Dear Dr. Roach: Many years ago, I drove a friend to visit her husband in the hospital. He was 80 and had taken a fall in their yard (no broken bones). When we got there, he was sitting upright in bed, his legs extended with his ankles resting in the cushioned cuffs of a small machine that was about the size of a foot massager. As I remember it, the cushioned part rocked from side-to-side, lifting first one leg and then the other a few inches. The object was to keep the blood circulating in the legs.

I am now 77 myself, with wonky knees, and I think I could use such a machine while resting my legs on an ottoman. I’ve searched online but cannot find one. What I did find was a similar machine that moves from side to side in a fishtailing motion. Am I misremembering what I saw? Would this machine have the same effect on circulation, or would the swishing movement exacerbate the osteoarthritis in my knees? — S.G.

Answer: The intermittent pressure device you saw years ago is a way to try to prevent blood clots from forming in the legs, especially in people at high risk who are unable to walk. It is not as effective as medication. It is used in people who cannot tolerate an anticoagulant, such as people who have had a major bleed.

These devices do not help arterial circulation, nor would they help or hurt your knee.