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Hip Replacement: Learning About Bearing Surfaces
Options in hip replacement include a wide range of sizes, designs, and materials to choose from, allowing your surgeon to fit you with the hip that is right for you.
One of the components your surgeon will select to reconstruct your hip is a metal "acetabular" cup to replace your natural socket, which is called the acetabulum. The acetabular cup is the part of a hip implant that forms the socket in the ball-and-socket structure of the hip joint.
The femoral head at the top of the thigh bone (femur) rotates within the curved surface of the acetabulum.
In a hip replacement procedure, the acetabular cup, usually comprising a metal shell and a liner, replaces the acetabulum or socket. It also includes a femoral head (ball) that allows the hip joint to rotate. The femoral head (or ball), replaces the natural head of the femur (thigh bone) and attaches to the stem.
One important decision your surgeon will make is which "bearing surface" will be used. The "bearing" is the area where the two moving parts of your new hip implant join together and create a movable joint.
You and your doctor may choose to use one of three bearing materials—polyethylene (plastic), metal, or ceramic. No one material or combination is best for all patients and medical conditions. Each of the materials has distinct advantages and disadvantages. Your surgeon will discuss these options with you and choose the materials that best suit your needs, based on many variables which include your age, lifestyle, and weight.
Most doctors use more than one type of bearing in their practice and choose a bearing based on durability, level of performance, wear resistance, and your personal needs. As you become familiar with these options, remember that the bearing itself is not just a single part, but the point where the ball and liner meet; so the bearing can be the joining of different combinations of materials.
Cross-Linked Polyethylene
Metal
Ceramic
Cross-Linked Polyethylene
The bearing component most commonly used for total hip replacement in the United States is a metal femoral head (ball) made of either stainless steel, cast or wrought cobalt, a metal-base alloy against a polyethylene (plastic)-lined acetabular cup.
Benefits
- Durable and versatile
- Long, successful clinical history
- Not toxic to the human body
- Adequate toughness for most lifestyles
Limitations
- May wear down over time, which can lead to inflammation, bone loss, and/or a revision procedure
Not all polyethylene bearings are manufactured and processed the same. DePuy Orthopaedics, Inc., developed AltrX™ AltraLink™ Polyethylene. In laboratory tests, the wear of AltrX™ AltraLink™ Polyethylene has demonstrated a 92% reduction in wear.1
Metal
When joint replacement began in the late 1960s, metal-on-metal bearings were the standard used in the United States. Although polyethylene was the most frequently used for many years, enhanced designs and increased demands from patients for stronger, longer-lasting implants have generated renewed interest in enhanced metal-on-metal technologies.
Benefits
- Range-of-Motion–allows for use of a larger femoral head providing for greater range-of-motion
- Stability-use of larger femoral head also lowers risk of dislocation
- Longevity-offers a lower risk of inflammation and implant loosening. Metal bearings are less likely than polyethylene bearings to:
- Release particles into the body
- Wear down over time2,3
Limitations
- May not be appropriate for those with metal sensitivity
One example of metal-on-metal technology is the Ultamet™ Metal-on-Metal bearings from DePuy Orthopaedics, an option used with Pinnacle Hip Solutions, which have over five years of successful clinical history.
Ceramic
Ceramic bearings are available in 2 configurations: a ceramic femoral head (ball) with a polyethylene liner, or a ceramic femoral head (ball) with a ceramic liner. No one material is right for every patient. Only your surgeon can determine what's right for you.
Benefits
- Reduced wear—improved lubrication and reduced friction4
- Performance—lower wear rates compared with polyethylene and metal4
Limitations
Ceramic bearings may be:- More prone to fracture
- Less forgiving in surgery
- More likely to require the removal of greater quantities of healthy bone due to size limitations
- More expensive than other bearing options
Next: Computer Assisted Surgery
References:
1. Liao Y-S, Greer, et al. Effects of Resin and Dose on Wear and Mechanical Properties of Cross-linked Thermally Stabilized UHMWPE. Society for Biomaterials, the 7th World Biomaterials Congress, Sydney, Australia, 2004.
2. Anissian H, et al. Metal-on-metal bearing in hip prosthesis generates 100-fold less wear debris than metal-on-polyethylene. Acta Orthopaedica Scandanavica. 1999;70(6):578-82.
3. Goldsmith A, et al. A comparative joint simulator study of the wear of metal-on-metal and alternative material combinations in hip replacements. Institution of Mechanical Engineers, Journal of Engineering in Medicine. 2000;214:39-47.
4. Ceramic-on-Polyethylene: Analysis of Results to Date. Seminars in Arthroplasty. 2003;14(2): 86-88.