Glossary
Continuous passive motion (CPM)
Quick answer
Continuous passive motion uses a motorised frame that slowly bends and straightens the knee while you lie relaxed, without your muscles doing the work. It is used selectively after certain operations, explains Dr. Pablo Gelber, knee surgeon at Aman Hospital in Doha, rather than for every patient.
What it is
The leg rests in a padded cradle on a frame that moves the knee through a set range, for example from straight to a chosen angle, at a slow, steady speed. The range is increased gradually as comfort allows. Sessions are usually done in bed for a few hours a day.
The movement is passive: the machine moves the joint, while active exercises, in which you use your own muscles, remain the core of rehabilitation.
Why it matters for patients
Research after routine knee replacement has shown little long-term benefit from CPM compared with good physiotherapy, so it is not used routinely by many surgeons. It may help in specific situations, such as some cartilage repairs where gentle motion nourishes healing tissue, after release of a stiff knee, or when a patient cannot exercise early.
Its main drawback is time in bed, which can take time away from walking and active exercises.
How it is used
If CPM is prescribed, your team sets the range, speed and hours. Stop and report it if pain rises sharply, the wound leaks or the leg slips in the cradle. It does not replace the exercises your physiotherapist gives you.
Frequently asked questions
Will a CPM machine stop my knee getting stiff?
On its own, usually not. Regular active exercise, swelling and pain control, and early walking matter more for avoiding stiffness after most operations.
Can I rent a CPM machine for home use?
Home machines are available in some situations. Whether you need one depends on your operation, so ask your surgeon before arranging one.
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