Evaluation of frictional wear in a follow-up screw-rod kinematic node in GGS transpedicular stabilization

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).