Metal Allergy and Knee Implants

Why Are Allergies on the Rise?

One major reason, for allergies to be on the rise, seems to be our changing environment. While genetics play a role, the rapid increase in allergies and autoimmune diseases points more strongly to outside factors like pollution, industrial chemicals, and even what we’re exposed to in our homes and workplaces.

For example, heavy metals — such as cobalt (Co), chromium (Cr), copper (Cu), and lead (Pb) — are found in many everyday sources. From traffic pollution and cigarette smoke to certain fertilizers and even the water we drink, we’re often exposed without realising it. These metals can enter the body through breathing, eating, or even skin contact.⁷

What Does This Have to Do With Implants?

Many medical devices, including dental fillings, contraceptive devices, pacemakers, and joint implants like artificial knees and hips, may contain trace amounts of these metals. Most people tolerate these implants very well. But for some individuals, especially those with an overactive immune system or existing allergies, these metals can trigger what’s known as Delayed-Type Metal Hypersensitivity reaction.

This kind of reaction doesn’t always happen right away, and symptoms can sometimes be vague things like ongoing inflammation, skin rashes, joint pain, or swelling. If you already know you have sensitivities to metals like nickel or cobalt, or if you’ve had trouble with reactions to jewellery or suffer from eczema, asthma or Hay-fever, it’s important to tell your doctor before any surgery or implant procedure.⁵

For a small number of patients, the body can react to tiny metal ions that may wear off from the implant over time. These metal ions can be released into your surrounding tissue, especially if the implant experiences damage or unusual stress (it is called metallosis).

What You Should Know About Metal Wear in Knee Implants

Even though many hip replacements now use ceramic materials, most knee implants still rely on a strong metal alloy made of cobalt, chromium, and molybdenum (CoCrMo).

This metal helps the implant last through everyday activities like walking and bending—but like any material, it can wear down over time.

Researchers are learning that some wear and tear on these metal knee components may release tiny metal ions into the surrounding tissue. In most cases, this doesn’t cause any noticeable problems. However, in some people, it may lead to local reactions like inflammation or, more rarely, even a reaction from the immune system. These reactions are similar to what was seen in hip implants and can sometimes result in pain, swelling, or the need for further surgery.

A recent study looked at 51 knee implants that had been removed during revision surgery.⁶ Of these, the researchers found that the patients with the implants that had more visible wear had higher levels of cobalt, chromium, and molybdenum levels in their surrounding joint tissue. This means that as the metal wears, more of it is absorbed into your body.

They also found that metal debris can be released in different ways—during surgery, when the metal parts are first put in, and later through regular use of the joint. Even small contact between parts, or tiny particles caught between them, can cause extra wear.

This doesn’t mean metal implants are unsafe. In fact, they’re used successfully in thousands of surgeries every year. But for certain patients — especially those who are sensitive to metals or have a history of allergies — it’s something you should discuss with your surgeon and take steps to reduce your risk of this complication.

When your immune system reacts to these metals (commonly nickel, cobalt, and chromium), you might experience symptoms such as:²

• Persistent pain around your knee
• Swelling and inflammation
• Stiffness and reduced range of motion
• Skin reactions like dermatitis or eczema in the area
• In some cases, implant failure requiring revision surgery