Integrating modelling, motion capture and x-ray fluoroscopy to investigate patellofemoral function during dynamic activity

Accurate measurement of knee-joint kinematics is critical for understanding the biomechanical function of the knee in vivo. Measurements of the relative movements of the bones at the knee are often used in inverse dynamics analyses to estimate the net muscle torques exerted about the joint, and as inputs to finite-element models to accurately assess joint contact. The fine joint translations that contribute to patterns of joint stress are impossible to measure accurately using traditional video-based motion capture techniques. Sub-millimetre changes in joint translation can mean the difference between contact and no contact of the cartilage tissue, leading to incorrect predictions of joint loading. This paper describes the use of low-dose X-ray fluoroscopy, an in vivo dynamic imaging modality that is finding increasing application in human joint motion measurement. Specifically, we describe a framework that integrates traditional motion capture, X-ray fluoroscopy and anatomically-based finite-element modelling for the purpose of assessing joint function during dynamic activity. We illustrate our methodology by applying it to study patellofemoral joint function, wherein the relative movements of the patella are predicted and the corresponding joint-contact stresses are calculated for a step-up task.