an Allergic Response Be the Source of Pain After Knee Replacement?

Physical therapist helping man with knee trouble
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Knee replacement surgery is a very successful surgery; the vast majority of people who undergo this treatment for severe knee arthritis are satisfied with the surgery. However, not everyone loves their new knee. In fact, about 10-15 percent of people who undergo knee replacement are not happy with their results

Trying to determine why a knee replacement is painful can be a challenging problem for patients and doctors.

Sometimes the problem is clear, such as an infection or a worn out knee replacement implant. However, other times, everything checks out fine. Your doctor tells you there is nothing wrong, but your knee still hurts. What could be causing the pain? Could a reaction to the metal in the artificial implant in your body be the source of the problem?

Metal Sensitivity

Any metal that comes into contact with the body, either through the skin or embedded within the body, causes some degree of metal corrosion. This corrosion leads to the formation of metal ions that can react with proteins in your body; these can be experienced in your body as allergens and can elicit an immune response.

The most common metal ions found in knee replacement implants that can cause hypersensitivity include nickel, cobalt, and chromium. These metals are known to cause skin sensitivity in the general public; about 15 percent of people have nickel sensitivity.

The question has come up if a similar reaction due to metal hypersensitivity can occur within the body that leads to pain and stiffness after joint replacement

This has been a difficult question to answer. Most people, even those with known hypersensitivity skin reactions to metal, don't have a hypersensitivity to a joint replacement implant.

Similarly, many people who are suspected as having a hypersensitivity response to a joint replacement do not have skin reactions to these metals. For this reason, skin testing has not been shown to be useful to either prevent or diagnose a metal hypersensitivity to a metal joint replacement.

Hypersensitivity Reactions

There are two reactions that seem to occur in patients who have metal hypersensitivity to a knee replacement implant. The first is a skin reaction called dermatitis. In this condition a skin rash that looks like eczema can occur. This is typically located over the front of the knee, although in some people can become more widespread. Dermatitis is most often managed with the help of a dermatologist, and fortunately is usually well controlled with topical steroid creams. 

The other reaction that can occur is called synovitis. The synovium is the lining of the knee joint, and a condition that causes inflammation of this tissue is called synovitis. Synovitis can occur with infections of the knee, traumatic injuries to the joint, or when there is a hypersensitivity response.

The challenge is there are several conditions that can cause synovitis of the knee joint, but no test to confirm metal hypersensitivity as a cause. Therefore, this is considered a diagnosis of exclusion, meaning every other cause should be eliminated, and only then should metal hypersensitivity be suspected.

Treatment Options

The challenge with metal hypersensitivity is that typically the diagnosis is unclear (there is no test for the condition) and most often the symptoms are annoying, but not disabling. On top of that, the only possible way to correct the problem, if metal hypersensitivity is the actual cause, is to remove the implant and replace the knee with a special implant made of ceramic or titanium. Therefore anytime metal hypersensitivity is suspected as the source for knee pain or stiffness after replacement, you should proceed with great caution. Even academic and up-to-date surgeons are just learning about this condition, and the optimal treatment is not clear. Performing additional surgery may or may not be helpful. That said, people struggling with pain after replacement may want to consider if this could be a source of pain.


Lachiewicz PF1, Watters TS, Jacobs JJ. "Metal Hypersensitivity and Total Knee Arthroplasty" J Am Acad Orthop Surg. 2016 Feb;24(2):106-12.

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