A portable medical device suitable for use in continuous passive motion (CPM) rehabilitation programs has a lightweight modular frame for ease of storage and portability. In one embodiment a proximal sling module is pivotally connected to a distal sling module with is pivotally connected to a heal plate module. Another embodiment includes a base module is pivotally connected to a proximal sling module which is pivotally connected to a distal sling module pivotally connected to a link pivotally connected to the base. The joint of a patient's limb is flexed through a range of motion by pivoting the distal sling module relative to the proximal sling module. The device is powered by a motor and worm gear directed by a controller.