CPM machine for hips, knees: How does it work?

CPM machine for hips, knees: How does it work?

A continuous passive motion (CPM) system enables post-operative movement of the joints. After surgery on joints such as the knee or hip, a person can use a CPM machine

Some people can find that a CPM machine helps to improve motion range, but research is uncertain as to whether or not they have any substantial recovery benefits.

A person should not be shocked for that reason if their doctor or surgeon does not recommend using this device.

Continue reading to learn more about how a CPM machine works, the possible benefits of using it on various joints and how a person can get a home-use CPM machine.

What is a CPM machine?

CPM machines can help increase a person’s range of motion after undergoing joint surgery.
CPM machines can help increase a person’s range of motion after undergoing joint surgery.

A CPM machine is a piece of equipment that a person may use while having joint surgery to help with recovery. The concept behind CPM machines is for them to expand motion range.

They provide continuous motion sessions for joints a person can’t move freely.

People can feel pain after having undergoed surgery while attempting to move their joint. It can cause them to stop moving the joint which can lead to stiffness, loss of movement, and scar tissue development.

How does it work?

After undergoing surgery people may use a CPM machine to increase the range of motion of a joint.

Some research suggests that a CPM machine could:

  • reduce pain
  • reduce the length of hospital stays
  • reduce the need for manual movement of the joint while people are under anesthetics

Nevertheless, the authors of the study conclude that insufficient data existed to determine the effect of a CPM system on the global evaluation of efficacy of care by participants.

A CPM system offers normal joint movements without the need for people to use their muscles. This can help loosen a joint which can be rigid and hard to push.

An person can position the affected part of the body into the CPM machine and control the machine with a handheld device. They may, for example, use the control to start and stop motion, as well as change movement speeds.

The amount of time a person requires to use a CPM machine for depends on their condition and on the joint on which they use it. A healthcare professional may give guidance about how and for how long to use the tool.

For example , a person using a hip recovery CPM machine may use it for a duration of 4 weeks for 4 hours a day. Healthcare professionals may encourage others to use the machine at the same time for 45 minutes, and to rest between sessions.

Benefits of a CPM machine

A CPM machine may have benefits for the following joints:


A CPM system can be used by some to recover from knee replacement surgery.

One 2014 study investigated the effectiveness of using a CPM system following knee replacement surgery. The analysis included 24 studies which included 1,445 participants.

This has found the following advantages to people using a CPM machine:

  • At week 6, participants using a CPM machine could bend their knee around 2 degrees more than those who did not use CPM.
  • At week 6, participants using a CPM machine scored their pain at an average of 2.6 out of 10, compared with 3 out of 10 for those who did not use CPM.
  • At month 6, people using CPM rated their quality of life one point higher than those not using a CPM machine.
  • On average, people using CPM had a 15% risk of experiencing a medical problem, compared with 16.3% for people not using CPM.
  • On average, people using CPM had a 1.6% risk of needing manipulation of the knee under anesthetics, compared with a 7.2% risk among people not using CPM.

Nevertheless, the authors conclude that for people who underwent knee replacement surgery, CPM did not offer any substantial change in outcome.


After undergoing hip surgery, physical therapy by using a CPM machine can aid recovery.

The aim of physical therapy is to:

  • increase flexibility
  • improve range of motion
  • reduce inflammation
  • relieve painful symptoms
  • reduce the risk of stiffness and the development of scar tissue

Having a CPM machine may help to minimize motion loss, which a person will need intensive physical therapy to recover.

For the hip, a person may use a CPM machine for a 4-week span of 4 hours a day.

Buying or renting a CPM machine

A person may get to use a CPM machine at home. They may be able to apply to their doctor for a CPM machine, and have the machine arrive at the doctor on the day of their service.

When an individual has access to Medicare health insurance, they could be eligible for use on their home with a CPM machine. When they meet the requirements that require a CPM machine following knee surgery, Medicare will offer up to 21 days for patients to use a CPM machine at their home.

Users should negotiate costs with their doctor, and whether they should rent or buy the unit. A CPM computer can also be bought online or from companies that offer medical equipment.


Using a CPM machine can help to increase motion range after undergoing joint surgery. A person may use a CPM machine after having had knee or hip surgery.

Evidence has so far been vague as to whether or not a CPM system provides any significant benefits for recovery after surgery.

The effects of a CPM machine can depend upon the condition of the individual and the joint affected. Using a CPM system can in some cases help improve motion range and relieve pain.

Individuals should talk with their doctor about the potential benefits of using a CPM device.

If a person is experiencing any negative effects from using a CPM machine — such as increased pain , swelling, or numbness — they should avoid using it and immediately contact a doctor.