Continuous Passive Motion and Loading System Design for the Study of Pro- and Anti-Inflamatory Mediators in Articular Cartilage

Joint diseases are common causes of disability worldwide. Physical activity and weight bearing conditions play an important role in the regulation of joint homeostasis throughout life. The parametric characterization of deleterious and beneficial joint loading regimens influencing the homeostasis of articular cartilage is of great interest from both a basic research and clinical practice point of view. The development of in vivo animal models is critical to investigate the underlying mechanisms mediating the biological response of articular joints to external mechanical stimuli. For this purpose, the design of a device capable of accurately control the joint motion and loading in a small animal is needed. In the present work, an assisted motion system was conceived to perform continuous passive motion (CPM) and continuous loaded motion (CLM) on the knee joint of a small animal in vivo. A major purpose of this system is the study of the inflammatory and anti-inflammatory response of cartilage under several biomechanical environments. Therefore, a key design criterion was to avoid any invasive intervention (i.e. intraskeletal fixators) that may produce an intrinsic inflammatory response and then obscure/mislead the assessment of the biological markers of interest. Other important design criteria include real time control of the knee joint position, angular displacement, cyclic motion frequency and custom load magnitude applied in the axial direction along the tibia.