What Is Continuous Passive Motion (CPM)?

Continuous passive motion (CPM) is a therapy that uses a machine to move a joint for a patient. CPM machines are most commonly used on the knee joints, usually after knee surgery. There are also CPM machines made for other joints.

During CPM, a motorized device gently bends the joint back and forth to a set number of degrees. The amount of movement and speed can be adjusted by the physical therapist (PT). 

This article will go over what CPM is and how it's used. You'll also learn what to expect from CPM and what to know about follow-up after treatment.

Purpose of Therapy

Recovering normal joint mobility after surgery can be a challenge. The stiffness of a joint can cause pain and make recovery more difficult. Some surgeons suggest using CPM to help prevent scar tissue formation and improve the range of motion.

CPM is most likely to be prescribed after knee replacement or knee cartilage repair surgery. It might be recommended after procedures like ACL reconstruction or frozen shoulder surgery, as well as after surgery to remove knee tumors in children with osteosarcoma.

A blood clot—also called deep venous thrombosis (DVT)—is a risk after knee surgery. Early joint movement lowers the risk of DVT, but more research is needed to determine whether the use of a CPM is a factor in decreasing this risk. Compression devices or stockings are also often used to prevent blood clots after surgery.

Alternatives to using CPM include physical therapy and active mobilization.

Risks and Contraindications

While the use of CPM after knee surgery is common, research hasn't made it clear whether the benefits outweigh the risks.

A 2019 review of 77 studies involving knee arthroplasty in patients with arthritis found that more intensive CPM (early use and greater flexion) was associated with better short-term and long-term outcomes.

However, many experts point to prior reviews that did not find clinically important effects of CPM.

Some patients might be less likely to get the benefits of CPM than others. For example, a 2017 study found that CPM was less effective in people with obesity who had total knee replacements. The patients' self-reported function was worse after six months than people who did not have obesity.

The American Physical Therapy Association recommends against using CPM after uncomplicated total knee arthroplasty unless you're unable to participate in active physical therapy and early mobilization. That's because it involves bed rest and doesn't encourage active participation in rehabilitation. Benefits of bending your own joint are making gains in mobility as well as engaging muscles around the joint that require strengthening.

As research is ongoing, it's a good idea to talk with your healthcare team about whether CPM is the right option for you.

Before Therapy

Before your surgery, talk with your surgical team about what the recovery and rehabilitation will be like. Ask what type of mobilization will be done after surgery and when it will start, and discuss why you might be prescribed CPM rather than active mobilization.

Timing and Location

The use of CPM may start in the recovery room after surgery or on the day after surgery. Use of the CPM machine can be continuous while you are in the hospital, except for times when you are having other physical therapy or are getting out of bed to use the restroom.

After you go home, the use of CPM may continue. Depending on the joint, it can be used for most of the day or for just an hour at a time. You may continue to do CPM at home for several weeks.

Cost and Health Insurance

If surgery is necessary, CPM therapy might be covered by your health insurance. The charge for in-patient therapy will be lumped in with the cost of the surgical procedure and hospital stay.

If a CPM machine is prescribed for use at home, it may or may not be covered by your health insurance. Under Medicare Part B, CPM is covered for knee replacement surgery for up to 21 days of use at home. Under Original Medicare, you'll pay 20% of the approved amount and the Part B deductible applies.

Some insurers may cover CPM for certain types of surgery (especially knee surgeries) but not for others (for example, if they consider its use to be experimental).

For example, Aetna does not cover CPM after back surgery, foot surgery, hip arthroscopy or replacement, shoulder surgery, lymphedema after breast cancer, temporomandibular joint repair, surgical release of elbow contractures, or other procedures.

During Therapy

Your physical therapist (PT) will talk to you about what to expect during CPM therapy.

If a knee CPM machine is used, you will place your knee on the supporting frame and fit your foot into the footpad.

Then, your leg is secured to the machine with straps. The angle and speed used are determined by your provider and PT.

You may feel pain after the procedure and will probably be given some pain medication if needed.

After Therapy

You will get instructions for using the CPM machine at home. This will include the number of hours to use it per day and whether the settings should be increased each day. If you are unsure about how to use it or have pain, let your healthcare team know.

CPM is most often used in addition to other physical therapy treatments. Your PT will assess your progress and determine what exercises, activities, and other treatments will be best for your rehabilitation.

Follow-Up

At regularly scheduled appointments, your PT will measure the mobility and range of motion of the joint and track your progress. Other forms of rehabilitation or further treatment, if needed, can be discussed during these appointments.

Summary

Your provider may recommend that you do continuous passive motion (CPM) therapy to help you recover from surgery. This type of treatment may help prevent scar tissue and help you get moving sooner.

You’ll learn to use the machine with a physical therapist and may even have a device you can use on your own at home. Your therapist will measure your progress and track your range of motion and flexibility. 

Your insurance may cover the cost of CPM, but only for certain surgeries or for a certain amount of time. Check with your provider before you start treatment to find out what they’ll cover.