Metal Allergy Knee Replacements 

Understanding Metal Hypersensitivity and Modern Implant Options

Total knee replacement is a highly successful operation that restores mobility and relieves pain in patients with advanced arthritis. For a small number of people, however, metal sensitivity or allergy may be a consideration when choosing the most appropriate implant.

What is Metal Hypersensitivity?

Metal hypersensitivity is an immune reaction to certain metals commonly used in medical implants, such as nickel, cobalt, and chromium. These metals are widely used in orthopaedic implants because of their strength and durability.

Studies suggest that 10–15% of the general population has some form of metal sensitivity, most commonly to nickel.  

Among patients undergoing knee replacement, approximately 14–16% report a history of metal allergy, although true implant-related reactions remain relatively uncommon.  

In rare cases, hypersensitivity may contribute to symptoms such as:

• Persistent knee pain after surgery
• Swelling or stiffness
• Skin reactions or eczema
• Inflammation around the implant
• Implant loosening in severe cases

The biological mechanism is typically a delayed immune response (Type IV hypersensitivity) triggered by microscopic metal ions released from implant surfaces over time.  

Genetic and Individual Risk Factors

Not all patients with metal allergy develop problems after knee replacement. However, certain individuals may have a higher risk, including:

• Patients with known nickel or jewellery allergies
• Those with a strong personal or family history of allergic reactions
• Individuals with autoimmune or hypersensitivity disorders

When there is a history suggestive of metal sensitivity, testing such as patch testing or lymphocyte transformation testing (LTT) may help guide implant selection.

Modern Solutions: Hypoallergenic Knee Implants

Advances in implant technology have led to the development of hypoallergenic knee replacements, designed to reduce metal ion release and improve biocompatibility.

One example is the knee systems developed by B. Braun through its orthopaedic

Advanced Surface Technology

Some B. Braun knee implants use Advanced Surface (AS) technology, which incorporates a specialised seven-layer ceramic coating over the metal implant.

This technology offers several advantages:

• Zirconium nitride ceramic surface that is highly biocompatible
• Effective barrier against metal ion release
• Improved scratch and wear resistance
• Up to 65% reduction in wear compared with standard implants  
• Reduced inflammatory response and improved biological compatibility  

The multilayer coating acts as a protective shield between the metal alloy and the surrounding tissue, helping minimise potential allergic reactions in susceptible patients.

 Clinical Outcomes

Clinical studies of coated knee implants demonstrate excellent long-term outcomes and durability. In one randomized study, coated knee implants showed 98% implant survival at 10 years, with high patient satisfaction and good functional outcomes.  

 These results indicate that modern coated implants can provide reliable performance while reducing the risk of metal-related reactions. 

A Personalised Approach

Metal hypersensitivity is uncommon but increasingly recognised in joint replacement surgery. For patients with known allergies or concerns about implant materials, modern implant technology allows surgeons to select implants designed to optimise biocompatibility, durability, and long-term success.

If you have a history of metal allergy, it is important to discuss this with us at the appointment so the most appropriate implant can be selected for your individual needs.