Abstract:
This study investigates how the complex, three-dimensional (3D) architecture of the rectus femoris and vastus intermedius muscles affects their biomechanical behavior, specifically their muscle fiber excursions (changes in length during joint motion). Traditional lumped-parameter models, which use simplified 2D geometry, often fail to capture the nuances of intricate muscle structures. To address this, the authors developed detailed, 3D finite-element (FE) models of these two muscles based on MR images, incorporating realistic 3D fiber trajectories, internal aponeuroses, and a transversely isotropic constitutive model to describe the tissue's material properties.
The researchers simulated knee motion from full extension to 100° of flexion and compared the fiber excursions predicted by their 3D FE models to those from conventional lumped-parameter models. The 3D models revealed that fiber excursions were highly non-uniform across the muscles, ranging from 55% to 70% of the total muscle-tendon unit excursion in the rectus femoris, and 55% to 98% in the vastus intermedius. In contrast, the lumped-parameter models predicted much larger and uniform excursions of 86% and 97%, respectively. This discrepancy suggests that simpler models overestimate fiber length changes, which would lead to inaccurate predictions of the muscle's force-length behavior. The study concludes that for muscles with complex architectures, detailed 3D FE models are necessary to accurately represent their internal mechanics and improve the fidelity of musculoskeletal simulations.
