Continuous passive motion (CPM) is a treatment method designed to aid in the recovery of joints immediately after trauma or surgery. 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 (which would be unimportant in the event of joint replacement), 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.