Update of the articular representation of the TLEM 2.0 musculoskeletal model

To provide reliable results, musculoskeletal models must accurately represent human anatomy and be consistent with anatomical function. While considerable effort has been made to improve the muscular modeling, the same is often not true for the kinematic chain representing skeletal mobility. The aim of this work is therefore to take one of the most comprehensive musculoskeletal models, the TLEM 2.0, and improve its articular representation. Based on bone morphology, 3D articular kinematics of the tibio-femoral, patella-femoral, talo-tibial, and calcaneo-talar joints have been reconstructed by joint congruence maximization. Given these reference motions: the most isometric fibers for the main ligaments at the knee and the ankle have been identified; contact points and normals have been defined; the neutral configuration of the model has been defined. With respect to the original kinematic chain based on revolute joints, the one here proposed presents no joint distraction nor copenetration between the bones, together with a more physiological ligament elongation during joint motion, resulting in an articular representation more consistent with the TLEM 2.0 anatomy. These improvements substantially strengthen the anatomical fidelity of TLEM 2.0 and provide a robust foundation for next-generation MSK models. The updated dataset enables more reliable estimation of ligament and contact forces, supports the development of advanced rigid or deformable joint mechanisms, and offers a generalizable framework for subject-specific personalization whenever joint geometry is available. This represents a significant step toward MSK models capable of reliably capturing articular function under load.