Benefits of a Continuous Passive Motion (CPM) Machine (2024)

A continuous passive motion machine (also known as a CPM machine) is a motorized device used in physical therapy that gently bends a joint back and forth to aid with recovery following a joint injury or surgery. It is typically designed for the knee, but there are also CPM machines for joints like the hip or shoulder.

The therapy is called passive because you let the machine do the work. The purpose of CPM is to restore the range of motion of a joint to its pre-treatment level and prevent scarring that can result in a loss of joint mobility.

This article will explain what CPM is and what to expect before and after therapy. It will also describe some of the risks of CPM therapy and whether they actually help.

What Does a CPM Machine Do?

A CPM machine is used during the first phase of rehabilitation following joint injury or surgery. The motorized device continually moves a joint through a controlled range of motion. The levels can be increased over time as recovery progresses.

The purpose of CPM therapy is to control post-operative pain, reduce inflammation, improve the range of motion, and ensure that the joint heals properly without scarring or adhesions (the sticking together of tissues).

There are different CPM machines used for people who have undergone or experienced:

• Adhesive capsulitis (frozen shoulder)
• Anterior cruciate ligament (ACL) repair
• Elbow surgery
• Hip replacement surgery
• Knee arthroplasty (knee replacement)
• Knee cartilage repair surgery
  
• Osteosarcoma resection
• Stroke

CPM may also reduce the risk of a potentially dangerous condition called deep venous thrombosis (DVT) following knee surgery.

Do Continuous Passive Motion Machines Help?

CPM therapy appears to be beneficial with certain conditions, although it remains unclear if it is necessarily the "best" option overall. This is because some conditions benefit from a more active approach to rehabilitation, particularly if the individual is in good health.

A 2019 review of 77 studies found that intensive CPM therapy was associated with better short-term and long-term outcomes for people with knee arthritis who underwent knee arthroplasty.

Even so, some people may have less benefit than others. A 2017 study found that CPM was far less effective in people with obesity following total knee replacement compared to those without.

Some experts question whether active mobilization (involving exercises that actively bend and straighten joints) may be better for total knee arthroscopy and ACL tear than CPM. Certain CPM therapies, like those used for elbow injuries, have demonstrated little to no benefit.

The American Physical Therapy Association currently advises against CPM therapy after uncomplicated total knee arthroplasty unless a person is unable to participate in active physical therapy.

Using a CPM Machine

Before surgery, talk with your surgical team about what your rehabilitation and recovery plan will involve. This includes whether passive or active mobilization will be used and why.

Before Therapy

Your surgical team will prepare you in advance if CPM therapy has been prescribed.

CPM therapy may start immediately in the recovery room after surgery or the day after your surgery. The machine may be used continuously while you are in the hospital, except for when you are having other physical therapy or using the restroom.

After you return home, you may be prescribed a home CPM unit to use most of the day or just a few hours a day. At-home therapy may continue for several weeks.

During Therapy

There are different CPM machines for different joints, but they work under the same principles. The units generally conform to the joint that is being treated. Prior to being strapped in, the healthcare provider or physical therapist will set the machine to a designated speed and range of motion.

Once you are strapped in, the machine is turned on and will move the joint repetitively so that it bends and straightens along a controlled plane of movement.

CPM machines for the knee or hip are mobile devices that are placed on a bed and move the joint while you are lying down. If you have a CPM machine for your shoulder or elbow, you'll sit in a specially outfitted chair.

During the procedure, you may feel slight discomfort but should not feel outright pain. If you do, let the provider know so that the speed, range of motion, or position of the unit can be adjusted.

After Therapy

You may feel pain after the procedure and may be given pain medication like Tylenol (acetaminophen) or Advil (ibuprofen) if needed.

If at-home CPM is needed, you will be given instructions on how to use the machine. This includes how many hours to use it per day and whether the settings need to be increased every few days or so. If you are unsure or experience pain, let your healthcare provider know.

CPM is often used with other physical therapies. Your physical therapist will monitor your progress and determine which exercises or treatments are best suited based on your progress.

Follow-Up

At each regularly scheduled appointment, your physical therapist will track your progress by evaluating your range of motion and other functional measures.

This may include a self-assessment survey like the Knee Outcome Survey Activities of Daily Living Scale (KOS-ADLS). The survey includes sixquestions about symptoms during daily activities and eight questions about limitations experienced as the result of knee replacement.

If you are not improving as you should, you may be referred back to your surgeon for imaging studies to check if the repair failed or healed abnormally.

Summary

Your healthcare provider may recommend continuous passive motion (CPM) therapy to help you recover from a joint injury or surgery. The treatment involves a motorized device that moves a joint repetitively at a set speed and range of motion. CPM therapy may start in the hospital and continue at home with a home unit.