Models of L4 and L5 vertebrae, sacrum and iliac bones were constructed on the basis of a computer tomogram. The sacrum model was constructed with three types of fractures: outward from the facet joint passing through the facet joint and inward relative to the facet joint. In addition, two main splinters of the sacrum were modeled, as well as screws passing through the iliac bones and elements of transpedicular fixation. Two variants of typical loads were considered: compression load and bending moment, compression load and rotation moment. In the case where screws passing through the iliac bones were combined with transpedicular screws, the maximum displacement in the models (for all three types of fracture) significantly decreased. This allows us to conclude that the variant of fixation with the help of a transpedicular structure makes the model more stable, that is, increases the rigidity of the structure, preventing the fixed elements of the vertebral-pelvic complex from shifting relative to each other. Equivalent stresses in the screws passing through the iliac bones were also reduced when installing the transpedicular structure. In this case, the stresses in the bone tissues did not differ significantly with different types of implants and loading options. Thus, if we evaluate the field of equivalent stresses in the models, a more rational from the point of view of biomechanics is the option of installing a transpedicular system in addition to screws passing through the iliac bones. This will reduce the risk of damage to both the structure and bone tissue.
Surgical methods form the basis of modern approach to forefoot deformities correction. Scientific and practical interest in this topic is based on the patients’ growing need for specialized care, which is required by 64% of women and 25% of men. In most cases, there is bilateral deformation of both feet. Some scientists are strongly against simultaneous surgery on both feet. It is obvious that the solution regarding acceptability of the load in the early postoperative period requires quantitative individual assessment. This assessment can be performed using biomechanics. This paper presents the technique for assessing the bone-screw system when performing corrective osteotomies of the first metatarsal bone based on biomechanical methods. This technique allows to perform comparative analysis of various osteotomy methods for a particular patient. In this study we examined Chevron and Scarf osteotomy with displacement of bone fragments by 1/3 and 2/3 with different fixation variants. To solve this problem, personalized geometric models of the first metatarsal bone were built on the basis of computed tomography data using 3D Slicer and SolidWorks systems. The implant models were built as well. Finite element analysis was carried out using Ansys Workbench software. The focus of the study was to analyse stresses that occur on the plantar surface of the first metatarsal bone head during walking. Assessment of the maximum allowable shift of bone fragments for normalization of the forefoot deformities was carried out. The developed technique allows to choose osteotomy variant and justify the possibility of simultaneous surgery on both feet for a particular patient.