Hip Replacement and Alternative Bearing Surfaces

If you need a hip replacement, you and your doctor may be discussing what kind of hip implant is the best choice for you. That decision will depend on factors such as your age, general health, quality of your bone, and your level of activity. The information on this page is meant to help you understand alternative bearing surfaces used in total hip replacement, and improvements made to materials used in total hip replacement implants today.

Review this information with your doctor. Joint replacement surgery is usually a last option after all treatments with medication have been exhausted.

Your surgeon can help you determine if Longevity® Highly Crosslinked Polyethylene is the best choice for your hip implant based on:

  • Wear resistance of an alternative bearing surface
  • Multiple options for surgeons, meeting different patient needs

Hip Implants Available Today

The success of total hip replacement depends in part on the materials, design and processing of the
materials used in the implant. During surgery, the painful parts of the damaged hip are replaced with artificial hip parts, which make up a prosthesis—a device that substitutes or supplements a joint. To duplicate the action of a ball-and-socket hip joint, a prosthesis has three parts:

  • The stem, usually made from metal
  • The ball or head, made of ceramic or metal
  • The shell and accompanying liner, with the shell made of metal and the liner made of a plastic called polyethylene. This liner may also be made of ceramic or metal.

Materials for implants in hip replacements have been available for more than 20 years and include:

  • Ceramic-on-Polyethylene (referring to a ceramic head rotating on a polyethylene liner)
  • Metal-on-Polyethylene
  • Ceramic-on-Ceramic
  • Metal-on-Metal

What Factors Can Limit a Hip Implant’s Service Life?

There are many considerations facing patients and surgeons when choosing implants for hip replacement. Eventually, bearing surfaces may wear out and need replacement. Wear is defined as the progressive shedding of minute amounts of material from the implant due to friction or rubbing. Alternative bearings are considered highly wear-resistant and are an “alternative” to conventional polyethylene, which have traditionally had higher wear rates. Today’s bearing surfaces are the result of ongoing research to develop materials that resist wear better and last longer.

Extending Hip Implant Life is the Goal

Improvements are continually being made in materials used for hip implants. For instance:

  • Polyethylene durability has been improved through “crosslinking”
  • Highly crosslinked polyethylene, an advancement in this material, is highly wear-resistant
  • Today's ceramic implants generally resist chipping and breaking better than the early versions.
  • Second generation metal-on-metal products are designed to address loosening that sometimes occurred in first generation metal-on-metal implants

Clinical studies have shown that, generally, the higher the level of crosslinking, the greater the improvement in wear resistance. Zimmer’s highly crosslinked polyethylene is produced using harmless high-dose electron beam radiation, which further links together the molecular structure of the polyethylene. Laboratory testing has shown that in crosslinking, a new three-dimensional structure is created that results in a polymer more resistant to wear.

As stated previously, wear is a key limiter in the service life of an implant. Laboratory studies have shown that the following materials are substantially equivalent in their ability to resist wear:

  • Metal or Ceramic-on-Longevity Highly Crosslinked Polyethylene
  • Metal-on-Metal
  • Ceramic-on-Ceramic

Flexibility for Surgeons is Important

Some key differences in hip implants are in the ability to provide options for surgeons. Choices in liners, neck length, head size and the positioning of the implant components are vital in meeting different patient needs. Neck length is important to restore proper leg length in patients, while head size options help to increase hip motion. It is critical to allow as much flexibility as possible to surgeons when making implant decisions in the operating room and Longevity Highly Crosslinked Polyethylene provides these important liner options.

“Providing options to surgeons when they are choosing implant liner designs, head sizes or neck lengths is important for patients in terms of optimizing overall joint stability.”

—Dr. William J. Maloney, Professor of Orthopaedic Surgery and Chief of Orthopaedic Surgery Services, Barnes Jewish Hospital and Washington University School of Medicine, St. Louis

Download the Understanding Alternative Bearing Surfaces in Total Hip Replacement Brochure (PDF, 131 KB)

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