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A continuous passive motion (CPM) machine is a motorized device that passively moves a joint through a pre-set range of motion. These devices may be used after surgery to reduce joint stiffness and improve range of motion. They’re sometimes used after knee replacement surgery but can also be used after elbow, hip, or shoulder surgery.

CPMs have traditionally been used in hospitals and as take-home devices. However, research published over the past decade has begun to question their effectiveness.

Keep reading to find out what the latest research says and how you can use CPM when recovering from your surgery.

Joint stiffness after certain types of operations can be a concern. Over time, this may lead to scar tissue buildup and permanently impaired range of motion.

CPM machines move your joint without you having to move your muscles. It’s thought they help by counteracting the negative effects of prolonged immobilization. However, the benefit of CPM use is controversial. Several studies have shown no improvement in range of motion in patients who used them post-operatively.

The American Physical Therapy Association recommends avoiding CPM machines after a total knee replacement. The recommendation came after a number of recent studies found that CPM machines had no benefit for improving recovery.

Some studies do suggest that CPM machines may be beneficial in some situations. However, positive results are inconsistent and these studies often have small sample sizes.

Many doctors no longer recommend CPM machines because newer research does not support their use. Ask your doctor if they recommend using alternative treatments for recovery.

CPM machines are most commonly used after knee surgery. They can also be used to treat the hip, shoulder, and elbow joints. They have also been used for the treatment of chronic non-specific back pain.

CPM machine for after knee surgery, including total knee replacement

Although CPM machines are sometimes used after knee reconstructive surgery, a number of studies have found they have limited or no benefit.

A 2014 study found that CPM used after surgery to repair intra-articular knee fractures offered no benefit.

Some studies have found more positive results, but the use of CPMs remains controversial.

A 2019 study examined the effect of CPM on a group of 163 patients under the age of 20 who underwent ACL reconstructive surgery. The researchers found that those patients who received CPM treatment were less likely to need a second surgery to break up scar tissue within 6 months of surgery.

A 2018 review of studies found that implementing CPM early in treatment with a rapid progression in range of motion was associated with better recovery than a longer duration of CPM use.

CPM machine for your hip

CPM machines may also be prescribed after hip surgery. A 2017 study found that use of CPM after arthroscopic surgery to correct hip impingement was associated with improved hip flexion post-surgery.

CPM machine for your shoulder

Your healthcare provider may recommend CPM after shoulder surgery in some cases.

A 2016 study compared the benefits of CPM and physiotherapy for people with diabetes undergoing surgery for adhesive capsulitis, also known as frozen shoulder. The researchers found that both CPM and traditional physiotherapy led to improved recovery at 12 weeks. However, patients that used CPM had more distinct improvement in pain levels and function.

CPM machine for your elbow and arm

Physical therapy and CPM are two common treatment options after elbow surgery. However, current evidence suggests that the use of CPM may be redundant and often ineffective.

A small 2020 study found that adding CPM to a traditional rehabilitation program for wrist fractures offered no additional benefit.

CPM machine for your lower back

CPM machines may help treat chronic non-specific back pain. Non-specific pain means that it’s not caused by a specific disease or condition.

A small 2015 study examined the potential benefits of 3 weeks of self-administered CPM on a group of 36 people with mild to moderate non-specific chronic back pain. The researchers found that patients who used the CPM machine for 10 minutes one to three times per day reported less pain at the end of the 3 weeks.

Confirm with your doctor that a CPM machine is right for you, and ask about alternative treatments. Recent research does not support their effectiveness in all situations.

Your healthcare provider and the manufacturer’s instructions that come with your device can best instruct you how to use your CPM machine.

Most often, the device is used while lying in bed or on another comfortable surface. Usually, the machine comes with a remote control that lets you set the extension and flexion limits as well as the speed. You can start or stop the machine by using the remote.

There will likely be a number of knobs and straps on the machine that allow you to fit the machine to the length of your arm or leg. Your healthcare provider can show you how to best adjust the device.

How long should you use a CPM machine?

The amount of time you should use your CPM machine depends on the type and extent of your surgery. Typically, CPM machines are used for 4 hours per day for 4 weeks after hip surgery. A typical timeframe after a knee replacement is 3 weeks but can be shorter or longer.

Some doctors still recommend the use of CPM machines, though many recent studies have questioned their effectiveness. The American Physical Therapy Association recommends avoiding CPM after knee surgery unless formal physical therapy is not possible.

APTA says that the limited benefit is offset by the additional cost and risks caused by long-term bedrest.

A 2017 study found that people with obesity had less favorable outcomes when using a CPM than people without obesity.

If you feel pain, tenderness, or are otherwise concerned, stop using your CPM machine and contact your healthcare provider.

CPMs usually cost upward of $2,000 to buy, but in most cases renting is a less expensive option. According to one CPM rental company, the rental price starts at $425 for 3 weeks with an extra $100 for each week after. Specialty CPMs start at $775 to rent.

Many types of health insurance including Medicare cover the cost of CPM machines. Medicare Part B covers home-use CPM machines after knee replacement surgery for 21 days.

CPM machines were historically used after knee, hip, shoulder, and elbow surgery to help minimize stiffness and increase range of motion. In recent years, the scientific community has begun to question the benefit of CPM use, and many doctors no longer recommend CPM machines following surgery.

If you’re unsure whether you would benefit from using a CPM after surgery, speak with your healthcare provider.