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Introduction The understanding of the biomechanics of movements in the spinopelvic segment plays an important role in the successful treatment of patients with hip-spine syndrome. Analysis of the biomechanical processes occurring in the biokinematic chain of the spine–pelvis–hip during the transition from standing position to sitting position allows us to conclude that the acetabular axis of rotation of the pelvis in space is not the only one. Classical methods for measuring PI, PT, overhang S1 are applicable for patients in a standing position and use the hip joint as a starting point, since it is the point of rotation of the pelvis in space in a standing position. Previously, using mathematical modeling, we described spatial changes in the pelvis during a given change in the body position and showed the presence of a second point of pelvis rotation in space, which appears in a sitting position. We assumed that in a sitting position, it is necessary to use other methods for calculating indicators of spinopelvic relationships for their determination. Purpose of the study was to evaluate the parameters of patients’ sagittal balance using the proposed alternative method in standing and sitting positions. Materials and methods Medical documentation and the results of X-ray examination of 20 patients with unilateral idiopathic coxarthrosis who underwent total hip replacement surgery were analyzed. The radiographic parameters were calculated: PI, PT, overhang S1 in standing and sitting positions, anterior inclination of the acetabular component; parameters PI ischial, PT ischial, deviation of the ischial tuberosities in standing and sitting positions were proposed and calculated. Results The study shows that there is no statistical difference in the values of the angles PI standard for a standing position and PI ischial for a sitting position. It corresponds to objective data and is generally accepted. Examples of changes in radiographic parameters of the sacral slope and the deviation of the ischial tuberosities were shown reflecting the rotation of the pelvis in space through the second, ischial axis, that confirm the biaxial concept of pelvic rotation. Discussion The calculations demonstrated the possibility of using alternative indicators of spinopelvic relationships (PT, distance of overhang of the sacrum (overhang S1), deviation of the ischial tuberosities). They enabled assessment of the spatial transformation of the pelvis and the ability to predict the spatial position of the acetabulum, which is an important factor for successful treatment of patients with combined pathology of the hip joint and spine. Conclusion Our findings complement the biaxial concept of pelvic rotation. An alternative method for measuring sagittal balance parameters in a sitting position has been proposed. Further research is required to assess the practical significance of this method.