Biomechanical analysis of the muscular and ligament behavior of the knee joint through a subject-specific computational model

Understanding the biomechanical effects of various factors on knee behavior is crucial for the development of an optimal surgical treatment that can restore normal knee function. To date several mathematical models have been developed to predict the kinematic and dynamic behavior of the knee joint1,2. In this work we present a multibody dynamics-based model created with Working Model 3D (MSC.Software Corp., Santa Ana, CA) aimed to analyze soft tissues and contact forces between bony structure in a physiological joint; bones were reconstructed using magnetic resonance images of a fully extended knee; the model was completed with anterior and posterior cruciate ligaments, lateral and medial collateral ligaments and quadriceps muscle. Ligaments were assumed to be elastic and their mechanical properties were described by a non linear force-length curve; stiffness values and reference strains in fully extended knee were based on literature data3. Ligaments were treated as non-linear springs and divided in multiple bundles to analyze their specific behavior while quadriceps muscle was modelled as a non-linear actuator. A simulation of a loaded squat starting from 0° until a maximum flexion angle of 120° was performed with a constant vertical hip load of 300 N. Preliminary results showed that tibio-femoral contact forces increased with flexion and their values are in agreement with literature4. Ligament forces and lengthening patterns evaluated during flexion well reflect literature data5. Once validated, the model will be used for subject-specific analyses of ligaments, muscular behavior and contact forces and integrated with mechanical prostheses for a pre-operatory assessment