Metal Ion Release During Growth-Friendly Instrumentation for Early-Onset Scoliosis: A Preliminary Study

Abstract

Background: Metal ions released from spinal instruments can cause localized debris and distribute systemically to settle on distant organs. Children with early-onset deformities live with metallic implants for a substantial amount of time. No research focused on metal distribution in growth-friendly instrumentations. The aim of this study was to compare age-matched growing rod (GR) and magnetically controlled growing rod (MCGR) groups to noninstrumented controls.

Methods: The study was designed as a multicenter, prospective, cross-sectional case series. GR and MCGR applications of three institutions were included. A total of 52 children were enrolled. Blood samples were collected between December 2014 and February 2015. Biochemical serum analyses were performed to trace and quantify titanium, vanadium, aluminum, and boron. The GR group included 15 children. Mean age was 10.7 (range 6-15). MCGR group included 22 children. Mean age was 8.5 (range 2-13). Fifteen age-matched nonoperated children formed the control group. The mean age was 10.4 (range 5-15). One-way analysis of variance, Kruskal-Wallis, and Mann-Whitney U tests were used for comparisons.

Results: The mean serum titanium level in control, GR, and MCGR groups were 2.8 ± 1.4, 7.3 ± 4.3, and 10.2 ± 6.8 μg/L, respectively. GR and MCGR group titanium levels were higher than controls' (p = .008 and p < .001). The mean serum vanadium level in control, GR, and MCGR groups were 0.2 ± 0.0, 0.2 ± 0.0, and 0.5 ± 0.5 μg/L, respectively. MCGR group vanadium level was higher than control (p < .001) and GR groups (p = .004). Mean serum levels in control, GR, and MCGR groups were, respectively, 5.4 ± 4.1, 8.1 ± 7.4, and 7.8 ± 5.1 μg/L for aluminum and 86.7 ± 2.7, 86.9 ± 2.5, and 85.0 ± 6.6 μg/L for boron. The distribution of aluminum and boron were similar across groups (p = .675 and p = .396).

Conclusions: Both GR and MCGR applications significantly release titanium and possibly aluminum. MCGR further releases vanadium. MCGR possibly releases more titanium than traditional GR. Time-dependent alterations of serum ion levels, structural properties of the MCGR device, and exposure caused by magnetic distraction processes warrant investigation.

Keywords: Early onset scoliosis; Growing rods; Growth-friendly instrumentation; Magnetically controlled growing rods; Metal ion release; Titanium; Vanadium.