In the 1990s, there was growing concern with the experience many patients were having with traditional metal-on-polyethylene bearings, which were the most common bearings used at the time. The polyethylene liners available at that time were wearing out, breaking, dislocating and causing other complications for patients, such as bone loss, from polyethylene wear particles. For example, the Swedish National Hip Arthroplasty Register 2000 Annual Report reported that metal-on-polyethylene bearing surfaces in males under 55 were showing revision rates as high as 20% at ten years after the date of implantation.1
At the same time, younger, heavier and more active patients were seeking hip replacement surgery. There was a clear need for a better hip implant – one that would not just have improved performance in the existing population of patients, but which could also stand up to the stresses of these younger and more active patients. This spurred the orthopaedic industry and surgeons to seek different bearing options that reduced wear and improved stability.
Given the advancements in manufacturing, materials and overall device technology, the general consensus in the orthopaedic and scientific communities was that metal-on-metal bearings were an appropriate option to pursue in seeking an improved hip implant option that would address the issues seen with metal-on-polyethylene at the time. Surgeons, scientists, engineers and academics drew on years of experience in developing a new generation of metal-on-metal bearings. In the 2000s, various orthopaedic device manufacturers developed and marketed dozens of metal-on-metal bearing options.
DePuy knows and understands that some metal-on-metal bearing options – including the ASRTM Hip System that the company recalled in 2010 – have not performed as expected for some patients. Not all metal-on-metal products are the same and each should be evaluated on its own merits. ULTAMET® Metal-on-Metal Articulation is backed by a strong record of clinical data showing reduced pain and restored mobility for patients suffering from chronic hip pain.
As advancements in bearing technology have continued and physician preferences have shifted toward metal-on-polyethylene, ceramic-on-polyethylene and ceramic-on-ceramic bearings, demand for metal-on-metal bearings has declined. In the United States and Europe in 2012, metal-on-metal bearings comprised less than two percent of the bearings implanted.2
Surgeons choose from among a variety of bearing material options when selecting a hip implant for a patient, and they make that decision based on a variety of factors, including the patient's age, weight, and activity level.
When most any surface rubs against another, there are changes happening at a microscopic level, including tiny particles wearing away. The same is true with hip implants. No matter what materials are used, hip implants experience wear over time and generate what are called wear particles that are released into the area surrounding the hip.
"All artificial hips require one component to slide against another component and it is inevitable that material at the surfaces will wear as they interact."8 (U.S. Food and Drug Administration)
Researchers have studied wear particles for many years. What they have found is that the components of metal-on-metal hip bearings generate a lower volume of wear particles than either metal-on-polyethylene or ceramic-on-polyethylene bearings.3
“At the current time, the FDA believes there is not enough evidence in the U.S. demonstrating a correlation between a metal ion level and the presence of localized lesions, clinical outcomes and/or the need for revision surgery.”9 (U.S. Food and Drug Administration)
For most patients, these wear particles do not cause problems.4 The body's natural defenses respond to the particles by isolating or eliminating them from the body. For some, the wear particles might cause a reaction that results in symptoms in the area surrounding the hip joint, such as fluid or tissue buildup.5 Further surgery can be required, and this is true for all types of hip implants regardless of the materials from which they are made. Across all of the research, scientists have not found any reliable evidence that these wear particles cause harm in tissues or organs in areas of the body other than the hip.6
According to the U.S. Food and Drug Administration, it is not possible to predict who will experience a reaction to wear particles, what type of reaction they may have, when the reaction may occur or how severe the reaction will be.7
Wear from metal-on-metal bearings can also result in the release of ions. The ions come from the base elements that the hip component is made of, such as chromium and cobalt. Chromium and cobalt are naturally occurring elements that the body needs. In fact, cobalt and chromium can be found in foods and vitamin supplements. Cobalt is important for our metabolism and found in fish, cereals, nuts, green leafy vegetables, chocolate and dairy products. The level of these ions in the body can be measured through medical tests. However, there is no definitive data connecting the level of the ions and any health-related problems.
For more information on Metal-on-Metal hip systems, please click here.
- Swedish National Hip Arthroplasty Register 2000 Annual Report
- Based on multiple sources including Orthopedic Network News, industry surveys and internal company estimates
- Anissian, H., et al. “Metal-on-metal bearing in hip prosthesis generates 100-fold less wear debris than metal-on-polyethylene.” Acta Orthopaedica Scandinavica 70 (6), 1999: 578-82.