In hip and knee replacement surgery, the hip and knee prostheses are made from metal. Metal can be a problem for those with hypersensitivity to metals, especially those with a nickel allergy. There are other materials that may be used in place of nickel to make the joint, but they come with their own set of drawbacks. In this blog post, we will talk about what you should do if you have a metal allergy or sensitivity and need knee replacement surgery.
Contents
What metals are typically in a knee replacement?
There are several metal alloys typically found in knee replacements including cobalt, chromium, titanium, and nickel. These metals combine long-term durability with biocompatibility.
What is a metal allergy?
Metals found in knee prostheses can cause activation of your immune system, leading to implant failure. Metal hypersensitivity (also known as metal allergy) is considered a Type IV hypersensitivity. This is a type of allergy where the presentation of symptoms is delayed (not an immediate reaction as in anaphylaxis or allergic shock).
There are two phases to a type IV hypersensitivity. During the first phase, your body becomes sensitized to the metal. Eventually, the proteins in your body bind to the metal forming antigen-hapten complexes. The antigen-hapten complexes are then presented to T-cells, macrophages, and other immune cells found in your synovial tissue.
These T-cells are then responsible for various symptoms including increased swelling, stiffness, pain, loss of motion, and a rash.
Metal hypersensitivity is a controversial topic, as many orthopedic surgeons do not believe in metal allergies. Many orthopedic surgeons will consider using special implants for patients who notice an allergic contact dermatitis reaction after their skin touches cheap metals.
How common is a metal allergy in the population?
In the general population, it is estimated that the prevalence of a nickel allergy is 13%, cobalt is 2% and chromium is 1%. Allergy to other metals is fairly rare. However, the presence of a skin allergy alone, may not dictate an allergic reaction to a knee replacement. If you notice that you have a skin rash after wearing costume jewelry, you may be allergic to nickel. Please let Dr. Morton know if you have contact dermatitis secondary to a nickel allergy.
How do I know if I have a metal allergy?
Patients who are considering knee replacement are often asked about their history of allergies. If patients note that they have a contact allergy following direct contact to metal exposure, such as with costume jewelry, then they may have a nickel allergy. Tattoo inks have metal salts in them as well, so someone who develops contact dermatitis following getting a tattoo might be at risk of a cobalt or nickel allergy.
Symptoms of a metal allergy can take from 4 weeks to 2 years to develop symptoms after surgery.
Before diagnosing an allergic reaction to metal, other causes of persistent pain should be ruled out such as:
- Infection
- Midflexion instability
- Malalignment
- Patella tracking issues
- Implant loosening
- Metallosis
To rule out these other possibilities you may undergo multiple tests including laboratory tests (such as cobalt and chromium levels), x-rays, bone scan, and biopsy.
The American Contact Dermatology Society has defined criteria for diagnosis of Post Implantation Metal Hypersensitivity Contact Dermatitis in patients with unexplained pain and/or failure of the offending implant:
Major criteria
- Eruption overlying the metal implant
- Positive patch test reaction to a metal used in the implant
- Complete recovery after removal of the offending implant
- Chronic dermatitis beginning weeks to months after metallic implantation
Minor criteria
- Dermatitis reaction is resistant to therapy
- Morphology consistent with dermatitis (erythema, induration, papules, vesicles)
- Systemic allergic dermatitis reaction
- Histology consistent with allergic contact dermatitis
- Positive in vitro test to metals (e.g., lymphocytes transformation test)
What does contact dermatitis after knee replacement look like?
The rash can sometimes be surrounding just the skin incision, the entire body, or sometimes surrounding the entire joint. The rash is typically an allergic contact dermatitis erythematous (red) and papular (small, raised bumps in the skin). It is of variable presentation. The rash typically does not go away with topical treatments for hypersensitivity reactions
What is allergic patch test for allergic contact dermatitis?
Patch testing is commonly used to detect allergic contact dermatitis to metals. It is a test performed by testing your skin with small doses of the irritant. An allergist will then monitor for allergic patch test reactions to confirm if you have a contact allergy to metals. The sensitivity and specificity of this test are only 77% and 71% for determining if a patient has a hypersensitivity to metal. This test can be used to test for nickel allergies, chromium allergy, cobalt allergy, and cement allergy. Furthermore, an allergic reaction at the level of the skin, may not correspond to an allergic reaction at the level of the bone or muscle layer.
As a result, this test is not considered to be reliable for determining if a patient has a metal allergy secondary to their knee replacement.
What is the lab test for a metal allergy following knee replacement?
There are a few tests that have been created. None are widely available.
The most common test that is available is the lymphocyte transformation test. The lymphocyte transformation test is a blood test that compares how many white blood cells are created after 7 days with and without exposure to metal. This test has higher sensitivity compared to patch test alone.
What does the x-ray for a hypersensitivity response for a knee replacement look like?
X-rays in patients with metal hypersensitivity reactions often look normal. Sometimes there is osteolysis (loss of bone) around the metal implants on x-ray. This loss of bone can sometimes lead to severe loosening of the components and failure of the knee replacement.
What do biopsies of metal allergies look like?
Often times during implant removal, intra-operative biopsies are obtained. These biopsies usually demonstrate increased lymphocyte infiltration into the synovial tissue. The synovial tissue is the tissue found within the knee joint that is responsible for the generation of fluid in the knee (synovial fluid). Oftentimes, the synovial tissue will show granulation tissue, fibrosis, numerous giant cells, and calcification. These findings are consistent with a chronic inflammatory response.
What are the treatments for nickel allergy after knee replacement?
Many patients demonstrate improvements following a short-term therapy with topical steroid medication for the rash. Anti-inflammatory medications and physical therapy may treat the symptoms of synovitis (inflamed tissue).
If symptoms do not resolve, revision surgery with a hypoallergenic implant may be considered.
Symptoms should resolve two to three months after revision surgery.
What are the possible alternatives to nickel implants in total knee replacement surgery?
Several manufacturers provide alternative knees for hypersensitive patients. Options include adding a coated layer on cobalt-chromium implants, ceramic-covered implants, and titanium implants. Most of these implants are designed to minimize allergic reactions to nickel.
Coated implants add a layer of coating over the implant to prevent exposure to the underlying metals. Common coating options include Titanium-nitride (TiN), Zirconia Nitride, and Titanium Nobium. Studies of these implants demonstrate that some of these implants have a higher revision rate (sometimes 91% at 5 years). At revision, implant-retrieval studies demonstrate that 20% of these implants have coating delamination and exposure to the deeper layers. This may cause nickel release and lead to a continued immune response.
Ceramic implants include oxidized zirconia (Oxinium). This implant utilizes a femur that is coated with oxinium and a tibia that is made of titanium, thus avoiding nickel allergy issues. Concerns arise from the Australian Joint Registry, where 12-year outcomes demonstrate a 2x higher risk for revision in Oxinium knees. This is similar to the American Joint Registry evaluating 7-year data of these implants.
Titanium implants typically undergo a hardening process that creates a nitrogen-enriched zone on the surface of a titanium femur component. Interestingly, implants that undergo this process demonstrate a 96% reduction in wear rates compared to conventional implants and may lead to longer-lasting implants. This is the implant of choice for Dr. Morton in patients who are concerned of a metal allergy.
Do I need a hypoallergenic knee replacement if I do not have a history of metal allergies?
In patients who do not have an allergy prior to surgery do not necessarily require a hypoallergenic knee replacement. The available tests are unreliable. Furthermore, there may be some concern regarding the longevity and clinical performance of these implants. If you do have an allergic contact dermatitis reaction to nickel, you discuss this with Dr. Morton and you may be a candidate for a hyper allergenic knee replacement.
Should I consider a revision knee replacement if I have a painful knee replacement?
Success rates for revision knee replacement where there is a strong suggestion that there is a metal allergy are variable. There have been several case series published demonstrating successful treatment of metal allergy with revision to a knee replacement without nickel. There are also reports of patients who do not do well with the surgery. Discuss with Dr. Morton if you would be a candidate for revision knee replacement.
Conclusion
If you are considering a total knee replacement and have a metal allergy or sensitivity, speak with Dr. Morton about the possible alternatives. There are several manufacturers who provide alternative knees for patients who are allergic to nickel, but they come with their own set of drawbacks. If you had a knee replacement and believe that you may have a hypersensitivity reaction, schedule an appointment with Dr. Morton today.
