Knee "buckling" is common, arthritis or not

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NEW YORK, Oct 16 (Reuters) Many middle-aged and older adults have problems with their knee ''go outing'' or ''giving way'' while walking or climbing stairs, even when they don't have knee arthritis, according to a study published Monday.

Researchers found that among more than 2,300 adults ages 36 to 94, 12 per cent said they'd suffered knee buckling at least once in the past three months. The problem was more common in people with x-ray evidence of knee arthritis, but more than half of study participants with knee buckling had no signs of arthritis on x-ray.

The findings are published in the Annals of Internal Medicine.

Knee buckling is a significant problem for two reasons, according to Dr. David T. Felson, the study's lead author and a professor of medicine at Boston University School of Medicine.

''First of all, it causes falls and fractures,'' Felson told Reuters Health. In his study, 13 per cent of people who reported knee buckling in the past three months said it had caused them to fall.

''It's also strongly associated with functional limitations,'' Felson said, explaining that when people know they have a vulnerable knee they tend to avoid activities that could make the joint ''go out.'' Half of study participants with knee buckling said they were limited, at least somewhat, in their daily activities.

Knee arthritis certainly plays a role in knee buckling, Felson said, as does knee pain in general, whatever the source. Buckling was ''far more common,'' he and his colleagues report, among people with knee pain compared with their pain-free counterparts.

Felson explained that chronic pain and inflammation inhibit contraction of the quadriceps, the muscles at the front of the thigh. This, in turn, can destabilize the knee joint.

When he and his colleagues examined the factors that seem to put people at particular risk of knee buckling, quadriceps weakness turned out to be one.

This implies that exercises to strengthen the quadriceps could help prevent knee buckling, according to Felson. ''We don't know this for sure, since this wasn't a trial studying that,'' he noted, ''but it would make sense that strengthening is a reasonable thing to have these patients do.'' The findings also suggest a reason for the heightened rate of bone fractures among people with knee arthritis, according to Felson. This risk has been puzzling given that, as a group, people with knee arthritis are relatively heavier and have greater bone density -- factors that should lower their fracture risk.

Knee buckling, and subsequent falls, may explain the fracture risk associated with knee arthritis, Felson explained. He noted that it's not common practice for doctors to ask knee arthritis patients whether they have problems with buckling; his group's findings, he added, suggest that they should.

Reuters SS DB0917

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