The aim of the study is to develop a method for biomechanical studies of stresses that occur in the spine-endofixator system during and after surgery. In the course of the study, the magnitude of the curvature of the spine, the geometric parameters and mechanical properties of the structures and elements of the spineendofixator system, the direction of forces and the magnitude of the external impact of the metal structure are evaluated, which will allow us to justify the choice of the length of the transpedicular spinal system. Based on the created algorithm of the method for studying the state of the structures of the spine -endofixator system, it is possible to determine: 1at what magnitude of curvature it is possible to install the endofixator structure based only on neighboring vertebral bodies to preserve the integrity of the vertebrae; 2 -at what magnitude of deformation it is necessary to install a more extended structure for a full-fledged correction of congenital curvature, taking into account the emerging stresses in the vertebral-endofixator system. The developed method of studying the state of the bone structures of the lumbar spine and the endofixator during the reconstruction of the vertebral-motor segment in young children can be used as a personalized preoperative planning in order to determine the length of the metal structure during the correction of congenital spinal deformity and reduce the risk of postoperative complications (destabilization of the metal structure, fracture of the bone structures of the instrumented vertebrae).