Dr. Bert J. Thomas, orthopaedic surgeon and chief of Joint Replacement Service at UCLA Medical Center, recently phoned in from California to discuss hip replacement surgery.
UCLA is ranked in the top 1 percent of all hospitals in the country by U.S. News & World Report. Its physicians are some of the best in the country, and it was one of the first hospitals in the country to perform hip replacements. As a world-class research hospital, UCLA is committed to advancing the science and technology of joint replacement.
Dr. Thomas is an award-wining surgeon with 30 years of experience in joint replacement surgery and is head of UCLA’s joint replacement program. One of his specialties is revising failed joint replacements, and he has helped more than 1,000 patients who have come from all over the world to seek his expertise in this area. The joint replacement program at UCLA often tackles some of the most complex surgeries, and a good portion of its patients are referred from other hospitals.
In the interview, Dr. Thomas graciously shares his vast knowledge about hip replacements. He explained the history of hip implant devices, particularly the science behind metal-on-metal implants and complications that can occur with these devices.
He also provides a fascinating look into the future of joint replacement surgery.
Hip replacement surgery improves lives; of this there is no doubt. The procedure has come a long way in the last few decades, and new technology has made implants more durable and safer.
“I have had patients (who had) been in wheelchairs for years,” Dr. Thomas said. “When you do the hip replacement, it’s a miracle for them. The pain is gone, and within a relatively short amount of time, they are up walking. And soon after that, they are back to being regular members of society.”
Back when hip replacement surgery was a younger technology, in the ’60s and ’70s, hips were replaced to take care of pain. Because implants did not last that long, younger patients were not candidates for the surgery. The functionality of the hip was not as good, and these cemented implants had a life span of about 10 years.
Now, the current implants can last up to 30 years and are used in patients much younger than 65.
“We’ve raised the bar substantially,” Dr. Thomas said. “Number one, we’ve allowed the procedure to go into younger and younger patients. And two, these materials that we are using now are so strong that we pretty much don’t restrict the activities.”
However, as with any surgical procedure, complications can still occur. Depending on the implant design, the prostheses can fail early – requiring additional hip surgeries called revision surgeries.
When a patient undergoes hip replacement surgery, this is called primary surgery or “index” surgery. A number of complications after primary hip surgery may require additional hip surgeries, which are known as revision surgeries.
Dr. Thomas explains that these surgeries are often more complex than primary surgery and require surgeons who have extensive experience and vast implant knowledge.
An implant may need to be revised (replaced) immediately if the patient develops an infection or dislocates the joint. An implant also must be replaced if it wears out, breaks or fails.
Most hips simply wear out after many years because of use. But some implants have above-average failure rates.
Metal-on-metal implants were designed to be more durable, but some of these implants began to fail early.
One implant, the DePuy ASR, reportedly has a failure rate of nearly 40 percent within five years. This means that almost half of patients require revision surgery shortly after primary surgery. The DePuy ASR was recalled in 2010.
Many experts – plus the U.S. Food and Drug Administration (FDA) – postulate that the rubbing together of the metal parts releases metal debris or ions into the tissues and blood, which can cause early implant failure and pain.
“In a small percentage of cases, if a metal surface rubs against another metal surface, it will release tiny metal ions, Dr. Thomas said. “For most patients, the ions will go into the blood stream and be excreted by your kidney.”
If you are one of the unlucky people who has a reaction to these particles, however, the complications can range from discolored, inflamed tissues to severe pain, swelling and loosening of the implant. An adverse reaction to the metal particles is called metallosis, which is a type of metal poisoning.
So, what causes some implants to release more ions or fail sooner than others?
“It turns out, the devil is in the details,” Dr. Thomas said. These details include design elements such as the locking mechanism, size of the implant and type of metal used.
Dr. Thomas said patients need to watch out for symptoms such as pain, swelling and noise in the hip, as these are often indicators that a metal-on-metal hip may need to be checked.
In order to check for tissue damage or excess metal in the blood, X-rays are usually a good indicator, since metal particles will show up in the films. But doctors also use blood tests and fluid tests.
Even then, no two patients have the same reaction to the particles. This makes treatment difficult. In most cases, the implant must be removed and replaced with a non-metal-on-metal alternative, such as a hip with ceramic or plastic parts in addition to metal.
At UCLA, the research continues into advancing joint replacement technology.
Dr. Thomas shared one exciting development. UCLA currently holds the patent on a polyethylene plastic that is incredibly durable and resistant to wear, and in simulation tests, no wear was registered even after the equivalent of 20 years. This plastic would be used with ceramic parts, eliminating the problem of metal ions.
Michelle Y. Llamas is a senior content writer and researcher for Drugwatch. She is also the host of the Drugwatch Podcast where she talks to patients, experts and advocates about drugs, medical devices and health. She uses her technical writing experience to provide easy-to-understand information on how drugs and devices work. But she also tells people what happens when products that are supposed to improve their lives can hurt them.
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