Systematic investigation of metallosis associated with magnetically controlled growing rod implantation for early onset scoliosis

Abstract

Introduction: Magnetically controlled growing rods (MCGRs) have revolutionised surgery for early onset scoliosis. Complications especially metallosis is concerning as pseudo-capsule formations with black/grey particles are found. This study systematically investigates metallosis to reveal the complete metal particle profile of the tissues surrounding the rod and the phagocytic immune response. Materials and Methods: This was a prospective observational study of patients treated with MCGRs undergoing rod exchange. Metal-on-metal contact in the form of ring-like wear marks was found on the distracted portion of the piston immediately outside the barrel opening. Biopsies of paraspinal muscles and control tissue samples were taken. Spectrum analyses of the rod and biopsies were performed to reveal the metal components and concentrations. Histological analyses of the biopsies were performed with haematoxylin and eosin staining. Results: Ten patients were recruited. Titanium (Ti), Vanadium (V) and Neodymium (Nd) concentrations in the biopsies taken near the wear marks were found to be significantly higher than those in the control tissue samples. Significantly increased Nd concentrations were also found in the tissues near the barrel of the MCGR. Chronic inflammation was revealed by the histological studies with fibrosis and macrophages infiltration. Black particles were present within the macrophages in the fibrotic tissues. Discussion and Conclusion: Ti and V were generated mainly at the barrel opening due to metal-on-metal contact, whereas the Nd from the rotor of the MCGR is likely released from the barrel opening during distractions. Phagocytotic immune cells with black particles raise cautions of the long-term implications of metallosis.