Analysis of friction and wear processes in an innovative spine stabilization system. Part 2. A study and model of the wear of a metal rod-polymer cord friction joint

Purpose: The purpose of this study was to model and describe the processes and phenomena occurring during the sliding interaction between biometal rods (titanium alloys Ti6Al4V and Ti6Al7Nb, austenitic steel AISI 316L, alloy CoCrMo) and PE-UHMW cords, used in spine stabilization systems to treat early-onset idiopathic scoliosis. Methods: The wear of friction joints in two lubricating solutions (acidic sodium lactate and distilled water) at stabilized temperature T = 38 C was studied. The wear of the polymeric cords was investigated through analyses of the chemical composition of the surface of the cords and microscopic examinations of the changes occurring on this surface. In addition, microscopic examinations and EDS analyses of the wear products filtered out from the lubricating medium were carried out. Results: Metallic particles were found to be present in both lubricating solutions at each stage of the friction process. The largest amount of metallic particles was recorded after 5000 motion cycles. Conclusions: The presence of metallic wear products is an evidence of the wear of the harder metal rod due to its friction against the PE-UHMW cord. This means that the use of guided-growth implants poses a risk of inflammations in the peri-implant tissues.