Continuous Passive Motion Therapy (Do CPM Machines Work?)

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Continuous Passive Motion (CPM) can be a therapy used as part of recovery after knee replacement surgery.

Although I didn’t use one during my recovery, I know they can be a valuable component for other people’s rehabilitation. I will outline how it works specific to the knee joint and discuss some of the pros and cons of continuous passive motion machines (or CPM machines).

This is not a therapy that you should choose on your own. The decision to use a CPM machine should be made by your surgeon or your physical therapist.

There are alternatives to CPM which include physical therapy and active manipulation. I’ll share how I recovered and I’ll provide helpful information for your recovery.

What Is A CPM Machine?

A Continuous Passive Motion Machine is a post-surgical therapy that is used to move the joint without the patient exerting any effort. The machine is motorized and bends the knee joint back and forth.

Your therapist is able to adjust the machine to a specific number of degrees and can also set the machine at the desired speed. CPM machines are most commonly used on knee joints after surgery but there are machines made for other joints too.

The machine is normally used during the initial healing period, immediately after knee replacement surgery and the first few days of recovery.

Purpose of Continuous Passive Motion Therapy

After knee replacement surgery, your medical team will want you to begin walking and working on your range of motion.

The CPM machine helps to keep your knee moving right after surgery, while you are still in your hospital bed. The CPM machine moves the knee joint without your help.

Some surgeons have recommended CPM machines to prevent scar tissue (learn how I massaged my scar) from forming that may result in stiffness. Scar tissue in and around the joint could limit your range of motion.

Stiffness in your knee joint can cause complications that may cause pain and lead to a required “knee manipulation” under anesthesia by your surgeon.

How the CPM Machine Works

The CPM machine can work if you are lying down or sitting up. You place your knee on the frame of the CPM knee machine.

Your foot fits into a footpad that is adjustable. Your leg is secured by adjusting the straps (which are attached to the machine). The physical therapist or your doctor can adjust the speed and angle of the machine.

The CPM machine can be adjusted to how much pain you can tolerate. Pain is a part of the recovery process, including the CPM machine. Medication if prescribed will certainly help.

Pros and Cons of Using a CPM Machine

As I have mentioned in other articles, everyone has a different experience with recovery. While some medical professionals will recommend using a CPM machine, others may be against it.

It all comes down to your specific situation and needs. From my surgery, I learned that movement of the joint immediately was essential for my recovery.


  • It may help the range of motion in your knee increase.
  • Promotes blood circulation.
  • It is a passive motion and no effort is required of the patient.
  • Some patients with other health issues might not be able to do the physical exercise necessary to rehab the knee using their own effort.
  • There could be a psychological benefit seeing your knee bending immediately after TKR surgery.
  • The CPM machine elevates your leg which can decrease swelling. This may also help pain caused from swelling.
  • It may help prevent scar tissue from building up.


  • Many doctors no longer recommend CPM machines because newer research does not support their use. According to my reading, studies do not show a significant difference in TKR patients using the CPM machine. The studies I read indicate that patients are likely to be at the same point of recovery within several weeks of surgery regardless of the use of the CPM machine. My doctor did not think the CPM machine was necessary for my post-surgery recovery. He prescribed active physical therapy from day one.
  • When patients rely on the machine too much it sometimes keeps them in bed longer.
  • The machine might not be comfortable and you may have trouble napping or sleeping when it is in use.
  • Cost can be an issue. Most insurance companies pay for the in-hospital use of the CPM machine. Not all cover the cost of renting a CPM machine to use at home. My research on the internet indicates that most machines cost over $2,000.00.
  • Doctors who do not recommend the machine prefer to have their patients up and focusing on active therapy.

Options for CPM (and similar products)

The Vinmax CPM machine (click to view on Amazon) is one of a few options available on Amazon. It uses a motor and digital display to keep the knee joint moving without the help of your muscles.


  • Adjustable straps
  • Adjustable angle and speed
  • Digital display
  • Motor – self-moving

The user can change the angle and speed of the CPM to suit their needs. One of the cons of this piece of equipment is the price (it’s not very affordable).

The Knee Glide (view on Amazon) is another option to keep the knee joint moving. It is not a traditional CPM machine because it requires the user to manually move the legs (no motor).

However, it is more affordable and has superb reviews. It is portable and can be used while seated or standing. I really like this option compared to the motorized version mentioned above.

Alternative to a Continuous Passive Motion Machine

Most surgeons seem to prefer that their TKR patients engage in active physical therapy immediately after surgery if their health permits. For me, active therapy started in the hospital about 4 hours after my surgery.

A physical therapist came to my room and gave me simple exercises that I could do in bed and she encouraged me to begin walking with a hospital-provided walker.

Initially, I started with simple ankle pumps and ankle rotations (these exercises are easy and worked great). I was encouraged to walk with the walker to and from the bathroom.

On day two my therapist took me on a walk down the hall with the walker, and later returned for a longer walk to her exercise room where she gave me a stair test that I had to do before being discharged (read more about my post-surgery exercise routine).

Once at home, I was visited by a home physical therapist 3 times a week for a total of 12 visits. She gave me a strenuous set of exercises that I was to do 3 times a day.

It was much easier doing the set with her watching and encouraging. Doing the exercises on my own took a good deal of self-discipline.

Sometimes the pain seemed unbearable but I made myself complete the exercises. Not easy! Thankfully, my extension returned without much effort. The flexion was the real test for me.

The two most helpful and painful exercises were ankle slides’. The first, lying flat on my bed and pulling my ankle back towards my butt using a robe belt to pull.

The second most beneficial exercise was sitting in a chair, sliding my leg as far back under the chair as I could using a plastic bag to slide on the tile floor. After 10 reps, I wrapped my good ankle around the front of my surgical leg and forced it back as far as I could for another 5 reps.

I did both of these 2 exercises 3 times a day, three sets of 15 along with several other exercises she prescribed. See my other articles for specifics.

The stationary bike in the fitness center was another great tool for increasing my flexion. You can adjust the resistance and increase the time whenever you desire. I prefer to ride a regular bike but it is a good substitute until you feel comfortable enough to get back on the road.

I was also encouraged to begin massaging my knee around the scar as close as I could get using “Free Up” lotion (read my article about Free Up and other medicine I used). As I healed, I continued to massage the entire knee even the scar itself.

As soon as I was given the okay to resume swimming I was back in the pool. Flexing and bending the knee in the water was easier with little resistance.

I also began using the hot-tub when I got the okay and the heat and jets helped with flexion and bending.


Knee range of motion (ROM), as well as a reduction in pain, is considered to be one of the primary indicators of a successful TKR. 

Most surgeons have opted not to use CPM machines. Instead they prescribe active physical therapy for their patients. There is quite a bit of research now supporting physical therapy intervention for improving knee range of motion and function following TKR surgery.

A CPM machine might be appropriate for patients who have underlying health issues, especially those who have trouble walking after surgery. Remember, everyone is different. Consult your medical team and physical therapist to find out what is best for you.