A Novel in Vitro Experimental Design for Biomechanical Testing of Patellofemoral Joint Kinetics and Kinematics

Introduction: Complications arising from the patellofemoral joint (PFJ) represent the third most common cause for revision in total knee arthroplasty (TKA). Previous in vitro biomechanical studies have altered the native attachments of muscles controlling the PFJ. The purpose of this study was to design an in vitro biomechanical setup that would allow testing of both native and arthroplasty knee joints, specifically the PFJ, without disturbing the native attachments of the quadriceps and hamstrings muscles. Methods: After finalising a prototype, a pelvis-to-toe human cadaver specimen was tested. The simVITRO platform was used to simulate movement and control force trajectories. A motion capture system was used to capture the motion of the bones and to measure knee flexion angle and patellar movement with respect to the femur. The forces applied in the PFJ were measured using a custom patella sensor. Results: Displacement of the reflective cluster attached to the femur was measured during compression loading at different flexion angles, passive flexion and stairs descent trajectory. The femur showed less than 1 mm and 3 mm displacement with respect to the femur clamp in passive flexion and stairs descent. The most translation of 8.37 mm (<2% average femur length) was observed at 90° flexion which occurred at 483 N simulated compression force. Conclusion: This novel design provides a methodology for studying the biomechanics of the PFJ in vitro that preserves the soft tissues influencing the behaviour of the joint. This setup provides a biomechanics model that can be utilised to better understand and study the PFJ in vitro.