What Are Hip Replacements Made Of?

Hip replacement surgery involves replacing the worn-out bone and cartilage lining your hip joint with new implants that are composed of materials such as ceramic, metal and plastic.

Over the last two decades, the number of total hip replacements being performed each year has steadily increased in the United States. Accompanying this boom in surgery has been the release of information via the news, social media, documentaries and internet. If you’re considering hip replacement surgery, it’s best to be informed by reliable sources about what is being placed inside of your body. AAHKS has created this guide to provide all the information and research related to materials used in hip replacement surgery.

Total Hip Replacement Materials

Standard total hip replacement implants are typically made up of approximately four individual components (see Figure 1 below):

1. Stem—inserts into the femur or thigh bone
2. Cup—inserts into the pelvic bone
3. Ball—fits onto the end of the stem
4. Liner—inserts into the cup—essentially becomes your new cartilage

The Stem

The femoral stem is the portion of the replacement that fits into your thigh bone. Historically, this is made from cobalt-chromium and/or titanium metals. In the modern era of hip replacements, cemented stems (inserted with an epoxy bone cement) are composed of cobalt-chromium metals. Cementless stems (implants in which your bone grows into the metal) are routinely made of titanium. Both designs have had excellent long-term results as part of total hip replacement systems.

• Both titanium and cobalt-chromium implants are considered highly biocompatible—meaning they are generally well tolerated by the human body with low risk of adverse reaction. In fact, both materials have been shown to be highly effective in adhering to bone.
• The top end of the femoral stem (called the trunnion) is specially shaped to hold the new ball of the artificial joint. Regardless of the material that the ball is made out of, this is where the head and stem fit together.

The Cup

The acetabulum (cup) structure fits into your pelvis and is also made from various metals. The majority of modern cups are made from titanium or tantalum metals. Both metals are well tolerated by human bone and serve as excellent surfaces for bony attachment.

• The metallic cups serve to hold the liner of the hip replacement, which essentially serves as a replacement for cartilage.
• In rare cases, the plastic liner may be used without a metallic cup and is held in place using an epoxy bone cement.

The Ball

The femoral head (ball) fits on the end of the stem (trunnion). This end of the stem is taper shaped to allow the ball to wedge into position and be held tightly in place with friction. The ball comes in varying diameters often related to the size of the cup that fits into the pelvis. The ball can be made from different materials:

• Ceramic—Many refer to this as a porcelain type material. This is a very hard surface and is extremely resistant to scratching or other damage. Ceramic heads can be paired with either ceramic or plastic liners.
• Cobalt-chromium—For the better part of the last three decades, this has been the most common material used for the ball as it is relatively-scratch resistant and holds up well (similar to ceramic described above). Cobalt-chromium heads can be paired with plastic or metal liners. Due to some potential concerns for metal debris formation when cobalt-chromium heads are paired with metal liners recently brought to light, cobalt-chromium heads are now most commonly used with plastic liners instead of metal liners.

The Liner

The acetabular liner fits into the cup and serves as your new cartilage. Much like the cartilage in your own hip, it is susceptible to wear and historically this has been the “weak link” of total hip replacement. Early forms of the liner were subject to wear by making contact with the ball and were thought to last only about 10 years. Modern day improvements have made liners last longer by either using alternative materials or strengthening the plastic.

• Ceramic—As mentioned above, ceramic is a very strong material and provides low wear rates when coupled with a ceramic ball (“ceramic-on-ceramic”).
• Cobalt-chromium—Metal liners have fallen out of favor when used with metal balls over the last 10 years; however, newer options where a plastic ball is placed in a metal liner (known as dual mobility) have shown excellent short-term results in the United States and may be useful when utilized in specific patients.
• Polyethylene—Plastic is by far the most common material used for hip replacement liners. This material has provided good to excellent results when paired with ceramic or cobalt-chromium balls. Recent advances in the manufacturing of polyethylene have significantly improved the wear rates of these plastic liners over the last 10-15 years.

When it comes time for a total hip replacement, you should discuss with your surgeon the options and pros and cons of each material. Together you can make the best decision for your particular case. While no surgical procedure is risk free or guarantees 100% success rates; remember total hip replacement is one of the most successful procedures in all of orthopedics. Many studies have shown hip implants can last beyond 15 years from the original surgery.

Long-Term Outlook

As we continue to pursue perfect hip replacements, there are likely to be some designs and materials that perform better than others. The bulk materials used to make hip replacements are quite similar and have not changed drastically in the last 30 years. Reaction and complications directly related to the materials themselves, while possible, are not common as manufacturer guidelines and standards are strictly followed and monitored.

The majority of total hip patients can anticipate long-term success somewhere between 80-85% at 10-15 years after the surgery.

Despite recent concerns for the metals and materials used in hip replacement, the vast majority of these procedures lead to successful outcomes with improvement in patients’ quality of life and function.

Talk to Your Surgeon

AAHKS recommends discussing implant options with your surgeon to gain an understanding of the particular materials to be used in your surgery.

Discuss with your surgeon the risks and benefits of different implants and materials to gain an understanding of the proposed procedure.

Developing a good relationship and level of trust with your surgeon is a key aspect of ensuring a successful outcome.

In the end, your surgeon is looking out for your best interests, and as much as you trust an airline pilot and the flight plan they follow, you should have the same trust in your surgeon.

Frequently Asked Questions about Hip Replacement Materials

What is the chance of my body “rejecting” the implant?

Unlike an organ transplant, the risk of your body rejecting the artificial hip parts is exceedingly rare. The materials used in the typical replacement surgery are well tolerated by the body and have a long track record of successful implantation. While in rare cases the parts may become loose or infected, this is typically related to other factors and not due to your body “rejecting” the parts.

How do I know if I have a recalled implant?

Most modern hip replacement parts have a long history of excellent safety and few known mechanical issues. In recent years, there have been a handful of very specific implants involved in a recall process due to metal reactions, higher than expected failure rates and other unanticipated problems.

Most companies offer numerous models and designs of their implants (like the car makers and the different makes and models they offer). It is important to keep in mind that just because one model has been recalled, the company is likely to have many others that are performing very well.

The vast majority of patients will not experience an issue with a recalled implant. If you are concerned about your particular type of replacement, we recommend you contact your surgeon’s office to ensure that your implant has not been involved in a recall.

I have a history of nickel allergy and/or break out in a rash with certain types of jewelry. How do I know if I am allergic to the implants?

The metals used in hip replacements are generally well tolerated by the body, even in patients who have skin sensitivity to certain metals (this type of allergy involves a different part of your immune system).

For more detailed information, please see the FAQ on metal allergy and joint replacement.

How do I know if I have developed metal poisoning from the replacement parts?

While recent concerns have been raised about the potential for developing metal poisoning (cobalt or chromium toxicity) from hip replacement parts, such cases are thought to be exceedingly rare. In some cases (typically associated with very specific models of hip replacement – most of which are no longer used by surgeons), excessive levels of metal ions may be generated by the implant surface contact points. These metal ions may in turn cause a reaction in the tissue around the joint and can, in isolated cases, lead to tissue and/or bone destruction.

If your implant is functioning well and you have little pain or change in comfort level, chances are you are at very low risk of a metal reaction.

If you are experiencing new or worsening pain, contact your surgeon to be evaluated. Again, cases of metal poisoning from orthopedic implants are very rare and generally occur in the tissues around the joint involved. While in theory hip implants can lead to elevated levels of metal ions in the blood, systemic side effects of metal poisoning from joint replacements (kidney damage, neurologic symptoms, psychosis) are exceedingly rare.

Can I have a hip replacement if I am allergic to metal?

Yes, you can still have a hip replacement if you are allergic or sensitive to metal. Metal reactions are very rare. If there is a concern about metal allergy this is an individual discussion to have with your surgeon

Testimonials

Once An Athlete, Always An Athlete – William Best

I’ve been an athlete all my life, but at age 69 was beginning to find it hard to do some of the activities I had grown fond of doing. These included skiing, horseback riding and golf. Osteoarthritis in my hip had begun to restrict my ability to twist. I decided to meet with Dr. Rafael Sierra at Mayo Rochester to discuss the possibilities of a hip replacement. During our meeting, we discussed in detail the anterior versus posterior approach to the procedure. The anterior approach seems to be the most preferred procedure these days, but with that, there’s the possiblity of causing damage to the nerve bundle located near the incision. This was a concern for me. To read more, click here.

I Feel 10 Years Younger – Greg Bland

My doctor had recommended total knee replacement in 2017, but I was under the belief that I was too young (54) and that the replacement wouldn’t last very long. When the viscosupplementation finally wore off I couldn’t walk even one block before intense pain kicked in. Because of COVID-19 related delays, it took five months before I could get “elective” surgery. To read more, click here.

Expectations and Advocacy from a Well-Known Bioethics Professor – Dr. Arthur Caplan

AAHKS Patient and Public Relations Committee Chair, Dr. Brett Levine spoke with Professor and founding head of the Division of Medical Ethics at NYU Grossman School of Medicine in New York City, Dr. Arthur Caplan. Dr. Caplan had joint replacement surgery on his right knee after experiencing pain to the joint and trouble walking up stairs. From his medical school training, Dr. Caplan knew something was wrong with his knee, so he went to have it examined. Immediately upon seeing the x-ray, Dr. Caplan knew he was a candidate for knee replacement surgery. «I’m so fortunate I went early to have my knee examined, because you create more damage the longer you wait.» To find out more, click here.

Years of Damage, Repaired in Hours – Rachael Epling

After being in a car accident 21 years prior, Rachael Epling decided to take her life back. As one who loves to be active, the pain she was experiencing limited her physical activities. After receiving multiple cortisone injections, trigger point injections, and radiofrequency procedures on her lower back to reduce the pain, Rachael made the toughest decision of her life. At age 42, she underwent a Total Hip Replacement via the anterior approach. It wasn’t easy, but after spending half her life in pain, she was determined to get her life back. To find out more, click here.

It’s all about «Work Mode» – Michelle Menconi

Michelle Menconi decided to undergo a total knee arthroplasty procedure on her right knee almost one year ago. Michelle slowly started to see her quality of life being limited due to the pain she was experiencing in her right knee. She noticed it about five years ago. To help with her deteriorating knee, she was given cortisone shots and for three weeks straight, Michelle had lubrication injected into her knee. Michelle knew it was time to do something, so she went into «work mode,» handling this situation like a business transaction – doing the research to find the right surgeon for her, finding out the best way to get the surgery done, best way to recover and what she wanted long-term for her knee. To find out more, click here.

The Grateful Golfer – Rev. Dr. George B. Wirth

In March of 2017, thanks to the reference of a close friend, I flew to Little Rock to meet with, Dr. C. Lowry Barnes and his medical team to explore knee replacement for both of my knees. As a former college/graduate school rugby player for seven years in Chapel Hill, NC and Princeton, NJ, squash player and a 10K runner for 45 years, both of my knees were in bad shape. The pain had become debilitating, I had difficulty sleeping at night and walking during the day and knew that something had to be done. To read more, click here.