Short answerNo. These machines bend the knee for you in hospital. They made little difference to knee bend, pain or function.
Probably does not help
What it is
A continuous passive motion machine, or CPM, is a frame that moves the knee through a set range, over and over, without any effort from you. It is often used in hospital after a knee replacement to help the knee to bend and to prevent stiffness.
What the research shows
found 24 randomised trials with 1,445 people who had a knee replacement for arthritis. At six weeks, people who used a machine could bend the knee about 2 degrees further than those who did not, with a range from 0 to 5 degrees. Pain was about 0.4 points lower on a 10 point scale, with a range from 0.8 points lower to 0.1 points higher. At six months, function and quality of life were much the same.
Fewer people who used a machine needed the knee to be moved under anaesthetic, about 25 fewer in every 1,000, but the evidence for this was uncertain. The rate of side effects was similar, 15 in 100 with a machine and 16 in 100 without. The reviewers concluded that the machines have no clinically important effects to justify routine use.
Risks and effort
The machine itself carries little risk. The review found a similar rate of side effects with and without it.
What usually works instead
Active exercises, with guidance from a physiotherapist, are the standard approach. See Does physiotherapy help after knee replacement? and Total Knee Replacement.
Questions people ask
Will I get a stiff knee without one?
The review found no important gain in knee bend from using one.
Does it reduce the need for a manipulation?
The review found fewer manipulations in the machine group, but it was uncertain about this result.
Is it harmful?
The review found a similar rate of side effects with and without a machine.
Sources
Select a source to read what the study or guideline found, in plain words, with a link to the original.
Last reviewed 24 October 2026. Next review due October 2028.
