Continuous passive motion
Continuous passive motion (CPM) devices are used during the first phase of rehabilitation following a soft tissue surgical procedure or trauma. The goals of phase 1 rehabilitation are: control post-operative pain, reduce inflammation, provide passive motion in a specific plane of movement, and protect the healing repair or tissue. CPM is carried out by a CPM device, which constantly moves the joint through a controlled range of motion; the exact range is dependent upon the joint, but in most cases the range of motion is increased over time.
CPM is used following various types of reconstructive joint surgery such as knee replacement and ACL reconstruction. Its mechanisms of action for aiding joint recovery are dependent upon what surgery is performed. One mechanism is the movement of synovial fluid to allow for better diffusion of nutrients into damaged cartilage, and diffusion of other materials out; such as blood and metabolic waste products. Another mechanism is the prevention of fibrous scar tissue formation in the joint, which tends to decrease the range of motion for a joint. The concept was created by Robert B. Salter M.D in 1970 and, along with help from engineer John Saringer, a device was created in 1978.
One of the largest CPM outfitters for rent or sale is The Medcom Group, Ltd. http://www.medcomgroup.com/
CPM Following Knee Arthroplasty
There are contradicting studies in regards to knee CPMs. Unfortunately, many insurance companies, doctor's offices, and other medical establishments do not want to claim financial responsibility for these medical devices, especially in the United States. That being said, some research concludes that CPMs do not help the recovery process. However, these studies are designed to make CPMs fail. For example, CPMs used in conjunction with physical therapy yielded the same results as physical therapy alone. However, in this study, physical therapy was administered to patients twice a day for 18 days  The usual PT prescription for a #REDIRECT TKA is only twice per WEEK  Even so, this CPM condemning study had to report their findings in favor of CPM use due to ..."improved short-term range of motion in patients with limited range of motion at the time of discharge after total knee arthroplasty when added to a semi-regular PT program.".
Some CPM investigations have yielded negative feelings and results towards CPM use is due to poor usage of the device 
CPM efficacy is contingent on the presence of larger motion arcs. Surprisingly, the range of motion (RoM) the knee actually experiences while in a CPM machine has experienced only 68%-76% of the programmed CPM arc. These percentages should be increased throughout the rehabilitation process
, but many healthcare providers fail to follow up adequately with patients regarding this vital step of the recovery process 
CPMs are extremely effective in pain management. Continuous motion of a joint allows for synovial fluid to be naturally pumped throughout it. This leads to efficient nutrient delivery to the damaged area, reduced inflammation, and overall reduced pain  A study lead by Dr. Rajesh N. Maniar, MS, MCh found little difference between a very short- term study (only 3 days) the recovery of patients who did and did not use a CPM. However, he removed pain as a contributing factor  This was completed by The journal of arthroplasty which is a funded organization and may have underlying agendas. This study neglected pain as a factor, but pain is THE LARGEST factor in rehabilitation. If a patient is in too much pain to complete therapy, he/she will shy away from progress because it will hurt too much. Decreased movement, especially in the early stages of recovery can result in the granulation of tissue and the formation of scar tissue. Once scar tissue sets in, it is nearly impossible to regain the range of motion lost due to arthrofibrosis. 
For people who have had total knee replacement without complications, continuous passive motion has not been shown to provide clinically relevant benefits. CPM does not improve long-term function, long-term knee flexion, knee extension in the short or long term, and has not been shown to reduce pain and or increase quality of life. Additionally, CPM is expensive, inconvenient, and brings risk of complication while distracting patients from useful treatment. In unusual cases where the person has problems which prevent standard mobilization treatment, then CPM may be useful. Patient compliance is key to rehabilitation. Furthermore, with patients attempting at-home therapies, most follow orders with improper form that either limits improvement or in some cases, causes harm 
CPM Following Strokes
There are limited occupational therapies that are fully supported across a spectrum of patients. The fundamental movements provided by the CPM units, potentially allows for a remedial and fast progressing therapy. This is according to the University of California. This is an untapped potential for these stroke victims that needs to be further explored, according to the same source. CPM units are a rare form of therapy that directly correlates the amount of use to the amount of progress. It is easy to neglect at-home theraputic exercises for various reasons, but CPMs can be used while watching television or doing anything stationary. This ability to multi-task therapy with recreational activities hold higher promise for patients completing the therapy at home. Completing the therapy at home is just as important as prescribing it. That is why some studies suggest physical and occupational therapy yield better results than CPM units. CPM units should be used supplementary; also, these studies have fully compliant PT and OT patients whereas most patients do not fulfill their at-home exercises as often or with proper form that is suggested in these studies.
- Salter RB (May 1989). "The biologic concept of continuous passive motion of synovial joints. The first 18 years of basic research and its clinical application". Clin. Orthop. Relat. Res. (242): 12–25. PMID 2650945.
- Salter RB, Hamilton HW, Wedge JH, et al. (1984). "Clinical application of basic research on continuous passive motion for disorders and injuries of synovial joints: a preliminary report of a feasibility study". J. Orthop. Res. 1 (3): 325–42. doi:10.1002/jor.1100010313. PMID 6481515.
- American Physical Therapy Association (15 September 2014), "Five Things Physicians and Patients Should Question", Choosing Wisely: an initiative of the ABIM Foundation (American Physical Therapy Association), retrieved 15 September 2014, which cites