How Does It Work?
The limb rests in a padded cradle and a motor moves the joint between two angles you and the therapist set. You do nothing. This matters in the first days after knee or elbow surgery, when pain and muscle inhibition make active movement difficult but a joint left still will begin to stiffen quickly.
The intent is to preserve the range that already exists rather than to force new range. Range settings are increased gradually as tolerance improves, and the device is used for defined periods rather than left running indefinitely.
Passive motion appears to help maintain joint nutrition, since cartilage relies on movement to circulate joint fluid, and it discourages the adhesions that form when a joint stays still. What it does not do is build strength, because no muscle work is involved.
For that reason CPM is always an adjunct. Active exercise, quadriceps activation and progressive loading are what restore function, and CPM simply protects range while you are not yet able to do them properly.
Types/Variations We Offer
Knee CPM: the most common application, used after knee replacement and after some ligament procedures.
Elbow and shoulder CPM: used after stiffness-prone upper limb surgery and prolonged immobilisation.
Progressive-range protocols: start and end angles are advanced daily according to your tolerance.
Short-interval use: several shorter sessions across the day rather than one long one, usually better tolerated.
Conditions Treated
Advantages & Expected Benefits
Maintains joint movement in the days when active exercise is hardest
Requires no effort, so it works when pain and inhibition are at their peak
Range settings are precise and progressed deliberately rather than guessed
Can be used in several short sessions across a day
Discourages the adhesions that follow a joint being kept still
Potential Risks & Short-term Side Effects
Increased pain or swelling if the range is advanced faster than the joint tolerates
Skin pressure or rubbing where the limb rests, particularly over bony points
Nerve irritation from prolonged positioning in one posture
Over-reliance on the device at the expense of the active exercise that actually rebuilds strength
Contra-Indications / Precautions
This treatment may not be suitable for individuals with:
- •Any range or protocol that conflicts with your surgeon specific post-operative instructions
- •Unstable fracture or fixation not yet cleared for movement
- •Active joint infection or an unhealed, discharging surgical wound in the treated area
- •Known or suspected deep vein thrombosis in the limb
- •Areas of significantly reduced sensation, unless supervised throughout
- •Uncontrolled pain that does not settle when the range is reduced
What to Expect in a Session
Surgical clearance: your operation notes and your surgeon range restrictions are confirmed before the device is set up, and they take precedence.
Setup: the limb is positioned and padded, and start and end angles are set within the cleared range.
Supervised run: the first session is supervised throughout so speed and range can be adjusted to your comfort.
Progression: angles are advanced day by day according to tolerance, not to a fixed timetable.
Active work: CPM is always paired with active exercises in the same session, because passive movement alone does not restore strength.
Evidence & Clinical Guidelines
The evidence for CPM after knee replacement is mixed. Reviews have generally found small short-term gains in range that diminish over the following months, with no consistent long-term functional advantage over active exercise alone.
This is stated plainly because it shapes how the device is used here: as a short-term aid during the painful early phase, not as a routine part of every rehabilitation programme.
Where a patient can move the joint actively and comfortably, active exercise is preferred, since it maintains range and builds strength at the same time.
Frequently Asked Questions
Does CPM replace my exercises?
No, and this is the most important point. CPM maintains movement but builds no strength, because your muscles are doing nothing. The active exercises are what restore function, and CPM simply buys range while those are still too difficult.
How long should I use it each day?
Usually several shorter sessions rather than one long one, guided by your tolerance and your surgeon instructions. Longer is not automatically better, and prolonged single sessions tend to cause pressure discomfort.
Is it painful?
It should not be. It should feel like a slow stretch at the end of range, not a sharp pain. If it hurts, the range is set too far and it is reduced. Pushing through pain here causes swelling and sets recovery back.
Will I need one at home?
Sometimes, for a limited period after surgery. If so, you are given written angle settings, session durations and clear instructions on progressing the range, plus what to do if pain or swelling increases.
Need More Information?
Our expert physiotherapists are here to answer any questions you may have about Continuous Passive-Motion (CPM) Devices.
Medically Reviewed
This content was reviewed for medical accuracy by Dr. Surabhi Bansal, BPT, MPT (Ortho) with 14+ years of clinical experience.
At Modern Physio, all medical content undergoes a thorough review process to ensure accuracy and alignment with current physiotherapy standards. Our content is created to educate and should not replace professional medical advice. Learn more about our review process.