Ask an answerable question (PICO)：
The symptoms of degenerative arthritis are serious, affecting daily life. Patients are advised to undergo knee replacement to improve and relieve pain and stiffness. After knee arthroplasty, patients will receive Continuous Passive Motion (CPM), but there is not enough information or evidence to teach the patient or to take care of the routine.
The Method and Analysis of Literature Review：
Databases included The Cochrane Library, PubMed, and Embase and are not limited to year and language. A total of 89 articles in English were obtained. Finally, a systematic review with a higher level of evidence was included and RCT literatures were reviewed.
Systematic reviews evaluated the evidence level as level 1 based on the CASP and RCTs using Cochrane RoB 2.0. The quality of the document has some concerns. All subjects underwent knee arthroplasty and were older than 18 years old. The patients received continuous passive exercise for 2 to 6 hours and physical therapy (PT) for 2 hours per day after surgery; the control group received routine PT for 2 to 3 hours.
Conclusions and Recommendations：
CPM has no clinical effect on range of motion and hospital length of stay between the experimental group and the control group. In the future, more rigorous randomized trials are needed to control random assignment and concealment bias for providing clinical reference.