SACRAMENTO, Calif. By his early 60s, Michael Stieler had worn out the cartilage in his right hip with a lifetime of running, hang gliding and carpentry work. Surgery to replace the hip in 2007 provided enormous relief for the Sonora, Calif., man - for a year.

"And then all heck broke loose," said Stieler, now 68. "It hurt. I couldn't even walk on it."

He and his wife, Darlene, weren't surprised when a notice arrived last September from the company that manufactured his artificial hip, DePuy Orthopaedics: His all-metal hip was being voluntarily recalled because of its early failure rates as well as its potential for shedding high levels of cobalt and chromium into the bloodstream.

Now the Food and Drug Administration has ordered all 21 companies that produce so-called "metal on metal" hips to monitor recipients, assessing how they react to the implant. And thousands of artificial hip recipients are wondering if they're at risk from their new hips.

"The crux is, we've seen some of these implants fail very early and exhibit metal ion release," said Dr. Thomas Blumenfeld, an orthopedic surgeon at Sutter Orthopaedic Institute in Sacramento. "But the vast majority of implants will do well."