Continuous Passive Motion (CPM) Machine After Total Knee Surgery: Benefits for TKA Recovery

I have witnessed the evolution of rehabilitation techniques following total knee arthroplasty (TKA) over the past four decades of being an orthopedic physical therapist.

Over that period of time, I have seen the waxing and waning of the use of the continuous Passive  Motion machine.

A pivotal advancement in post-surgical care initially was the adoption of the Continuous Passive Motion (CPM) machine. This device gently flexes and extends the knee joint, which is sometimes helpful for fostering a conducive environment for healing.

This article delves into the possible benefits of incorporating a CPM machine in your recovery regimen after TKA, from mitigating pain and swelling to enhancing the restoration of mobility and function in the knee joint.

Understanding Continuous Passive Motion (CPM) After Total Knee Replacement

After undergoing a total knee replacement, also known as total knee arthroplasty, the road to recovery starts with rehabilitation to ensure the best outcomes for your new knee joint. One aspect of post-surgical recovery is the introduction of a Continuous Passive Motion (CPM) machine, a device designed to gently flex and extend the knee joint to facilitate healing.

Implementing continuous passive motion after total knee replacement was initially considered vital because it had the reputation of helping maintain the range of motion, reducing swelling, and minimizing scar tissue formation.

The use of a CPM machine following total knee replacement has been shown to support the healing process, providing the injured knee with a systematic approach to regaining its function.

My experience has caused me to consider CPM as an adjunct treatment procedure only if there is inadequate control of pain.

My patients do much better following the passive self-stretches in my rehabilitation protocol, however, on rare occasions, a patient experiencing pain at 7 out of 10 or above continuously, even when taking break-through pain medication, has benefited from a Continuous Passive Motion machine.

The CPM machine was not intended to “stretch” the knee into extension or flexion. The parameters for setting the range of motion limit are always just short of stretching with the hopes that the range of motion can be increased either at that session or at the next session.

Most importantly for me, the CPM never stretches the knee range of motion into extension, the most important aspect of range of motion, because it has a six-week window of opportunity to get the knee out straight before knee manipulation under anesthesia is a surgeon’s consideration
Read my articles:
The Most Important Exercise After Total Knee Replacement
Total Knee Replacement Manipulation: (When & Why To Consider)

When I look online for an answer to the question: “Should I use CPM machine after total knee surgery”, this is they typical information I see: “By initiating passive motion early after surgery, patients can experience less discomfort and a potentially quicker return to daily activities. A well-structured program with a CPM machine, complemented by active rehabilitation exercises, forms a solid foundation for restoring the function of your knee and enhancing the longevity of your total knee surgery results”.

After seeing many total knee replacement patients over the past four decades, some using CPM machines and most not using the CPM machine, I come down strongly on the side of not using the CPM, with the exception of that rare patient in extreme unrelenting prolonged pain after being discharged to home.

The Role of CPM Machines in Knee Surgery Recovery

My forty years of experience as an orthopedic physical therapist, including being a hospital-based therapist seeing total knee patients bedside immediately after surgery, as a home visit physical therapist seeing the patient for about three weeks post-surgery until ready for outpatient physical therapy, and owning my own outpatient physical therapy clinic with twenty employees, I can tell you the only place I have seen CPM used is in the patient’s home after hospital discharge but before being ready for the outpatient clinic

In the home setting, the CPM is delivered by a non-medical employee of the rental company, the CPM is set up for the patient to use, but I have yet to see a CPM machine set up correctly.

Even if set up correctly there is a lot of “slop” in the machine-knee interaction and it is not, in my opinion, functional to improve any aspect of the range of motion (ROM).
I have, however, seen CPM to be somewhat effective for patients experiencing above-normal expectation levels of pain.

I think the CPM machine plays a part in rehabilitation for a very small segment of the total knee replacement population.

Another downside of the CPM is how surgeons instruct the patients in the use of the machine. Patients are typically told to use the machine for one hour at a time for two to three sessions daily.

That requires the patient to be in bed on their back for a good portion of the day.
I would rather my patients be sitting up or doing some activities of daily living than be in bed all day.

At the beginning of the inception of employing CPM into a total knee replacement rehabilitation program, there was a lot of hope and optimism.
More recently, I have seen most of my referring physicians discontinue the recommendation of using a CPM.

This is my experience and opinion, but it certainly is not what I am reading online.

Benefits of CPM For Enhanced Recovery After Knee Surgery

As an orthopedic physical therapist initiating post-surgical total knee replacement rehabilitation protocols, I think there is the rare patient who has post-surgical pain that is not controlled by break-through pain medication and can experience decreased pain levels using a Continous Passive Motion machine.
Read my article: A PT’s Total Knee Pain Expectations: (Day 1 through Day 30)

I’m not sure of the mechanism that causes the pain reduction, but as most pain is the result of swelling, my suspicion is that CPM helps move the excessive edema out of the knee joint.

I have not seen any benefit of increased range of motion more quickly than my protocols of self-stretching I give my patients, as I’m sure most therapists recommend in their rehab protocols also.

How Continuous Passive Motion Aids TKA Rehabilitation

The online literature I read says, “Upon completion of a total knee arthroplasty, the journey to restored mobility often incorporates the use of a Continuous Passive Motion (CPM) machine. This device is frequently recommended by surgeons following total knee arthroplasty to enhance recovery through improving range of motion, promotes circulation, decreases swelling and stiffness, and is vital for tissue repair.”

Except for the claim of decreasing swelling, none of the other claims have I found truthful while treating my patients.

I have seen extreme cases of unrelenting pain that CPM did help, and I think it was through the possibility that the CPM helped reduce the swelling in the knee.

As for the other claims, I find my patients to benefit much more by wearing TED hose, doing ankle pumps, doing the self-stretch exercises as I instructed, and elevating the legs when relaxing, often in their recliner chairs with the application of cold therapy.
Read my articles:
Can I Sit In A Recliner After Knee Replacement? A PT’s Advice
Ice After Total Knee Replacement: A PT’s Complete Guide.

In conclusion, I disagree with almost everything on the internet about the value of the Continuous Passive Motion machine benefits after total knee replacement with the exception of the possibility of pain reduction in that unfortunate, albeit rare individual that suffers increased pain past the ability of pain medications to control adequately.

This mindset, although contrarian to online information, comes from decades of being an orthopedic physical therapist seeing total knee replacement patients in all phases of their rehabilitation recovery journey; and my referring surgeons decreased enthusiasm for the CPM promise.

Read my other articles about Total Knee Replacement

Dr. Robert Donaldson

Dr. Donaldson is dually licensed; physical therapy in 1975 and doctor of chiropractic in 1995. He held credentials of Orthopedic Clinical Specialist in physical therapy for 20 years, QME in California, and taught at USC. He owns and operates an orthopedic physical therapy practice. See "About Me" page.

Recent Posts