That Must Be Bob. I Hear His New Hip Squeaking.

Right, Dr. William Walter

Susan O’Toole’s artificial hip developed a squeak, a problem with ceramic parts. Used components show areas of friction.

The first time John L. Johnson’s artificial hip squeaked, he was bending down to pick up a pine cone in his yard in Thomasville, Ga. Mr. Johnson looked up, expecting to find an animal nearby.

Susan O’Toole, a nutritionist at Montefiore Medical Center in the Bronx, who first squeaked going up stairs after getting home from her hip-replacement surgery in 2005, said she thought the banister she was gripping needed repair.

And Edward Heary, an apprentice appraiser in Hatboro, Pa., said clients sometimes look with embarrassment or concern at their floorboards when he walks though their homes.

As all three patients — and hundreds of others — discovered once they pinpointed the source of the noises, they had become guinea pigs in an unfolding medical mystery. Their artificial hips are made of ceramic materials that were promoted as being much more durable than older models. But for reasons not yet fully understood, their hips started to squeak, raising questions about whether the noises herald more serious malfunctions.

“There is something amiss here,” said Dr. Douglas E. Padgett, chief of adult reconstructive and joint replacement service at the Hospital for Special Surgery in New York. More than 250,000 Americans get total hip implants each year, a procedure that generally costs close to $45,000. Hip replacements have a success rate of more than 90 percent, based on patients’ achieving relatively pain-free mobility after recovery periods that range from a few months to a year.

Any artificial hip can occasionally make a variety of noises. But until Stryker, a medical products company, began marketing highly durable ceramic hips in the United States in 2003, squeaking was extremely rare.

Now, tens of thousands of ceramic hips later — from Stryker and other makers that entered the field — many patients say their squeaking hips are interfering with daily life. One study in the Journal of Arthroplasty found that 10 patients of 143 who received ceramic hips from 2003 to 2005, or 7 percent, developed squeaking. Meanwhile, no squeaks occurred among a control group of 48 patients who received hips made of metal and plastic. “It can interrupt sex when my wife starts laughing,” said one man, who discussed the matter on the condition that he not be named.

Beyond annoyance and embarrassment, many patients and their surgeons fear that the squeaky ceramic hips may signal that the joints are wearing out prematurely. That could force patients to undergo the very operation — a second replacement of the same hip joint — they had hoped to avoid by choosing ceramics.

Already, dozens of patients have elected to endure subsequent surgeries to replace the noisy hips. Some have sued Stryker, the pioneer and market leader, which some doctors say has been slow to take their patients’ concerns seriously.

Last fall, the Food and Drug Administration issued a warning to Stryker, saying it had failed to take the steps needed to prevent squeaking and other problems. Clouding things further, Stryker last year recalled ceramic hip parts made at its factory in Cork, Ireland, after determining that some did not meet its sterility specifications.

Stryker says that none of the problems underlying the recall or the warning letter from the F.D.A. reflect problems that cause squeaking, which it contends occurs in less than 1 percent of implants.

Whatever the actual frequency, some investigators who have looked at the problem say the squeaking seems to be associated with extreme flexing of the ceramic implants, but exactly how is unclear. In X-rays, many of the squeaking hips appear to be perfectly aligned. Nor is there a clear relationship between squeaking and hip pain or other conditions some patients say they have encountered, like the sensation that the hip disengages slightly when a patient walks.

Some patients squeak even they are walking normally, like Ms. O’Toole or Michael Mueller, a software executive in Scottsdale, Ariz. Mr. Mueller is so frustrated with squeaks, pain and popping noises for which he blames his ceramic hip that he has displayed his problem on YouTube.

While there have been no reported cases of serious mishaps, some surgeons fear that the ceramic material might shatter at some point, leaving a patient with so many inflammatory shards in the hip that a doctor could never find them all.

“Catastrophic failure has been a concern in the past, with older ceramic components,” said Dr. James M. Bried, a surgeon in Poway, Calif. Ceramic materials have been used since the 1960s. Dr. Bried, who implanted Mr. Mueller’s hip last year, said he was concerned that squeaking might be “a harbinger of something similar.”

Mr. Mueller said Dr. Bried had told him to consider getting the hip replaced “sooner rather than later.”

Stryker says such fears are overblown.

“It is important to keep this in perspective,” said Aaron R. Kwittken, a spokesman for Stryker. “Published research shows squeaking is rare compared with other total-hip-related risks like infection, dislocation and leaving patients with uneven leg length.”

But plaintiffs lawyers, who have already filed scores of lawsuits on behalf of ceramic hip patients, are gearing up to argue that squeaking is not a minor problem for many who experience it.

“We’re in the infancy of this,” said Douglass A. Kreis, a personal injury lawyer in Pensacola, Fla., whose clients include Ms. O’Toole and Mr. Johnson, who has had his ceramic hip replaced.

Most artificial hips, whatever material they are made of, share a basic design: a socket implanted in the pelvis, into which a spherical head is fitted. The head is attached to a spike that is driven into the femur, or thigh bone, to anchor it.

Durability is paramount with artificial hips. Patients worry that they will outlive their artificial hips and require a second, more extensive and even more expensive procedure at an age when their bodies may be less able to cope with the trauma. Ceramic hips were promoted as lasting much longer than the 15 years or so for conventional artificial joints made of steel and plastic.

Now that the squeaking has raised caution flags, researchers are weighing the noted durability of ceramic-on-ceramic hip joints like Stryker’s Trident model against products with other combinations of materials.

Each combination has known or suspected drawbacks. Metal-on-metal devices, for instance, slowly shed tiny ionized particles that some researchers say might promote cancer. And even the newest plastics are still not as durable as other materials, raising the risks of fragments that can lead to bone-destroying inflammations.

For patients who have already received ceramic hips that have started to squeak, many orthopedic surgeons advise nothing more than watchful waiting unless there are also signs that the hip is slipping out of place or that ceramic particles are breaking loose from the head or the socket. Doctors who have removed ceramic hips say they find dark stripes that indicate accelerated wear on the ceramic heads. But durability tests have suggested that even those extracted hips would have outlasted conventional metal-and-plastic replacement joints, according to researchers.

“There is no evidence that the wear associated with squeaking would lead systems to fail,” said Dr. James A. D’Antonio, an orthopedic surgeon outside Pittsburgh, who was a chief investigator on the clinical trials that led to regulatory approval for Stryker’s Trident.

Dr. D’Antonio, whose longstanding role in Stryker’s product development efforts earned him $1.1 million in consulting payments from the company last year, said he had implanted 400 Tridents since the clinical trials began in 1996. He said that only four of his patients had noticed squeaks and that none of them were able to reproduce them in his office.

But Dr. Fabio Orozco, a surgeon at the Rothman Institute, a major orthopedics group in Philadelphia, said that a recently completed review of about 1,500 Rothman patients with ceramic hips had found that the squeaking condition occurred in 49 of them, or about 3 percent.

“I’m very hesitant to use ceramic-on-ceramic now,” Dr. Orozco said, “unless we are talking about somebody very young.”

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