Problems With Metal-on-Metal Hip Replacements

Metal on metal hip replacements have the advantage of durability, but they may also have adverse effects, such as the potential for inducing an inflammatory reaction.

Hip replacement surgery is a treatment option that's considered when advanced hip arthritis leads to severe joint degeneration. Your healthcare provider may discuss this surgery with you if your hip arthritis is interfering with your normal activities and has not improved with non-surgical treatments.

When you are considering hip replacement surgery, you probably want your implant to last a long time—hopefully, for the rest of your life. Over the past several decades, new hip replacement implants have come and gone. While implants have improved, they still wear out, so there is a great deal of interest in new designs that may lead to a better, longer-lasting hip replacement implant.

Hip Replacement Implants

A hip joint is replaced with an artificially designed prosthetic implant. Implant designs date back to the 1960s, but have evolved over time. Some implant designs have been used for decades, with long track records—others are brand new and have no track record.

Newer products have some advantages because they are often designed to avoid problems that are noted with existing implants. However, an advantage of using an implant that has been around for a while is that more is known about long-term results with the implant.

Metal-on-Metal Hip Replacements

Metal-on-metal hip replacements have been done for many years. Metal-on-metal implants are also used for hip resurfacing implants.

Metal-on-metal implants use a similar design to standard hip replacements, but the surfaces of both the ball and the socket are made of metal. These metal surfaces are highly polished and smooth. In addition, the surfaces are much harder than the traditional artificial plastic hip socket, making it less susceptible to wearing out.

Advantages

Metal-on-metal hip replacements have two advantages.

Size and stability: First, the size of the ball of the metal ball-and-socket implant can be larger than it could be if it's made from some other materials. This larger metal ball is more stable and less prone to hip dislocation. This is an advantage if you are physically active. In a traditional metal-and-plastic hip replacement, the socket is made of plastic that takes up space. With metal-on-metal implants, there is no plastic taking up space, and the metal ball can be larger.

Durability: All materials used for joint replacements wear out over time, some faster than others. The plastic in the standard metal-and-plastic hip implants is known to wear out over time. New materials that don't wear out as easily include new plastics, ceramics, and metal.

Problems

Patients with these metal-on-metal implants have been found to have high levels of metal ions in their bloodstream, evidence of microscopic particles from the implant escaping into the body. The effect of these metal ions in the bloodstream is not fully understood, although there is no evidence of problems in other parts of the body, just the effects on the hip itself.

The concern about some metal-on-metal hip replacements, specifically one implant made by a Johnson & Johnson Company called DePuy Orthopaedics, is that implants were causing problems within the first few years after replacement. While the materials don't wear out quickly, they do create microscopic particles of metallic debris. The body seems to react to this microscopic debris with an immune response. This can lead to soft-tissue and bone damage around the hip joint. In some patients, this tissue damage has been severe causing permanent injury and requiring additional surgery. Patients with this particular implant are much more likely to need their hip replacement repeated.

What You Should Do Now

If you have this specific type of metal-on-metal hip replacement implant, you should see your healthcare provider for routine evaluation of your hip joint. There are specific surveillance tests recommended for patients with this implant—and further surgery might be considered if there's a problem.

Patients with other types of metal-on-metal hip replacement implants should also be seen regularly by their surgeon for continued evaluation. Only a limited number of metal-on-metal implants have been recalled, and even those recalled implants may not need to be removed. However, because of these concerns, these implants should be closely monitored to watch for potential problems.

Why Did This Happen?

How can it happen that tens of thousands of patients received an implant that was ultimately determined to be a failure? This is an excellent question, and this issue is shining a bright light on the process by which medical devices are reviewed and approved for implantation.

Surgeons need to be mindful of companies touting a new system that may lack clinical data. Patients need to be educated about the potential risks of different types of implants. It is important to understand that all implant types are imperfect, and determining which is best can be a challenge for healthcare providers and patients.