Advances Make Hip, Knee Replacements Last Longer

New plastics, metals don’t wear out as quickly  
woman holding hip

Contributor: Michael Bloomfield, MD 

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Hip and knee replacements eliminate pain and improve movement for hundreds of thousands of people every year in the United States. Younger and more active patients are seeking joint replacements. This is why surgeons and implant developers continue to improve the prosthetics and techniques involved in the surgery.

In recent years, manufacturers have developed innovative plastics and metals that make the replacement joints even more dependable, durable and long-lasting. These new prosthetics will help these younger patients maintain their high activity level without pain.

 In the past, the plastic surface of the prosthetic device used in hip joint replacements often had a limited lifespan, usually due to two reasons:

  • The implant wears down, which sometimes caused the replacement hip to begin dislocating many years after surgery.
  • The implant emits microscopic particles, which the body tries to absorb. The body also may begin to digest bone – a process called osteolysis – which leads to a weakened bone, fracture or problems with the implant. 

If either of these two things happen, the patient should undergo a procedure called revision surgery to replace the implant. 

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Material improvements 

Over the last 10 years, manufacturing and processing methods of joint replacement parts have improved, resulting in longer-lasting joint replacements. 

A new kind of plastic, called highly cross-linked polyethylene, has greatly slowed the wearing out of the implants. The new plastic also virtually eliminates osteolysis for up to 10 years after the surgery. Laboratory studies using hip simulator models have shown that this material could last for decades.

Another major advance has been development of highly porous metals for use in revision surgery. Revision surgery is more difficult than first-time joint replacement because the failed prosthesis often causes bone loss. This can make it challenging to attach the new implant.

These new metals have greatly enhanced the remaining bone’s ability to grow into the implants, forming a secure bond that will last for a long time.

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Not all new technologies have been positive, however. Data shows that patients who have metal-on-metal hip replacements have higher rates of revision surgeries. 

On the way

The field of joint replacement continues to see better materials that promise better outcomes for patients. 

In knee replacement surgery, for example, manufacturers have introduced technology that produces instruments tailored to individual patients. Further improvements also are on the horizon for the metal surfaces through the use of advanced ceramic and oxidized zirconium. 

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