The lack of an efficient modelling-simulation-analysis workflow for creating and utilising detailed subject-specific computational models is one of the key reasons why simulation-based approaches for analysing socket-stump interaction have not yet been successfully established. Herein, we propose a novel and efficient modelling-simulation-analysis workflow that uses commercial software for generating a detailed subject-specific, three-dimensional finite element model of an entire residual limb from Diffusion Tensor MRI images in <20 min. Moreover, to complete the modelling-simulation-analysis workflow, the generated subject-specific residual limb model is used within an implicit dynamic FE simulation of bipedal stance to predict the potential sites of deep tissue injury. For this purpose, a nonlinear hyperelastic, transversely isotropic skeletal muscle constitutive law containing a deep tissue injury model was implemented in LS-DYNA. To demonstrate the feasibility of the entire modelling-simulation-analysis workflow and the fact that detailed, anatomically realistic, multi-muscle models are superior to state-of-the-art, fused-muscle models, an implicit dynamic FE analysis of 2-h bipedal stance is carried out. By analysing the potential volume of damaged muscle tissue after donning an optimally-fitted and a misfitted socket, i.e., a socket whose volume was isotropically shrunk by 10%, we were able to highlight the differences between the detailed individual- and fused-muscle models. The results of the bipedal stance simulation showed that peak stresses in the fused-muscle model were four times lower when compared to the multi-muscle model. The peak interface stress in the individual-muscle model, at the end of bipedal stance analysis, was 2.63 times lower than that in the deep tissues of the stump. At the end of the bipedal stance analysis using the misfitted socket, the fused-muscle model predicted that 7.65% of the residual limb volume was injured, while the detailed-model predicted 16.03%. The proposed approach is not only limited to modelling residual limbs but also has applications in predicting the impact of plastic surgery, for detailed forward-dynamics simulations of normal musculoskeletal systems.

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Homogenised finite-element (FE) skeletal muscle models provide a good trade-off between computational efficiency and physiological realism. This trade-off is in part due to the lack of explicit modelling of muscle fibres (MFs). As a consequence, the organisation of MFs into motor-unit territories (MUTs) is particularly challenging. The current paper presents a possible technique to adress this issue by assigning MUTs in a homogenised sense in terms of muscle volume to FE skeletal muscle models. This method allows control of inter-MUT distance, the amount of intermingling between MUTs and the order of MUT assignment. It was found that both assigning smaller MUTs first and allowing a moderate amount of intermingling significantly influence MUT distributions. This technique allows a simplified and straight-forward way to introduce MUTs into 3D FE skeletal muscle models.

This paper introduces, for the first time, a methodology to achieve a forward dynamics simulation of the musculoskeletal system using three‐dimensional continuum‐mechanical skeletal muscle models. This is achieved by coupling one‐ and three‐dimensional skeletal muscle models. The feasibility of this methodology is demonstrated through a forward dynamics simulation of the upper limb involving the biceps and triceps muscle. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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