Simply put, it passively moves the affected joint through the Range of Motion (ROM). It may seem counterintuitive but moving the joint sooner after your surgery can speed your recovery and decrease the amount of pain. There is almost 100 years of scientific literature proving the benefits/value of the CPM. One of the things that can cause the most pain is the buildup of fluid inside the affected joint. The buildup of excess fluid puts extra pressure on your nerves and can also limit your range of motion by making the joint feel stiff. The CPM helps remove excess fluid from the joint and stimulates blood flow to the area. If your joint is less stiff and less painful, you are more likely to experience a positive outcome. If your doctor doesn't prescribe a CPM, don't be afraid to request one.