A continuum-mechanical model of the musculoskeletal system in a residual limb and its application in forward simulations to analyse socket-limb interaction

Abstract

The musculoskeletal system of the residual limb in above-knee amputees features complex skeletal muscle anatomy and physiology. Development of high-resolution 3D biomechanical models for forward simulations necessitates the integration of computational imaging, continuum mechanics and numerical optimisation. This thesis enhances the understanding of residual limb biomechanics by examining inherent stresses of skeletal muscle in the form of initial fibre pre-stretch and muscle co-activation and their effects on joint kinematics. To speed up the creation of detailed 3D musculoskeletal models, a semi-automated, unsupervised segmentation process using 2D diffeomorphic mapping of MRI sequences is introduced. The phenomenological constitutive laws of the muscle-tendon complex are extended to a continuous formulation across the transition zones and capture the spatial variations in isotropic and passive stiffness from muscle belly to tendon ends. Through system-level musculoskeletal finite element simulations, the thesis investigates socket-limb interactions and mechanical comfort during double-limb support, as well as joint kinematics during muscle activation-driven open-chain hip motion. The insights from these simulations deepen the understanding of how anatomical and physiological factors affect residual limb biomechanics. These outcomes can be used to design prosthetics and wearables that accurately account for subject-specific biomechanics.