 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. Patients undergoing either partial or total knee replacement will be given the opportunity to participate. If they elect to participate, preoperative data will be collected including demographics, measures of strength, balance and knee bending, as well as surveys regarding current physical and mental health, as well as knee function. After surgery, patients will be randomly selected to receive either the Camoped or the CPM for use during their rehabilitation. After discharge, participants will be asked to maintain a daily diary tracking their use of the assigned device, as well as their daily pain levels. At a visit 4 weeks after surgery, participants will be asked to complete a series of surveys pertaining to their health and knee function, as well as to perform tests of strength, balance and knee bending. These results will be used to determine if one device produces superior rehabilitation results following total or partial knee replacement surgery. 