If your knees creak and pop, the noises could be an indicator of early arthritis, even if the joint does not hurt, according to one of the first long-term studies of the association between noisy knees and joint disease.

But not every creaky knee is diseased, the study also finds, making it important to try to discern what your particular knee noises may mean.

For many of us, developing grinding, popping or creaking sounds in our knees can seem almost like a rite of passage into middle age. Tens of millions of people over the age of 40 report that they at least occasionally hear noises in their knees, a condition that in medical circles goes by the ominous name of crepitus.

Researchers and clinicians have long been undecided about whether the onset of knee crepitus also signals the beginnings of arthritis, with its slow but relentless deterioration of cartilage and bones, or if the noises are annoying but otherwise benign.

The results of past studies of associations between crepitus and arthritis have been conflicting, with some indicating a strong likelihood that someone whose knees pop also has underlying arthritis and others showing little consistent relationship. Many of these studies, however, looked at people's knees at one point in time, leaving the fundamental relationship between crepitus and the onset of arthritis, especially over the years, in doubt.

So for the new study, which was published this month in Arthritis Care & Research and funded primarily through the National Institute of Arthritis and Musculoskeletal and Skin Diseases, part of the United States National Institutes of Health, a group of researchers from the Baylor College of Medicine in Houston and other institutions decided to focus on the long-term health and creakiness of the knees of almost 3,500 participants in the ongoing Osteoarthritis Initiative.

This large-scale, national study has enrolled thousands of adults at risk of developing arthritis because of their age, body mass or other factors. (Being older than 45 or overweight greatly increases the likelihood of knee arthritis.) These men and women have visited a lab annually for at least four years for a knee X-ray and an exam that includes questionnaires about joint pain and how often, if ever, their knees creak, grind and pop.

The researchers chose records about people who had not yet developed full-on knee arthritis, which the scientists defined as having both frequent knee pain and an X-ray showing bone spurs. People included in the new study could have a spur-riddled X-ray but little or no knee pain or a badly aching knee with a clear X-ray, but not both. The researchers also checked to see whether these people reported instances of crepitus sometimes or often.

Finally, they gathered the same information for a year after someone first joined the original study and again at the end of four years. Then they compared the state of people's knees over that time and looked at the associations, if any, with crepitus.

Overall, most people's knees did not worsen significantly, especially during the first year that someone was in the study. About 18 per cent of the studied joints progressed from showing suggestions of arthritis - pain or a worrisome X-ray - to having the full spectrum of both aches and a spur-ridden X-ray.

Many of the people in that 18 per cent also had reported having crepitus at the start of the study.

The instance was especially large among people whose knees had shown X-ray evidence of arthritis but who had not reported much joint pain. In that group, crepitus was a clanging alarm; the creaks and pops strongly indicated that they would develop more severe knee disease after a year or four.

But that was not true for everyone with crepitus. For some, their knees stayed stable over the years.

The upshot is that the exact nature of the relationship between knee noises and knee health remains enigmatic, says Dr Grace Lo, an assistant professor of medicine at Baylor who led the study, and it still is not clear what produces those sounds in the joint.

But in general, popping and creaking merit an appointment with your physician, she says, since there was clearly an association in this study between the acoustics of crepitus and the silent, even insidious start of arthritis, which was visible on an X-ray but not yet causing someone pain.

Crepitus, in other words, suggested that there were problems in the joint, even though it did not ache.

The good news about crepitus, Dr Lo says, is that by indicating that arthritis may be starting, it can allow for early intervention. She says there is "no cure" for knee arthritis, but weight loss and exercise often slow the disease's progression.

And having a creaky knee evaluated by your doctor also can provide peace of mind, she says.

"It's not a universal truth that all popping in the knees is bad," she points out.

Instead, those snaps and pops may indicate only that you are no longer as young as you once were, which is, of course, a universal truth.

NYTIMES