What is a CPM machine and Should You Use It?
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CPM stands for Continuous Passive Motion machine. This is a mechanical device that provides continuous passive motion for a joint, most commonly the knee, while the person lays on their back.
To use the CPM machine, you line up your knee joint with the fulcrum of the device and then you are strapped in above and below the knee. The machine passively bends the knee at a predetermined range of motion (ROM) and speed. The typical speed is 2 cycles of flexion and extension per minute. Typically, an individual will use the CPM 2-3x per day starting the same day or day after surgery and will continue to use the device for a couple days. The ROM of the device starts small and is gradually increased based on patient tolerance.
The main goal of using a CPM is to improve knee ROM in the acute phase right after surgery. The device may also be discharged for home use if the patient/caregiver is able to manage and setup the CPM machine independently.
Let see what the research shows…
- One study by Beaupre et al. (2001) compared three different groups of patients: one group received standard exercises, one group received sliding board exercises and standard exercise, and one group received standard exercise and used the CPM machine. The researchers measured the patients’ knee ROM pre-operatively, 5 to 7 days post-op, 3 months post-op, and 6 months post-op. They found no statistical difference in knee ROM between any of the groups at any of the measurement periods.
- Another study by Bruun-Olsen et al. (2009) compared two groups. One group received active exercises with CPM use and the other group just received active exercises without CPM use. They measured knee ROM at pre-op, 1 week post-op, and 3 months post-op. Again, they found no statistical difference in knee ROM measurements between the two groups at any of the measurement periods.
- A study by Alkire et al. (2010) compared two different groups. One group received PT 2x/day and no CPM and the other group received PT 2x/day and CPM 3x daily for 3 days. Once again, no statistical differences were found in knee ROM measurements between the two groups.
- Lastly, a 2015 study by Joshi et al. compared two different groups. One group received physical therapy and CPM use and the other group received just physical therapy. The researchers results showed no clinically relevant difference in knee ROM between the groups at any measurement period.
From the results of these studies, it is clear that using a CPM machine in the acute phase following surgery provides no additional benefit compared to standard physical therapy treatment and exercises. In fact, CPM use may have negative effects as the person must lay in bed for extended periods of time and this time can be used for more active and functional exercises.
For these reasons, we recommend that the majority of knee replacement patients should not use a CPM machine after surgery and instead, focus on more active ROM exercises.
1. Beaupre, LA, Davies, DM, Jones, CA, Cinats, JG. Exercise Combined With Continuous Passive Motion or Slider Board Therapy Compared With Exercise Only: A Randomized Controlled Trial of Patients Following Total Knee Arthroplasty. Phys Ther 81: 1029-1037, 2001.
2. Bruun-Olsen, V, Heidberg, KE, Mengshoel, AM. Continuous passive motion as an adjunct to active exercises in early rehabilitation following total knee arthroplasty- a randomized controlled trial. Disab Rehab 31: 277-283, 2009.
3. Alkire, MR, Swank, ML. Use of Inpatient Continuous Passive Motion Versus No CPM in Computer-Assisted Total Knee Arthroplasty. Orthop Nurs 29: 36-40, 2010.
4. Joshi, RN, White, PB, Murray-Weir, M, Alexiades, MM, Sculco, TP, Ranawat, AS. Prospective Randomized Trial of the Efficacy of Continuous Passive Motion Post Total Knee Arthroplasty: Experience of the Hospital for Special Surgery. J Arthroplasty 30: 2364-2369, 2015.
5. Lazaro, B, Terry, C, Westmoreland, C. Continuous Passive Motion Versus Active-Assistive Exercise During Acute Rehabilitation of Total Knee Arthroplasty. Unpublished Manuscript. Accessed 1 August 2018.
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