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And I'm David Greene.

Today in Your Health, we're going to look at a big problem with artificial hips. Millions of Americans have them and the vast majority work just fine. But thousands of people got a particular type of artificial hip that sometimes fails. For many, this means new rounds of surgery to fix the damage and replace the replacement hip.

NPR's Richard Knox reports.

RICHARD KNOX, BYLINE: Susan Mansfield - everybody calls her Susy - runs a recycling facility in her New Hampshire town. She used to climb mountains, kayak, even windsurf. But that was before her hip replacement back in 2009. It turns out the model she got was poorly designed, which is why she now finds herself in an operating room at Massachusetts General Hospital. Surgeon Young-Min Kwon stands above her. He's dressed in a moon suit, his face behind a plastic shield. Once Mansfield's under anesthesia, Kwon's scalpel soon exposes the problem caused by Mansfield's faulty hip implant.

DR. YOUNG-MIN KWON: There's a yellowish discoloration of the tissue that is no longer functioning.

KNOX: The yellow tissue used to be Mansfield's muscle. The all-metal artificial hip she got nearly three years ago has been killing it. Next, assisting surgeon David Anderson takes up a mallet and knocks off the implant's steel ball at the top of her thigh bone.

DR. DAVID ANDERSON: I just disengaged the head from the stem.

KWON: So that's all dead tissue.

KNOX: The doctors are finding more dead tissue than they expected. Over the next couple of hours, they're going to have to take out most of the old hip and replace it with a new artificial joint.

Good to see you.

SUSAN MANSFIELD: You too. Nice to meet you.

KNOX: A few days before the surgery, I visited Susy Mansfield at home.

MANSFIELD: Set yourself down here for the moment.

So, what sort of tea do you like?

KNOX: Over elderberry tea, she talks about how her hip problems began. It was on a wintry day nine years ago, when she was 52.

MANSFIELD: So, there's ice in the winter. I slipped on the ice and I fell and landed on this hip.

KNOX: She didn't break the hip. She got up and kept going.

MANSFIELD: You know, this is New England, where you buck up, don't fuss, keep going.

KNOX: As months and years passed, the pain didn't go away. In fact, it got much worse. A little over three years ago, an orthopedic surgeon told her she needed a hip replacement.

MANSFIELD: He said: You're young. I was 57. And he said: We're going to use a metal hip. Metal is good for younger people. It's going to last longer.

KNOX: The all-metal hip was a new idea. Older models were made of tough plastic and metal. But those can wear out over 10 or 15 years, especially in patients who are young and active. Surgeons got excited about the all-metal joint because they thought it was the answer to that problem.

By the time Mansfield got her implant, one in three artificial hip patients across the nation was getting this kind. That's tens of thousands every year. But months after the implant, Mansfield still had hip pain. And she had a strange feeling that her joint would suddenly slip.

MANSFIELD: In fact, at one point, the doctor said: OK, I'll hold your hands. He put his fingers out like this and I held his hands. Now stand on that leg. And I stood and it went kachink, like that. And he said, what the hell was that?

KNOX: The doctor told her to lose weight and be more faithful about her physical therapy. But the pain just got worse.

MANSFIELD: It's terrible. It's a hot pain. This is a pain that's here all the time. Every step is agony. Every step is painful.

KNOX: Then she read something about problems with all-metal hips. So she immediately called her surgeon.

MANSFIELD: And I said I read a piece in the paper and I want to know if this really is the hip that I have.

KNOX: The doctor's secretary told her she didn't have one of the problem hips. But she checked around and found out, in fact, she did. Not only that, but her model had actually been recalled by the manufacturer.

MANSFIELD: This is a lot for me to take in. But holy moley. You know, this is a big thing here.

KNOX: She did some research and found out that her new hip was actually doing her harm.

MANSFIELD: Once you learn about this hip, every step you take releases more metal debris. You have something that's actively making you worse.

KNOX: Eventually, she found her way to Dr. Kwon, the Boston surgeon whom we heard earlier in the operating room. He set up a special center for patients with faulty hip implants. He operates on patients like Susy Mansfield several times a week.

MANSFIELD: He sat down with me and he said, I can't promise you 100 percent. I think I can get you 85 percent better. I said, I'm already at a place where I'm trying to figure out how I'm going to live with this. If we can't fix it, then I'm at the end of the line. What am I going to do?

KNOX: So, Mansfield decided to go ahead with this surgery and get the old implant replaced. It's a big operation. Thousands of people are having this so-called revision surgery. Precise numbers aren't available. By this point in the operation, Kwon has removed part of the faulty implant. He points out a black stain on her tissues where the old implant was.

KWON: You see that staining? Black staining of the tissue from the metal?

KNOX: Is that metal debris?

KWON: Yes, so we call that metallosis.

KNOX: Metallosis means the buildup of metal debris. Tiny pieces of cobalt and chromium have flaked off the implant and worked their way into surrounding tissue. That's caused swelling and tissue death and the pain that kept Mansfield awake at night.

(SOUNDBITE OF TAPPING)

KNOX: Next, Kwon takes the mallet, removes the implant's metal cup from Mansfield's hip bone and holds it up for me to see.

KWON: There's actually no bone that's grown into this.

KNOX: What should it look like?

KWON: It should be covered with the bone.

KNOX: So the bone never did what it was supposed to.

KWON: No.

KNOX: Mansfield's own bone cells never grew into the implant like they should have. That's why she always had the sense it was loose and prone to slip - that ka-chink sensation.

KWON: We'll definitely use the bone graft. If you can open up the bone graft.

KNOX: They need to do a bone graft to beef up the hip bone under her implant. It's grown thin - another effect of the all-metal joint. Kwon sprinkles white pieces of bone taken from a cadaver donor into the hollow where the old implant used to be. The pieces will grow together and fuse with her own bone.

KWON: There's a lot of areas where the bone is actually missing. We're reconstituting some of the bone that she lost.

KNOX: Fortunately, Kwon doesn't have to take out the shaft of the old implant imbedded in her thigh bone. And after several hours the operation's finished.

What kind of result do you think Mrs. Mansfield can expect?

KWON: I think she has a reasonable prognosis.

KNOX: One big problem with the type of hip implant Susy Mansfield got was that it didn't have extensive testing in humans before it went on the market. It was approved through Food and Drug Administration rules that didn't require human studies. Kwon says that shouldn't happen in the future.

KWON: I think there are lessons for all of us, that you need to have scientific data to support any introduction of any new technology.

KNOX: And did this one have enough?

KWON: One might argue that it didn't have enough.

KNOX: Fortunately, most patients who got metal implants don't suffer the kind of damage Mansfield did. Dr. Joshua Jacobs is a Chicago surgeon who's an officer of the American Academy of Orthopedic Surgeons.

DR. JOSHUA JACOBS: Most patients that have metal-on-metal bearings are doing fine. They have good clinical results. Even the implant that's been recalled, the majority of patients still have well-functioning implants. However, it does have a failure rate that is unacceptably high.

KNOX: Nobody really knows how high. A British study that's just been released found that one in 16 of these implants failed within five years. But the rate could be higher. In this country, there's no way to keep track of how many were implanted or what happened to the patients.

The FDA says patients with all-metal implants should be monitored for problems. Four days after her surgery, Susy Mansfield is almost ready to go home.

So, how are you feeling?

MANSFIELD: Just a little woozy at the moment because I'm still doing pain meds. But, you know, pretty good.

KNOX: Remarkably, she's already passed a crucial test - going up and down stairs on crutches. And she's full of hope.

MANSFIELD: I'm going to actually be able to, I think, and fairly soon, have no pain.

KNOX: She promises to follow doctors' orders, take precautions, eat sensibly, and do her physical therapy.

MANSFIELD: I did all of that the last time too. But this, I have reason to believe, is not a bad hip. And the other one was a bad hip.

KNOX: In a few months she hopes she'll be back to taking her dog for long walks again.

Richard Knox, NPR News, Boston.

(SOUNDBITE OF MUSIC)

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