Automated Hemostasis in Limb Trauma: FEM Insights for Tourniquet Optimisation

Abstract

Haemorrhage is the leading cause of preventable death in military operations, often resulting from explosions, gunshots, stabbings, or cuts. Limbs are particularly vulnerable, accounting for nearly 55% of combat-related injuries, and rapid blood loss can lead to over half of deaths within minutes and almost one-third within hours. These statistics highlight the urgent need for rapid and reliable haemorrhage control, particularly in situations where immediate human intervention may be delayed or impossible.To address this critical problem, an automated primary hemostasis system was developed to arrest bleeding without human assistance. The design of its signal-triggering mechanism was informed by finite element method (FEM) simulations, which provided a quantitative understanding of tissue mechanics under tourniquet application. Human soft tissues exhibit complex behaviour due to their multilayered structure, heterogeneity, anisotropy, and viscoelasticity, necessitating nonlinear constitutive models. In this work, skin, subcutaneous adipose tissue, and muscle were modelled as nearly incompressible, isotropic hyperelastic materials using a Neo-Hookean formulation, whereas bones were considered rigid. The Neo-Hookean model captures tissue response through two key parameters: the shear modulus, which governs deformation under shear, and the bulk modulus, which defines resistance to volumetric compression.A detailed three-dimensional model of the upper limb was reconstructed from biomedical imaging data, including skin, adipose tissue, muscle, and humeral bone. The discretised model comprised over 850,000 tetrahedral elements, with material properties assigned according to tissue type and scaled to anatomical geometry. Boundary conditions permitted free displacement of soft tissues, while bone nodes were constrained axially. Tourniquet application was simulated by imposing prescribed displacement fields derived from three-dimensional indentation maps. To ensure numerical stability in the presence of nonlinear tissue behaviour, compression was applied incrementally using a conservative predictor strategy.Simulation results revealed striking patterns of tissue deformation. Maximum displacement occurred at the tourniquet centre, predominantly in the radial direction, while axial displacement dominated regions outside the compressed zone. Muscle surface strain increased progressively with compression intensity and exhibited a diffuse spatial distribution, whereas stress concentrations were localised at tissue interfaces. These mechanical patterns were interpreted in the context of physiological blood flow, both at rest and during intense exertion. Elevated arterial pressure and increased flow rates accelerate haemorrhage, shortening the window for effective intervention and emphasising the importance of timely hemostatic control.Integrating FEM-based tissue mechanics with hemodynamic considerations provides critical insights into the efficiency of haemorrhage control strategies. This approach not only informs the design and optimisation of tourniquets but also guides the development of automated hemostasis systems capable of rapid deployment in high-risk scenarios. By linking quantitative tissue deformation with clinical outcomes, the study offers a powerful framework for improving survival rates in military and civilian trauma situations, highlighting how biomechanical modelling can directly influence life-saving interventions.

Keywords: Haemorrhage Control, Finite Element Method (FEM), Tourniquet Biomechanics, Limb Trauma, Automated Hemostasis Systemno

DOI: 10.54941/ahfe1007469