What Is Continuous Passive Motion (CPM)?

What to expect when undergoing this therapy

In This Article

Continuous passive motion (CPM) is a therapy in which a machine is used to move a joint without the patient having to exert any effort. A motor bends the joint back and forth to a set number of degrees, and the amount of movement and speed can be adjusted by the therapist. CPM machines are most commonly used on knee joints (often after knee surgery), but there are versions made for other joints as well.

Purpose of Therapy

Recovering normal joint mobility after surgery can be a significant challenge. The stiffness of a joint can be a complication that limits outcomes and causes pain. Because of this, some surgeons use a CPM to try to prevent scar tissue formation and improve range of motion.

This may be recommended after procedures like ACL reconstruction or frozen shoulder surgery, but CPM is most likely to be prescribed after knee replacement or knee ligament repair surgery. It may also be used after surgery to remove knee tumors in children with osteosarcoma.

In addition to the above benefits, CPM may help reduce the risk of deep venous thrombosis (DVT) after knee surgery. (Compression devices or stockings are also often used to prevent this complication.)

Alternatives to using CPM include physical therapy, active mobilization, and joint manipulation under anesthesia.

Risks and Contraindications

While the use of CPM after knee surgery is common, it remains controversial as to whether the benefits outweigh the risks for many people.

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. But many point to prior reviews that did not find clinically important effects. These include a 2014 Cochrane review of 62 studies.

One study found that CPM was less effective in people who were obese who had total knee replacements. They had poorer self-reported function after six months than those who were not obese.

The American Physical Therapy Association recommends against using CPM after uncomplicated total knee arthroplasty unless the person is unable to participate in active physical therapy and early mobilization. The reasons are that it involves bed rest (which is inconvenient, raises risks of DVT, and can have financial implications) and does not encourage active participation in rehabilitation.

One of the benefits of bending your own joint is not only are you making gains in terms of mobility, but you are also engaging muscles around the joint that require rehab.

Research is ongoing. It is worth discussing your specific case with your healthcare team to determine if CPM is a good idea for you.

Before the Therapy

Before your surgery, talk with your surgical team about what recovery and rehabilitation will entail. Ask what type of mobilization will be done after surgery and when it will begin, and discuss what factors may lead to using CPM rather than active mobilization.

Timing and Location

The use of CPM may begin in the recovery room after surgery or on the day after surgery. Use of the CPM machine may be continuous while you are in the hospital, other than at times when you are receiving other physical therapy or are getting out of bed to use the restroom.

After discharge, the use of CPM may continue at home. Depending on the joint, it may be used for most of the day or for just an hour at a time. Use may continue for several weeks.

Cost and Health Insurance

When a surgery is medically indicated, CPM therapy may 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.

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

Some insurers may cover CPM for some types of surgery (especially knee surgeries) and not for others, in which they consider its use experimental. For example, Aetna does not cover it following back surgery, foot surgery, hip arthroscopy or replacement, shoulder surgery, lymphedema after breast cancer, temporomandibular joint repair, surgical release of elbow contractures, and some other procedures.

During the Therapy

Your physical therapist should inform you about what to expect.

For a knee CPM machine, you place your knee on the supporting frame and fit your foot into the foot pad. Your leg is then secured to the machine with straps. The angle and speed used are determined by your doctor and physical therapist. You may feel pain after your procedure and are likely to be under pain medication, which will be kept in mind.

The CPM machine is used to the limits of your tolerance, so inform your physical therapist when it is too uncomfortable, but aim to use it at the highest angle you can stand.

After the Therapy

You will receive 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 ever uncertain or experience pain, speak with your healthcare team.

CPM is most often used in addition to other physical therapy modalities. Your physical therapist will assess your progress and determine what types of exercises, activities, and other treatments are best for your rehabilitation.

Follow-Up

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

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Article Sources

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