Influence of surface layer and screw angle on tribological wear of sliding pedicle screws used in a growth guidance system

Abstract

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.