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.

Image Susan OToole noticed an odd sound as she went up stairs. Credit... Chester Higgins Jr./The New York Times

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.”