CPM Machine: What You Need to Know

CPM Machine: What You Need to Know

You dream of the day when you wake up, swing your legs over the side of your bed and stand without any knee pain. You feel like you're 25 again. These are the dreams of people who deal with knee pain daily and hope for relief with knee surgery.

As you research knee surgery and recovery, you may wonder, do I need a continuous passive motion machine after surgery? A CPM machine will help you regain confidence and mobility quickly as it keeps your leg moving after extensive knee surgery like knee replacement and ACL repair. 

What Is a CPM Machine?


A continuous passive motion machine is commonly known as a CPM machine. It is a machine that keeps your leg moving continuously after you've had knee surgery. 

Your biggest risk after having surgery on a major joint in your body is joint stiffness. You want to regain full knee mobility as soon as possible after knee surgery, but pushing yourself to bend the joint is painful. 

A CPM improves the motion of your knee joint following knee replacement surgery and other knee procedures. It greatly reduces and sometimes even eliminates stiffness. It reduces the chance of scar tissue developing and hindering mobility. 

The machine looks pretty simple. It almost looks like a knee brace in a bent-knee position. You strap your leg into the machine as you lie on you back, and then the machine does the work of moving your leg continuously, straightening and bending the joint.


CPM machines are especially helpful with these cases:

  1. After total knee replacement surgery or after rotator cuff repair. You can use a CPM on your shoulder as well. 
  2. After a surgeon has excised scar tissue from your knee joint because of stiffness
  3. If you have osteoarthritis
  4. After a fracture in your leg

What Does a CPM Machine Do?

In short, a CPM machine keeps your knee pliable and your leg moving. Your doctor may encourage you to use a CPM machine in coordination with physical therapy after knee replacement surgery. Do not replace physical therapy with the CPM machine. 

A CPM machine can help you in a few different ways: 

  • You can regain stronger muscles more quickly. 

You can lose up to 30 percent of your muscle mass if you stay inactive for the first two weeks after surgery. A CPM machine will help you regain muscle mass by moving your leg for you. 

  • You can increase your range of motion in your leg. 

Your joint will feel stiff after surgery, and you won't want to voluntarily bend your leg. The CPM machine will do the work for you, keeping it moving even as you rest. The increased range of motion will prevent scar tissue from forming and decrease pain and stiffness in your knee. 

  • The CPM machine could lead to less pain. 

Initially, you may think keeping your leg moving after surgery would cause more pain. However, the CPM machine keeps your leg elevated, and thus it decreases swelling. With less swelling comes less pain

  • The CPM increases blood flow to your leg. 

The CPM keeps your leg moving and keeps it elevated. This increases blood flow to your leg. With increased blood flow comes quicker healing. 

Should You Use a CPM Machine After ACL surgery?

You may use a CPM machine after ACL surgery. With ACL surgery, your surgeon puts a grafted ligament to repair a torn anterior cruciating ligament that you've torn through injury or accident. Your graft will stretch with the movement of your leg, so a CPM machine should not injure your knee. 

After ACL surgery, your doctor will want you to wear a brace that keeps your leg somewhat immobilized when you walk. When you use the CPM machine, you will want to unlock the brace but keep it on for the first two weeks that you use the machine. 

The proper mixture of physical therapy, CPM machine usage, and cold therapy will help your ACL repair and recovery go smoothly. 

Do CPM Machines Really Work?

Like any tool, the CPM machine can really work if used properly. At one point in orthopedic history, doctors viewed it as an essential part of recovery. 

Studies are showing the CPM machine benefits a patient within the first few days and weeks following surgery. In the long run, though, they're not seeing a difference in knee motion between those who used a CPM and those who did not. 

The Good of a CPM Machine

Proponents of a CPM machine argue that patients experience increased motion after surgery more quickly than those who do not use the CPM machine. 

One of the worst things a patient can experience after having knee replacement surgery is knee manipulation. With this procedure, the patient goes under general anesthesia, and doctors then force the knee to bend. The patient goes under anesthesia because the procedure is so painful. 

When a patient comes out of knee surgery, they want to see growth and improvement right away. A CPM can offer them that improvement and encouragement from start. So even though they're recovering from surgery, resting in bed, their leg is moving, which gives the patient the sense that he or she is recovering more quickly. 

CPM also helps with releasing contracture or adhesions caused by the surgery. It has a good place after knee surgery. 

The Downside of a CPM Machine

In the long run, no one has yet proven that CPM machines make a difference. Within 4 to 6 weeks of knee replacement surgeries, both patients with the CPM machine and those without exhibit the same range of knee motion. So physically, the CPM hasn't proven it makes a difference in long-term recovery. 

Some doctors will even argue that the CPM slows down recovery because a patient needs to lie in bed for it to work. Patients who do not use the CPM machine are more active, sitting up in bed and attempting to move around more. Doctors argue that patients do not get enough effective active therapy because they're still lying down in bed. 

Ultimately, when you consider the effectiveness of a CPM machine, you need to consider the mind-body connection. Will a CPM machine helps a patient believe he or she is recovering more quickly, and then what does that mindset do for the overall wellness of the patient?

How Do You Use a CPM Machine?

A CPM machine is relatively easy to use. A healthcare provider or healthcare equipment representative will show you how to set up your machine. 

You can rent a machine from your healthcare provider, so you can use the machine at home. You do not have to relegate yourself to using it just at the hospital immediately after surgery. 

Your healthcare representative should show you how to adjust the flexion, speed, and time of the machine as well and give you some parameters on what you can expect as you recover. 

Plan on using your CPM machine up to 2 hours at a time for 3 to 4 times a day. Recovery from knee surgery is a full-time job. You can ensure the machine's effectiveness by following these steps: 

  1. Place the machine against a heavy object or your headboard if you plan on using the machine in bed. You need a sturdy surface to keep the machine from moving. 
  2. Plug the machine in. Make sure you keep the cord out of the way so you do not trip over it. 
  3. Remove or adjust your knee brace before you use the machine. Your doctor or healthcare representative should show you how to do this. 
  4. Place your knee in the machine so that the middle of your knee is where the CPM machine bends and your foot is against the footpad. 
  5. Wrap the machine's straps around your foot, shin, and thigh. 

Then turn the machine on and put your recovery time in. You will want to adjust the machine as you recover so you can see more range of motion and improvement. Your healthcare provider should give you these parameters. 

How Often Should I Use a CPM Machine?

Initially, you will use your CPM machine three to four times a day for two-hour increments. You should plan on spending the bulk of your day in the machine, recovering from surgery. 

Before you use your machine, control your pain. Stay on top of your pain by taking appropriate doses of pain medicine 20 to 30 minutes before you use your machine. 

Pain control will help you tolerate the discomfort of the machine more and help you recover more quickly. 

Make sure you keep your machine and its cord out of the way. You do not want to find yourself back in the hospital because you tripped over the machine that should have helped you recover. 

Refrain from smoking around a CPM machine. When you use your CPM machine near an open flame or heat, you could start a fire. 

Water and cleaners can cause damage to a CPM machine, so keep the machine dry. Ask the healthcare representative or provider on how to keep the CPM machine clean. 

When Should I Stop Using a CPM machine?

Do not stop using the CPM machine before your healthcare provider tells you to do so. Depending on the severity of your injury and repair, you may have to use the machine for up to six weeks. 

With that said, if you develop complications, stop using the machine immediately and call your doctor. Watch out for these complications: 

  • A leg that feels warm, tender, and painful. 
  • Fever or chills
  • A red, swollen wound that is draining pus
  • Increased pain while using the machine
  • Stitches that come apart

What is a CPM Machine Rental Cost?

Unless you plan on needing a CPM machine for multiple people in your home, do not buy one. They cost over $2,000. You can rent a machine for 3 to 8 weeks of usage for anywhere from $375 to $550. 

Is a CPM Machine Covered by Insurance?

Yes, insurance may cover a CPM machine. Check your policy. 

Medicare covers CPM machine rental. Part B will cover CPM machines as durable medical equipment if your doctor prescribes its use in your home and if you meet specific conditions. 

If you have knee replacement surgery, Medicare will cover a CPM machine for up to 21 days in your home. 

Make sure your doctors and durable medical equipment (DME) suppliers are enrolled in Medicare. Otherwise, Medicare will not pay the claim your doctor attempts to submit them. 

Ask your medical equipment supplies if they participate in Medicare before you attempt to rent a CPM machine or any DME. If the suppliers participate, they have to accept whatever assignment your doctor prescribes. 

However, if the supplier is enrolled in Medicare but does not "participate," they have the option of not accepting the assignment. In that case, the supplier has no limit one what it can charge you. 

Many insurance providers will cover a CPM machine use at home. For example, BlueCross BlueShield of North Carolina covers a CPM machine at home with specific requirements. For this company and many others, you need these requirements: 

  • It must be medically necessary. Your doctor needs to make this distinction. 
  • If you fall under the condition of "low postoperative mobility or liability to comply with rehabilitation exercises" following total knee replacement or surgery. If you cannot move your knee after surgery without the machine or if you cannot do what your physical therapist asks you to do, you need the machine and qualify for coverage. 
  • If you have extensive arthrofibrosis or tendon fibrosis or have the inability physically, mentally, or behaviorally to participate in physical therapy. 
  • It qualifies only during the time that your knee is healing and you cannot bear any weight on that leg. 

Sit Back and Recover

A CPM machine has proven itself to be an integral part of a patient's recovery from knee surgery. When you use a continuous passive motion machine, even with a knee brace, you improve the range of motion more quickly and boost the patient's confidence in the recovery process. 

If you're suffering from a knee injury and are looking for the perfect solution, contact us. We'd love to help you regain mobility and enjoy life to its fullest. 


  • Nabil

    I need to buy CPM machine for legs and delivery to Libya

  • Ron Rowland

    How about hip replacement?

  • Soniya

    Is CPM machine suitable for dialysis patient and diabetic who have poor leg circulation

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