RESUMO
Ten in-vivo failed spinal instrumentation systems, i.e. six Harrington distraction rods with sublaminar hooks, one Harrington distraction rod with segmental wiring and three Luque rods with sublaminar wires, were fractographically analysed. In both Harrington and Luque rods corrosion fatigue was the predominant mechanism resulting in the failure. Five Harrington rods fractured at the first ratchet junction; fractures of the Luque rods were initiated by fretting of sublaminar wire with the rod surface in the presence of spinal non-union. Fretting and crevice corrosion were found to play an important role in compromising the segmental spinal instrumentation. The susceptibility of the 316 L CW austenitic stainless steel to pitting and relative resistance to crevice corrosion were measured by cyclic anodic polarization tests. The oxide inclusions have been found to play a significant role in the pitting of the alloy.
