Stainless steel wear debris of a scoliotic growth guidance system has little local and systemic effect in an animal model

Abstract

Options to treat early-onset scoliosis include guided-growth systems with sliding action between rods and pedicle screws. The wear was previously measured in an in vitro test, and in this in vivo rabbit model, we evaluated the local and systemic biological response to the stainless steel debris. Compared to the previous study, a relatively higher volume of representative wear particles with a median particle size of 0.84 μm were generated. Bolus dosages were injected into the epidural space at L4-L5 for a minimum of 36 rabbits across three treatment groups (negative control, 1.5 mg, and 4.0 mg) and two timepoints (12 and 24 weeks). Gross pathology evaluated distant organs and the injection site with a dorsal laminectomy to examine the epidural space and dosing site. Peri-implanted particle tissues were stained for immunohistochemical and quantitatively analyzed for IL-6 and TNF-α cytokines. Based on ISO 10993-6:2007 scoring, particles in the high-dose group were primarily non-irritant (12 weeks) with one slightly irritant. At 24 weeks, inflammatory cell infiltration was non-existent to minimal with all groups considered non-irritant at the injection site. Material characterization confirmed that particles detected in distant organs were stainless steel or contaminants. At 12 weeks, stainless steel groups demonstrated statistically increased amounts of cytokine levels compared to control but there was a statistical decrease for both at 24 weeks. These findings indicate that stainless steel wear debris, comparable to the expected usage from a simulated growth guidance system, had no discernible untoward biological effects locally and systemically in an animal model. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1980–1990, 2018.