CPM in physiotherapy stands for Continuous Passive Motion, a motorised device that gently bends and straightens a joint through a set range of motion while the patient stays completely relaxed and uses no muscle effort. Continuous Passive Motion is used mainly in the first days and weeks after joint surgery, most often knee replacement, to keep the joint moving before a patient can move it on their own. This article covers what the machine does, how it works, which joints it fits, when it is started and for how long, how to use it safely at home, why routine use has declined in recent years, what has replaced it, and how coverage works in Ontario.

What Is CPM in Physiotherapy?

CPM in physiotherapy is Continuous Passive Motion, a rehabilitation technique where a motorised device moves a joint passively and repetitively through a specified range while the patient contributes no active effort. Physiopedia describes it as machine-assisted regular movement applied at an early stage of rehabilitation, typically after joint surgery. Joint surgery leaves a patient unable to bend or straighten the limb under their own power for several days, and that gap is the problem Continuous Passive Motion was designed to fill.

Filling that gap matters because a joint left still after surgery does not simply wait. St. Jude Children’s Research Hospital explains that range of motion can become permanently limited when scar tissue forms, or when swelling and stiffness set in while the joint heals. Healing with the joint immobile produces a stiffer result than healing with the joint moving, which is the single idea the whole technique rests on.

What Does CPM Stand For in Physiotherapy?

CPM stands for Continuous Passive Motion, sometimes written as continuous passive movement. The word passive carries the meaning: the machine performs the movement and the muscles stay switched off. Switched-off muscles are the point rather than a limitation, since a joint repaired a day earlier cannot safely be loaded by the muscles that cross it.

What Joints Can a CPM Machine Be Used On?

A CPM machine can be used on the knee, hip, shoulder, elbow, ankle, and wrist, with the knee by far the most common application. Physiopedia and St. Jude Children’s Research Hospital both list that same set of joints, and each device is purpose-built for one joint rather than adjustable between them. Building a device for one joint allows the cradle to match the limb shape and the motor arc to match the joint’s natural movement. Natural movement is what the machine reproduces, and understanding how it does that explains both its strengths and its limits.

How Does a CPM Machine Work?

A CPM machine works by cradling the limb in a motorised frame that slowly bends and straightens the joint through settings a therapist programs for speed, range, and duration. St. Jude Children’s Research Hospital describes the three components as a frame with a cradle to hold the joint, a motor that moves it, and controls for time, speed, and range of motion. Range of motion settings are usually increased by a small amount each day as healing allows, which turns the device into a slow, measured progression rather than a fixed treatment.

Progression happens entirely without the patient’s participation. The limb is strapped into the cradle, the machine runs, and the patient rests, reads, eats, or sleeps while it works. Working this way means the session feels like someone gently moving the limb for you, with mild stretching or pulling as the normal sensation and sharp pain never being normal. Normal sensation also includes a soft hum from the motor and light pressure from the straps.

What Is the Difference Between Passive and Active Motion?

The difference between passive and active motion is that passive motion moves the joint using an outside force while active motion moves it using the patient’s own muscles. Muscles that contract during active motion gain strength, improve their timing, and relearn control of the joint. Control and strength are precisely what passive motion cannot produce, because a muscle that never contracts never adapts.

Adaptation is the dividing line between a device and a treatment. Continuous Passive Motion maintains the space a joint can move through; active exercise rebuilds the ability to use that space under load. Loading under control is the work that happens in physiotherapy, and it is why every authoritative source describes CPM as an adjunct rather than a treatment in its own right. Its own contribution still matters in the first days, and the mechanism behind that contribution is worth setting out properly.

What Are the Benefits of Continuous Passive Motion?

The benefits of continuous passive motion are reduced joint stiffness, less swelling and pain, lower analgesic use, reduced blood clot risk, and faster early return of joint mobility. Those benefits trace back to a specific healing mechanism. O’Driscoll and Giori, writing in the Journal of Rehabilitation Research and Development, described post-surgical joint stiffness as progressing through four stages: bleeding, oedema, granulation tissue, and fibrosis.

Fibrosis is the stage that produces lasting stiffness, and it arrives last. Bleeding and oedema occupy the first days after surgery, which is the window where passive movement does its work. Passive movement in that window maintains normal periarticular soft tissue compliance and helps pump blood and oedema fluid away from the joint before the tissue begins laying down the fibrous bands that restrict movement permanently. Permanent restriction is also why Physiopedia notes CPM does not interfere with open wounds, nursing care, or external fixation, making it usable at a point when almost nothing else is.

Usable timing aside, the technique sits in a spectrum of movement, and comparing the three types clarifies what each actually delivers. The distinctions below draw on the clinical descriptions published by Physiopedia and St. Jude Children’s Research Hospital.

Type of motion	What moves the joint	What the tissue gains	When it is used	What it cannot do
Continuous passive motion	A motorised device	Maintained range, reduced oedema, less adhesion formation	Days 1 to 14 after surgery, before active movement is possible	Build strength or restore muscle control
Active-assisted motion	The patient’s muscles with help from the other limb, a therapist, or a strap	Early muscle activation plus maintained range	From the first week onward as pain allows	Load the joint enough for full strength gains
Active exercise	The patient’s own muscles against resistance	Strength, control, endurance, functional capacity	From the early weeks through the full rehabilitation programme	Be performed safely in the first days after some surgeries

The middle row explains most of what has changed in post-surgical care over the past decade. Active-assisted movement achieves much of what passive movement achieves while also switching the muscles back on, which is why surgical teams increasingly favour it. Favouring it has not removed Continuous Passive Motion from practice entirely, and where it is used, the swelling effect remains one of its clearest contributions.

Does a CPM Machine Help With Swelling?

A CPM machine does help with swelling, because the continuous repetitive motion pumps blood and oedema fluid away from the healing joint and the surrounding tissue. Surrounding tissue holds fluid easily after surgery, and fluid that sits still contributes to both pain and stiffness. Stiffness from retained fluid responds well to gentle movement, which is also why compression, elevation, and hands-on techniques such as massage therapy are used alongside it in the later weeks. Weeks are the right unit here, because timing determines whether any of this works.

When Do You Start Using a CPM Machine After Surgery?

You start using a CPM machine within the first 24 to 48 hours after surgery, often on the same day, while the joint is still in the bleeding and oedema stages of healing. Starting that early is not a matter of enthusiasm. O’Driscoll and Giori showed that passive movement maintains tissue compliance only during those first two stages, which means a machine introduced in week three has largely missed its window.

Missing the window changes the goal of treatment from prevention to recovery, and recovery of lost range is slower and harder than preventing its loss. Preventing it requires a schedule, and your surgical team or our physiotherapists will set the specific settings based on the procedure performed.

How Long Does CPM Therapy Last?

CPM therapy lasts several weeks in most protocols, with sessions typically running 1 to 2 hours at a time. St. Jude Children’s Research Hospital describes a usual plan of 1 to 2 hours per session, 3 to 4 times each day, continued over several weeks. Several weeks is a general guide rather than a fixed rule, and research has not settled the question. Harvey, Brosseau and Herbert reported in their 2014 Cochrane review that the optimal timing, session length, and total duration of CPM remain genuinely controversial, with short-term use appearing sufficient for short-term range gains.

How Often Should I Use a CPM Machine After Knee Replacement?

You should use a CPM machine after knee replacement 3 to 4 times each day for 1 to 2 hours per session, following the schedule your care team sets. Your care team adjusts that schedule to the procedure, your pre-operative range of motion, and how the joint responds in the first few days. Responding well usually means the range setting increases slightly each day, with the therapist making the adjustment rather than the patient.

Can I Sleep With a CPM Machine On?

You can sleep with a CPM machine on, and St. Jude Children’s Research Hospital notes the device can be used while relaxing, eating, or sleeping. Sleeping through a session is possible because the machine does all the work and requires nothing from the user. The user still needs the straps checked for comfort before a long session, since pressure that is tolerable for twenty minutes can irritate the skin over several hours.

What Range of Motion Should a CPM Be Set To?

A CPM should be set to the range your surgeon or physiotherapist specifies, which usually starts conservatively and increases in small daily increments. Increments are kept small deliberately, because range gained faster than the healing tissue tolerates produces pain, swelling, and a setback rather than progress. Progress across a full course depends on several factors together, and Liao and colleagues reported in Knee Surgery, Sports Traumatology, Arthroscopy that outcomes relate to pre-operative range of motion, the post-operative day CPM begins, the daily range increment, and the total number of sessions.

How to Use a CPM Machine Safely at Home

You use a CPM machine safely at home by following the settings your care team prescribed, checking the skin after every session, and stopping if anything feels sharp rather than mildly stretching. Stretching sensations and mild soreness are expected; sharp pain, numbness, or increasing swelling are not. St. Jude Children’s Research Hospital sets out the following practical sequence for home use.

1. Place the machine on a flat, firm surface before positioning the limb.
2. Keep the controller within reach so settings can be adjusted if you have been instructed to do so.
3. Position your body and place the joint into the cradle exactly as your therapist showed you.
4. Fasten the straps snugly, but never tightly enough to cause pain or pinching.
5. Place a soft cloth between the skin and the straps if the skin is sensitive or the session will be long.
6. Set the machine to the prescribed settings, and do not change them unless instructed.
7. Run the session, staying relaxed and letting the machine do all the movement.
8. Check the skin for redness or irritation after the session ends.
9. Clean the straps, padding, and cradle with a damp cloth or disinfectant wipe, keeping moisture away from the motor.

Step six is the one most often broken. Breaking it by increasing the range yourself feels productive and is the fastest route to an inflamed joint, since the daily increment is calculated against healing tissue rather than against how the joint feels on a good day. A good day is not a reason to double the dose.

Can You Use a CPM Machine Too Much?

You can use a CPM machine too much, and excessive use produces joint irritation, increased swelling, skin breakdown under the straps, and pain that outlasts the session. Sessions that leave pain lingering for hours afterward signal that either the range or the total daily time is too high. Too much time in the machine also carries a less obvious cost: hours spent lying passively are hours not spent on the active movement, walking, and strengthening that actually drive the long-term result.

Who Should Not Use a CPM Machine?

People who should not use a CPM machine include anyone whose tissue, circulation, or awareness cannot safely tolerate repeated passive movement. Physiopedia lists the following contraindications.

• Deep vein thrombosis
• Acute inflammation
• Severe osteoporosis
• Cardiovascular or neuromuscular disease
• Cognitive deficits that prevent reporting pain accurately
• Severe obesity, defined as a body mass index above 35 kg per square metre
• Severe pain
• Spastic disorders
• Bleeding disorders or anticoagulant use

Cognitive deficits sit on that list for the same reason impaired sensation sits on most modality contraindication lists. The patient’s own report of pain is the safety mechanism, and a device that runs for two hours unattended depends entirely on that report. Reporting problems promptly is equally important once treatment is underway.

When to Stop and Call Your Care Team

You should stop using the CPM and contact your care team right away if sharp pain appears, if pain does not improve even after the range setting is reduced, or if swelling increases. Increasing swelling, numbness or tingling, blisters or sores on the skin, redness or warmth or fluid coming from the incision, and a joint that locks up or stops moving normally all warrant a call rather than another session. Another session should also wait if the machine itself develops worn straps, cracks, cord damage, or clicking sounds, in which case it should be unplugged until a therapist checks it. Checking the device and the joint regularly is standard practice, and it is part of why the technique has come under closer scrutiny over the last decade.

Why Are CPM Machines No Longer Used as Routinely?

CPM machines are no longer used as routinely because large reviews have found the range-of-motion gains to be short-term, with no demonstrated long-term functional benefit to justify routine use. Harvey, Brosseau and Herbert reached that conclusion in their 2014 Cochrane review of CPM following total knee arthroplasty. Yang and colleagues reported much the same in a 2019 systematic review and meta-analysis published in Archives of Physical Medicine and Rehabilitation, finding evidence favouring routine use still lacking.

Lacking evidence accumulated further in the years that followed. Gil-González and colleagues reported in the Journal of Orthopaedic Surgery and Research in 2022 that CPM did not affect knee motion or surgical wound appearance after total knee arthroplasty. Appearance and motion were the two outcomes the technique was expected to improve most, and the shift in practice followed. Following that shift, surgical programmes moved toward early mobilisation: getting patients standing and walking within hours of surgery, which produces the circulation and movement benefits while also switching the muscles back on.

Switching muscles back on early also reduced the problems CPM was invented to solve. Modern surgical technique, better pain control, and same-day mobilisation protocols mean fewer patients spend days unable to move the joint at all. At all is the key qualifier, since the technique still has a place where movement genuinely is not possible, and chiropractic care and other hands-on approaches fill different roles further along the same timeline.

Do Doctors Recommend CPM Machines?

Some doctors recommend CPM machines and many no longer do, with practice varying by surgeon, procedure, and country. Country and institution matter more than the individual case in many settings, since protocols are often set at the programme level. Programme-level decisions have moved away from routine use after standard knee replacement, while CPM remains more commonly prescribed after cartilage repair, surgical release of joint contractures, and complex procedures where early active movement is genuinely unsafe. Vasileiadis and colleagues also reported in the American Journal of Physical Medicine and Rehabilitation that CPM may limit the growth of heterotopic ossification, which is one of the specific scenarios where it retains clear support.

Do They Still Use a CPM Machine After Knee Replacement?

They still use a CPM machine after knee replacement in some programmes, though it is no longer standard practice in most. Most centres now rely on early walking, active-assisted knee bending, and supervised rehabilitation starting on the day of surgery. Surgery followed by same-day mobilisation has produced equal or better outcomes in the published comparisons, which is the practical reason the machine appears less often than it did fifteen years ago.

Is a CPM Machine Better Than Physical Therapy?

A CPM machine is not better than physical therapy, and the two are not alternatives to each other. Physiopedia states the position directly: CPM should not be used as a substitute for physiotherapy treatment or as the only intervention in a management plan, because it tends to produce short-term range gains without long-term functional benefit. Functional benefit comes from strength, balance, gait retraining, and graded loading, and none of those can be delivered by a machine that moves a limb while the patient rests.

Resting while a joint moves has its place in week one. By week three the limiting factor is almost never the available range, it is the quadriceps strength needed to climb a stair and the confidence to put weight through the leg. Weight-bearing confidence is rebuilt through progressive loading, which is what a physiotherapy assessment is designed to plan, and you can read more about our clinic and how the team coordinates post-surgical care. Coordinated care usually means our Markham clinic picks up a patient at the point hospital-based treatment ends.

What Can I Use Instead of a CPM Machine?

You can use active-assisted range of motion exercises instead of a CPM machine, including heel slides, seated knee bends using the other leg for assistance, and supported standing knee flexion. Supported movement achieves the same joint motion while recruiting the muscles, which is the advantage the machine lacks. Lacking muscle recruitment is why most programmes now pair those exercises with early walking, ankle pumps for circulation, and a progressive strengthening plan delivered through exercise rehabilitation. Rehabilitation of that kind raises the practical question of what any of it costs.

What a CPM Machine Costs and How Coverage Works in Ontario

A CPM machine is usually rented by the week rather than purchased, and the cost depends on the joint, the rental period, and whether delivery and setup are included. Included services vary considerably between suppliers, and the rental period is normally measured in weeks because the clinical window for the device is short. Short windows make purchase difficult to justify for most patients, which is why rental is the standard route.

Routes to coverage in Ontario depend on how the injury or surgery occurred. Extended health benefit plans sometimes cover durable medical equipment rental with a physician’s prescription, though the specific terms vary by plan and many exclude CPM outright now that routine use has declined. Declining routine use has affected coverage decisions directly, since insurers follow clinical guidelines. Guidelines aside, WSIB claims and motor vehicle accident insurance operate under different rules and often cover equipment and rehabilitation services that a standard benefit plan would not, so the funding route is worth confirming before surgery rather than after. Confirming it early also gives time to arrange the post-surgical physiotherapy that follows, which is the part of recovery that actually determines the result.

Frequently Asked Questions

What Is the Hardest Joint Replacement to Recover From?

The hardest joint replacement to recover from is generally the knee, because the joint depends heavily on muscle control and the quadriceps are substantially weakened by the surgery itself. Hip replacement patients often walk comfortably within weeks, while knee replacement patients commonly need three to six months to regain full function. Function returns fastest for patients who had better range of motion and strength before surgery, which is why pre-operative rehabilitation is increasingly recommended.

What Can You Never Do Again After Total Knee Replacement?

After total knee replacement, most surgeons advise permanently avoiding high-impact activities such as running, jumping, basketball, and singles tennis, because repeated impact shortens the lifespan of the implant. Walking, cycling, swimming, golf, hiking, and doubles tennis are all generally encouraged instead. Kneeling is often uncomfortable rather than unsafe, and many patients regain it partially over the first year.

Does a CPM Machine Hurt?

A CPM machine should not hurt, and the normal sensation is mild stretching or pulling with slight soreness afterward. St. Jude Children’s Research Hospital describes the experience as feeling like someone gently and slowly moving the joint for you, along with light pressure from the straps and a soft hum from the motor. Pain or irritation during or after a session means the settings need adjusting and should be reported to your therapist.

Can a CPM Machine Be Used After ACL Reconstruction?

A CPM machine can be used after ACL reconstruction, and ligament reconstruction appears on the standard indication list alongside joint replacement, open reduction internal fixation of fractures, synovectomy, and release of extra-articular contractures. Use after ACL reconstruction focuses on restoring full extension early, since a knee that cannot straighten fully causes more long-term trouble than one that cannot fully bend. Protocols differ by surgeon and graft type.

How Soon Can You Walk After Knee Replacement?

Most people walk with a frame or crutches within hours of knee replacement surgery, and many take their first supervised steps the same day. Same-day mobilisation has become standard because early weight-bearing improves circulation, reduces blood clot risk, and speeds the return of function. Walking distance builds gradually over the following weeks, with most patients moving off walking aids somewhere between two and six weeks.

The Bottom Line

CPM stands for Continuous Passive Motion, a motorised device that moves a joint through a set range while the patient stays relaxed, used in the first days after joint surgery to limit stiffness, pump away swelling, and maintain the movement a joint would otherwise lose. Losing that movement is prevented only during the bleeding and oedema stages of healing, which is why the machine is started within the first day or two and why a late start achieves far less. Less routine use is now the norm, because the large reviews found the range gains to be short-term and modern protocols get patients moving actively within hours instead.

What has not changed is where the long-term result comes from. Strength, control, balance, and graded loading rebuild a joint’s function, and no device delivers those while the patient rests. If you are preparing for joint surgery or working through recovery and want the active half of that plan properly structured, an assessment at KC Rehab in Markham will map it out, and you are welcome to contact us with questions beforehand.