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Metal-on-Metal Implants Experience (More) Backlash

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Published: March 5, 2010

Metal-on-metal hip implants are no stranger to bad press. Over the years, they have garnered attention for the debris they generate, which can damage soft tissue and bone around the implant. On the other hand, they have remained viable because of the exceptional mechanical strength that they offer, which is critical for such a load-bearing application. A resurgence in metal-on-metal skepticism has returned, however, according to a recent article in the New York Times.

Employed in close to one-third of U.S. hip replacements, metal-on-metal implants can produce sizable amounts of metallic debris as a result of friction between the components of the ball-and-socket configuration. Released into the body, these metallic ions, which generally end up near the implant, stimulate an immune response from the body. Consequently, damage to surrounding bone, called osteolysis, can occur. In addition to inflammation in the area, this condition can cause loosening of the implant and, in turn, the need for revision surgery.

Because of these issues, medical professionals are distancing themselves from metal-on-metal designs, according to the article. The Times cites a recent editorial in the Journal of Arthroplasty that discouraged the use of the implants as well as the 80% reduction of metal-on-metal implant use by the Mayo Clinic in the past year as evidence of this trend.

While the issue is not new, there seems to be a renewed aversion and criticism of metal-on-metal implants. While this situation should be analyzed by device designers, metal-on-metal implants are not the only material with problems; they all have their drawbacks. Polyethylene has also been known to generate quite a bit of debris and cause osteolysis as well. And who can forget the squeaking ceramic hips a few years ago? Despite ceramics’ wear resistance, they also are more vulnerable to fracture than some other materials.

What do you think, readers? Will this backlash have repercussions in the device industry, or will it quiet down as it has before? What needs to be done? Sound off in the comments section and share your thoughts.

Stay tuned for more information on materials for hip implant design in a related special feature in the April issue of MPMN. Plus, read about the companies behind the implants in our Regional Focus on Warsaw, Indiana, which is considered the orthopedics capital of the world.

Comments

So, let’s see. I can have a hip replacement that squeaks, or a hip replacement that causes immune system reaction, degradation of the bone and needs to be replaced in a few years.

Let me think, I know there’s a right answer…

of course, if the New York Times says it’s bad, I won’t do it.

 

Perhaps hip replacement designers should look at mechanical designs that do not attempt to mimic a natural hip joint. You shall never eliminate wear of replacement materials. So, the solution will be with how to capture nano particles created by friction between joint materials rather than have them enter tissues outside of the joint where they may create another medical problem.
info@agscan.net

 

The hip implants have been one of the more successful total joint replacement procedures to relieve pain. Further material research needs to be untertaken in new materials with less wear. A better solution would be to catch any joint deteriation in an earlier stage before significant cartilage damage or bone osteophytes form. Then cartilage regeneration techniques, such as (autologous adult stem cell injection methods or even newer approaches) can be used (once they are develeped of course). Then as the cartilage wears away the technique can be repeated as needed. Major tendon or ligament tears could still be repaired manually but smaller tears may also benefit from regeneration techniques.

 

I believe there is significant potential for the use of better bearing materials than those currently in use. Based on recent patent applications this has been recognized by at least one researcher. I am surprised the industry hasn’t made more rapid advancements in this area in spite of the biocompatibility challenges.

 

A routine design problem for my senior undergrad students is to design an encapsulated, metal-to-metal hip joint, with silicone fluid that can be periodically replaced through sterile needle, ball sealed, Zerc fittings,,,Buddy

 

There are polymer composites that should provide a reliable hip replacement, and it is obvious that the metal-to-metal is a very poor choice. The use of ultra-high-molecular-weight-polyethylene (UHMWP( was a good choice, but it apparently has shown failures. Many years ago, we were involved in research on non-lubricated bearings. The inclusion of selected fillers in a Teflon polymer reduced the wear rate of sleeve bearings by a factor of 1000! It can be anticipated the an appropriate filler or short fiber reinforcement in UHMWP or another polymer will provide a high performance and reliable hip replacement.

 

Why not use a polymer and metal combination bearings have been made from different plastic materials which in some cases out last metal bearings.

 

Well, some years ago there was the polyurethane compliant bearing developed by Pfizer Howmedica (UK) that was amazing – low friction, excellent wear resistance, etc. The technology was shelved after Howmedica sold the technology (to Stryker I believe). If anyone knows anything about why this technology never made it to market I would love to know!

 

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