Design of Adjustable Spherical Four-Bar Linkages As Continuous Passive Motion Devices for Anatomic Joints Rehabilitation

Abstract

Abstract Continuous passive motion (CPM) is an important treatment in postoperative rehabilitation of human joints. It can improve the range of motion (ROM), reduce joint stiffness and accelerate the recovery process. The concept of CPM can be applied in many joint rehabilitation applications, including ankle joints, knee joints and elbow joints. However, even within a single type of joint, the ROM can be significantly different from person to person. Adjustable spherical linkage is appropriate for these applications. The following procedure is introduced: synthesize the first set of positions and selects the center point and circle point. Then, with the same center point and circle point, by altering some design parameters, i.e., the length of the input link and output link, a new set of positions can be synthesized. This idea is more practical in three-plus-two position synthesis, but can also be applied to four-plus-three position synthesis, with a significant increase in complexity. The above synthesis method can be applied to any generic adjustable spherical linkage application. In this paper, this method is tailored to an anatomical joint application for CPM machine design. Clinical motion data is directly used to define the orientation of the joint. The details of this method are illustrated by an example, the ankle joint. The first set of synthesis positions is obtained from the clinical data and a list of designed candidates is presented. After that, we introduced a second set of synthesis positions from the clinical data. The adjustable spherical linkage is synthesized with the common ground pivot. By using this method, an adjustable CPM machine can be designed to cover the minimum ROM and maximum ROM. This machine can be used to more than one patient, as well as throughout a single patient’s full recovery.