Knee buckling which is a sudden "giving way" of the knee is not an uncommon event particularly for older people.
Knees often buckle when there is an increase in weight-bearing such as when a person goes up or down stairs.
Although it commonly occurs in people with severe knee arthritis or after knee surgery some experts believe it is also common among adults without these problems.
In order to better understand the problem and to identify factors associated with knee buckling researchers from Boston University School of Medicine conducted a study.
The researchers recruited 2,351 community-dwelling adults, 36 to 94 years of age who had participated in 2 other population-based studies conducted in Framingham, Massachusetts.
None of the participants had rheumatoid arthritis or had undergone knee replacement surgery.
The team questioned the participants about knee buckling in the past 3 months, knee pain and stiffness in the past month and physical function activities related to lower limbs, such as climbing stairs.
They measured the strength of thigh muscles and also took knee x-rays to check for osteoarthritis and sometimes did magnetic resonance imaging (MRI).
They then analysed the data and found that 278 (12%) adults reported at least 1 episode of buckling in the past 3 months; of these, 13% fell during the episode.
The knee buckling occurred just as often among men and women and was more common amongst middle-age and older persons.
Most were walking or climbing stairs when their knees buckled and most people reported more than one episode of buckling.
It was found that knee pain, quadriceps weakness, radiographic osteoarthritis, and limitations of physical function were more common among patients with buckling than among those who reported no buckling.
However over half of those with buckling had no osteoarthritis.
The researchers say knee buckling appears to be common among middle-age and older adults and may cause falls and limit a persons ability to climb stairs.
The study appears in the 16th October 2007 issue of Annals of Internal Medicine (volume 147, pages 534-540).