Continuous passive motion is a rehabilitation technique where the knee is very gradually bent and straightened, over periods of hours, using a CPM machine.
Continuous Passive Motion, Early Weight Bearing, and Active Motion following Knee Articular Cartilage Repair. Howard JS, Mattacola CG, Romine SE and Lattermann C. Cartilage. 2010 Oct; 1(4): 276–286.
Use of Continuous Passive Motion Reduces Rates of Arthrofibrosis After Anterior Cruciate Ligament Reconstruction in a Pediatric Population. Bram JT, Gambone AJ, DeFrancesco CJ, Striano BM and Ganley TJ. Orthopedics. 2019 Jan 1;42(1):e81-e85. doi: 10.3928/01477447-20181120-04. Epub 2018 Nov 28.