###### Abstract  
This article presents the results of numerical finite element method (FEM) simulations in the Ansys environment of a Boston orthopaedic brace. The geometric model was developed based on the results of digitisation performed by means of a three-dimensional (3D) optical scanner. A test stand for measurement of the brace's field of displacements, utilising a laser electronic speckle pattern interferometer (ESPI), was used to experimentally verify the FEM model. During experimental testing, special attention was given to applying the loads and boundary conditions used in the numerical simulations. As a result, the relative difference between the experimentally and numerically determined displacements in the central part of orthoses amounted to approximately 0.6%. The experimentally verified FEM model was used to determine the force flow lines characteristic of the brace, indicating the general working method of the brace's structure. The primary parts of the orthoses, carrying loads correcting the spine and the position of sites exerting little effort from the perspective of their participation in the orthoses' essential therapeutic application were identified. The results obtained allow for the proposal of methods for mechanical optimisation of the brace's design. The analysis conducted is universal in nature and can be adapted to other types of orthopaedic braces. F 20  
of computed tomography (CT) or magnetic resonance (MR) medical imaging, and sometimes a 3D scan of the torso, are used, from which a body model is obtained, representing the actual structure of the musculoskeletal system [6; 9; 10; 11]. The geometric image of the torso's FEM model, after correction by the computer-modelled spatial field of pressures, is used as the model of the brace's geometry. Due to the difficult issue of contact and the presence of complex anatomical structures in the human torso, in practice, it is not possible to faithfully represent FEM-determined fields of corrective pressures on the torso. In articles by [PERSON] et al. [9] and [PERSON] and [PERSON] [12], the authors compare the effectiveness of braces designed using CAD/CAM computer methods combined with FEM. They emphasise that each of these methods has its pros and cons, and that combining them may bring about better efficacy of bracing. The efficacy of action of the designed braces can be practically verified, for example, through X-ray or CT imaging of the patient wearing the brace. In research, experiments to determine the forces generated in orthosis components, such as the straps that tighten the orthosis, during corrective work, or the forces acting on the orthosis, are important in brace design research. For example, arrays with a large number of pressure sensors placed inside the orthosis are used [13; 14; 15]. Two research directions may be identified. In the first variant, testing is carried out involving the patients [13]. In the other variant, a standard force test stand with three-point loading of the orthoses is used [16]. It can be seen that the current progress in rigid orthoses is focused on a better comprehension of their correction functionalities [4], which are defined, inter alia, by the spatial force field required to act on the trunk, as well as, although less so, by the mechanical characteristics of the orthoses that are required to perform those functionalities. Examples of FEM applied to describe individual braces as an additional option accompanying FEM modelling of the torso can be found in the literature [17], but these brace designs are simplistic and fail to adequately replicate real brace geometry. [PERSON] et al. [13] presented a more accurate model, but the results of FEM analysis pertained solely to the narrow problem of topological optimisation of the design, without a detailed analysis of the distribution of stresses and deformations in the orthoses structure. Due to the nature of the structure, 3D modelling of the orthosis structure appears to be a challenging exercise.