 The purpose of this study is to determine how well an active motion device, Camoped, works compared to a continuous passive motion device, CPM, for rehabilitation after partial or total knee replacement. It is hypothesized that the Camoped active motion device will provide outcomes equal to or superior than the CPM. 110 patients will be randomized during the course of the study. Participation lasts approximately 4 weeks. Data for patients who begin the trial, but choose to drop out or are lost to follow up will not be included in analysis. 