The aim of this experimental study was to analyze the impact of applying different configurations of the transpedicular fixation system on selected mechanical parameters of the thoracolumbar spine under conditions of its instability (after simulated fracture). Five study groups were tested: physiological, with compression fracture of the vertebra, with two-segment fixation, with three-segment fixation, and with four-segment fixation. Each of the analyzed study groups was subjected to axial compression, flexion, and extension. Based on the conducted experimental tests, the mechanical parameters, i.e., stiffness coefficient and dissipation energy, were determined for all groups under consideration. The stiffness value of two-segment fixation is significantly lower than the physiological value (during flexion and extension). The use of long-segment fixation considered in two configurations (three- and four-segment fixation) may result in excessive stiffness of the system due to the high stiffness values achieved (approx. 2530 higher than the physiological values in the case of compression and on average 60 higher in the case of flexion). The use of long-segment fixator design shows better results than short-segment fixation. Considering both biomechanical and clinical aspects, three-segment fixation seems to be a compromise solution as it saves the patient from more extensive stiffening of the spinal motion segments.

All segments of the spine are characterized by a corresponding curvature in the sagittal plane and different geometrical parameters of vertebrae, which affects the complicated structure of transition between subsequent segments. The aim of the study was to assess changes occurring in the thoracolumbar spine, as a result of application of the transpedicular fixation. The research was conducted on finite element model, which was constructed on the basis of CT images. Five different configurations of the model were analyzed: focusing on vertebral compression fractures and degeneration of intervertebral discs. The analysis showed that the highest displacement occurred for a segment with intervertebral disc degeneration. Transpedicular fixation of injured thoracolumbar spine is given the opportunity to improve the stability and stiffness of the segment under consideration.

The aim of the study was to assess the influence of the type of surface layer (passive vs. diamond-like carbon coated) and the angle of pedicle screw implantation on abrasive wear of sliding screw caps used in spinal growth guidance systems. The scope of the experiment included the performance of high-cycle mechanical tests using reciprocating motion, imitating friction processes that occur during the use of implants. Measurements and identification were also carried out of the type of wear generated by friction (tests of surface topography and changes in chemical composition). Examination of friction surfaces revealed all mechanisms of abrasive wear, i.e., microcutting, scratching, and furrowing. In the case of traditional locking caps, furrowing and scratching were most frequently observed, while for caps coated with diamond-like carbon (DLC), the dominant mechanism was scratching. For most of the friction nodes tested, those with a passive coating showed significantly greater wear than friction nodes with a DLC layer, regardless of the screw implantation angle. On one hand, the use of DLC coatings improves durability owing to increased resistance of the coated surfaces to abrasive wear, but on the other hand, it carries the risk of emergency wear when the DLC coating wears out.

Purpose The aim of this study was to evaluate the abrasive wear of the sliding screw-rod joint used in growth guidance system (GGS) stabilizers, allowing the translation of the screw along the rod during the spinal growth process in a standard and modified system. Methods The study used single kinematic screw-rod pairs made of titanium alloy Ti6Al4V. Mechanical tests (cyclic loads) simulated the stabilizer's operation under conditions similar to actual use. A microscopic evaluation was conducted, analyzing abrasive wear based on measured abrasion areas. Numerical simulations were performed for the standard joint system and for a structural change (an additional insert to increase contact area between the rod and sliding screw cap). Results The study evaluated the abrasive wear of the mating elements of the stabilizer. Mechanical tests showed an increase in the force observed (11.74±2.52 N) with the increasing number of load cycles. Microscopic evaluation showed abrasion of the caps and rods in two areas (upper and lower). Numerical simulations indicated the highest stresses in the standard system were on the mating elements, i.e., the rod and the cap (15.6 MPa). In the modified joint, stress distribution differed, concentrating on the surface of the insert and the rod, with maximum values of 6.0 MPa (PE insert) and 12.4 MPa (PEEK insert). Conclusions Comparing the stress distributions obtained in the numerical simulations and the abrasive wear effects produced in the mechanical tests, a similar mechanism was observed (the destruction of the top layer of the mating elements of the stabilizer).