The Basics of Total Hip Replacement Surgery

1. Elimination of pain
   
   
2. Improved motion
   
   
3. Minimum wear and tear

During a total hip replacement procedure a metal stem is inserted into your thighbone (femur). Attached to the neck of the stem is a hip ball, just over an inch in diameter. The hip ball fits into a liner. Together, the ball and liner create the new joint. The liner is inserted into a metal shell that in turn is anchored to your pelvis. In terms of fixation, your surgeon has the choice of anchoring the hip implants securely to bone using either cement fixation or fixation by 'bone ingrowth'. Your surgeon will select the design of the hip replacement and size of femoral ball to give you the range of motion and stability that you need to function.

Your body has to cope with any wear debris that is released when you use your hip implant, unlike your car engine that has special filters to remove the wear products.  The standard metal ball and polyethylene cup have been in use for over 40 years.  In younger, more active patients, there is a propensity for the metal ball to become scratched.  Scientific studies indicate the use of improved polyethylene liners, called ‘highly crosslinked’ bearings, result in overall decreased wear of the implant.

Ceramic-on-Ceramic (Stryker Orthopaedics)

If you are a very active individual or a relatively young patient, your surgeon may prescribe an all-ceramic hip joint. Such all-ceramic hip joints have been used in Europe for over 30 years but have only recently received the FDA’s approval for marketing in the United States.

In these hip joints the traditional metal ball and polyethylene liner are replaced by a high-strength ceramic bearing that has the reputation for ultra low wear performance.  The implant to the right shows the stem, the ceramic ball (Biolox Forte), and the ceramic liner, which is wrapped in metal to ease its fixing to the metal shell.  Clinical studies, monitored by the FDA and begun in 1998, have demonstrated excellent performance.

Choices of Implant Material
Polyethylene, Metal, or Ceramic? 

One of most common problems with replacement hips is the wear and tear that takes place through normal use. Over time, the body may see polyethylene wear particles as invaders or a source of infection. As the body starts to attack them, this leads to osteolysis, a "dissolving of the bone", which may result in having to replace the implant (revision). If you are a very active individual or a relatively young patient, your surgeon may prescribe an all-ceramic hip joint or all metal hip joint. Depending on the size of your natural hip, the surgeon also has the option of selecting 28mm or 32mm diameter ceramic balls or even larger metal balls. As of 1999-2003, the FDA has approved for market larger all-metal and all-ceramic hip replacements as alternate bearings to the polyethylene liner.

Metal Ball and Polyethylene Liners

Metal-on-Polyethylene (Zimmer Orthopedics)

Because of its durability and performance, Metal-on-Polyethylene has been the leading artificial hip component material chosen by surgeons since FDA approval 30 years ago. The metal ball is cobalt chrome molybdenum alloy and the liner is polyethylene.  Polyethylene is the most understood and used of all the liner materials, offering the surgeon a range of options to obtain stability in the body while the operation is underway.

This ability to adapt and customize during the surgical procedure is an important attribute of polyethylene.  It is also the least expensive bearing.

All implants shed wear debris.  The most active patients shed the most debris, and with polyethylene this may show up after 10 to 15 years, resulting in joint inflammation and bone loss.  As a result, new wear resistant polyethylene liners have been introduced, called “highly crosslinked polyethylene.”   During the manufacturing process the plastic is treated with a short burst of radiation to help the cup resist wear.  

Wear rates: Metal-on-Polyethylene implants wear at a rate of about 0.1 millimeters each year.

Ceramic Ball and Polyethylene Liner

Ceramic heads are harder than metal and are the most scratch resistant implant material. The hard, scratch resistant, ultra-smooth surface can greatly reduce the wear rate on the polyethylene bearing.  The wear rate for this type of implant is less than Metal-on-Polyethylene. 

Ceramic-on-Polyethylene Vitamin E stabilized liner (Biomet Inc.)

Ceramic-on-Polyethylene is more expensive than Metal-on-Polyethylene, but less than Ceramic-on-Ceramic.  In the past, there had been incidents of fractures, but newer, stronger ceramics have resulted in considerable reduction of fracture rates (0.01%) compared to the original brittle ceramics.

The implant shown to the right utilizes vitamin E stabilized highly crosslinked polyethylene bearing material. Vitamin E, a natural antioxidant, is expected to improve the longevity of the implant bearings used in total joint replacements. In laboratory testing, these liners have demonstrated 95-99% less wear than some other highly crosslinked polyethylene liners.

Wear rates: Ceramic-on-Polyethylene implants wear at a rate of about 0.05 millimeters each year, i.e. 50% less than Metal-on-Polyethylene. The newer, highly crosslinked polyethylene liners have shown wear rates as little as 0.01 millimeters each year.

Metal Ball and Metal Liner

Metal-on-Metal (Zimmer Orthopedics)

Metal-on-Metal bearings (cobalt chromium alloy) were approved by the FDA in 1999, offering the potential for greatly reduced wear, with less inflammation and less bone loss.  Metal bearings are available in many sizes (28 mm to 60 mm); there are also several neck lengths available. Large ball heads provide increased range of motion and greater stability, which can significantly reduce the risk of hip dislocation, a crucial factor in the long term success of an implant.

The metal liner can be used by itself, or a conventional polyethylene liner may have a cobalt chrome metal inlay as shown here. 

Although wear is reduced, the wear products (sub-microscopic particulates, soluble metal ions) are distributed throughout the body.  This has raised concerns about long-term bio-compatibility.  At present these are only concerns, for there have been no definitive clinical findings that these wear products are harmful.

Anatomic Size Metal-on-Metal Ball Heads

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Metal-on-Metal Big Femoral Head BFH® Technology Comparison (Wright Medical)

Because the human femoral (ball) head is naturally large, it makes sense to implant a large, anatomic replacement. This was not possible in the past because traditional polyethylene liners made smaller femoral heads necessary. However, with the introduction of metal-on-metal implant components, liners may be eliminated, allowing surgeons to use large femoral heads. The image on the right illustrates the difference between the ball head size of a traditional implant versus the larger ball head. Use of a larger ball head has been shown to increase the range of motion an individual may experience as well as decrease the possibility of dislocation.

Wear rates: Metal-on-Metal implants wear at a rate of about 0.01 millimeters each year.

Ceramic Ball and Ceramic Liner

Ceramic-on-Ceramic (DJO Surgical)	Ceramic-on-Ceramic (DJO Surgical)

Ceramic-on-Ceramic implants have been used in Europe for more than 30 years, and since 2003 in the United States. Ceramic is the hardest implant material used in the body, and has the lowest wear rate of all, to almost immeasurable amounts (1000 times less than Metal-on-polyethylene). Consequently, there is usually no inflammation or bone loss, nor systemic distribution of wear products in the body.  New ceramics offer improved strength and more versatile sizing options.

The Ceramic-on-Ceramic implants shown to the right have design features that provide your surgeon with several fixation and alignment options.

Wear rates: Ceramic-on-Ceramic implants wear at a rate of about 0.0001 millimeters each year.

Your next step: Print this page and discuss these options with your surgeon, or use our Clinic Locator to find a orthopedic clinic in your area.

We also invite you to visit our Public Forum to discuss options and share experiences with others.

A note about Manufacturers and their Products The BoneSmart® mission is to provide consumers with easy to understand un-biased information about joint replacement materials and patient options. However, it is important to note that each of the major manufacturers of joint replacement implants promote variations in design that make each of their products unique in some fashion. We encourage you to spend some time exploring manufacturer product offerings via their respective websites. Use the information you obtain from this research to discuss with your surgeon which particular implant might be best for you. The major joint implant manufacturers are: Biomet, CeramTec, ConforMIS, Inc., DJO Surgical, Wright, Stryker and Zimmer

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This website provides patient awareness as it pertains to new and enhanced materials for hip or knee implant surgery.  It is important to note that no specific implant material is right for every patient.  The purpose of knowing your implant options is so that you, the potential candidate for implant surgery, will have an awareness of your options so as to discuss these choices with your surgeon. Implant images are provided courtesy of various orthopedic manufactures and are rotated without favor from time to time. Please return periodically to this site for updates.