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

Abstract

Summary: This was a prospective collection of metallosis and magnetically controlled growing rods (MCGRs) of 10 patients undergoing rod exchange. Titanium (Ti), Vanadium (V) and Neodymium (Nd) concentrations were increased. Black particles were present within the macrophages in the fibrotic tissues. Hypothesis: For metallosis in MCGR surgery, we hypothesize that Nd should also be present in the soft tissues in addition to Ti and V. We expect a chronic inflammatory response with phagocytic foreign particles in immune cells. Introduction: MCGRs have revolutionized surgery for early onset scoliosis. Complications especially metallosis (Fig. 1) is concerning as pseudo-capsule formations with black/grey particles are found. This study systematically investigates metallosis to reveal complete metal particle profile of the tissues surrounding the rod and the phagocytic immune response. 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. Results: Ten patients were recruited. Ti, V and ND concentrations in the biopsies taken near the wear marks were found to be significantly higher than those in the control tissue samples (Fig. 2). 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 (Fig. 3). 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 distraction sessions. Phagocytotic immune cells with black particles inside raise cautions of the long-term implications of metallosis.