Impact of facet joints on biomechanical behavior of the vertebromotor segment L4–L5: a three-dimensional model of the intervertebral disc with ideal fluid

An under-researched potential cause of low back pain is the subject of a review. Pain in the lumbar spine is a disease that affects a large part of society and has a significant impact on the life quality and performance of the world's population. Determining the cause/source of pain at the level of segment L4–L5 in clinical practice is a difficult task, because not every specialist is able to distinguish facet joint subluxation from disc herni-ation. Literature analysis on modeling of the vertebromotor segment has shown that stud-ies do not focus on continuous modeling of facet joints. The research aim is to present the problem formulation of the vertebromotor segment L4–L5 taking into account the presence of fluid in the facet joints and to analyze the results of the model behavior. The mathematical formulation of a mixed form problem (a combination of elastic and ideal fluid problems) for the vertebromotor segment L4–L5 using Ansys is described. The cur-rent problem formulation models axial traumatic loading of the vertebromotor segment L4–L5 with subluxation of the facet joints, which is typical for drivers, tractor drivers and sportsmen. As an assumption, synovial fluid is assumed to be an ideal fluid. Modeling of the segment stress-strain state under a compressive axial load of 100 kg showed that the fluid pressure in the right and left facet joint capsules was 69.2 and 84.7 kPa, consequent-ly. The difference between the joint capsule pressures 18 % confirms that there is an asymmetrical distribution of axial compressive load in the segment and that the right joint capsule is compressed. This study highlights the need to consider the facet joints at the lumbar level when modeling the vertebromotor segment.