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

Abstract

Aims To investigate metallosis in patients with magnetically controlled growing rods (MCGRs) and characterize the metal particle profile of the tissues surrounding the rod. Methods This was a prospective observational study of patients with early onset scoliosis (EOS) treated with MCGRs and undergoing rod exchange who were consecutively recruited between February 2019 and January 2020. Ten patients were recruited (mean age 12 years (SD 1.3); 2 M:8 F). The configurations of the MCGR were studied to reveal the distraction mechanisms, with crucial rod parts being the distractable piston rod and the magnetically driven rotor inside the barrel of the MCGR. Metal-on-metal contact in the form of ring-like wear marks on the piston was found on the distracted portion of the piston immediately outside the barrel opening (BO) through which the piston rod distracts. Biopsies of paraspinal muscles and control tissue samples were taken over and away from the wear marks, respectively. Spectral analyses of the rod alloy and biopsies were performed to reveal the metal constituents and concentrations. Histological analyses of the biopsies were performed with haematoxylin and eosin staining. Results 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 macrophage infiltration. Black particles were present within the macrophages in the fibrotic tissues. Conclusion Ti and V were generated mainly at the BO due to metal-on-metal contact, whereas the Nd from the rotor of the MCGR is likely released from the BO during distraction sessions. Phagocytotic immune cells with black particles inside raise concern regarding the long-term implications of metallosis. Cite this article: Bone Joint J 2020;102-B(10):1375–1383.

“Law of Temporary Diminishing Distraction Gains”: The Phenomenon of Temporary Diminished Distraction Lengths With Magnetically Controlled Growing Rods That Is Reverted With Rod Exchange

“… 32 , 33 However, this is only a postulation and the relationship between rod slippage and metallosis events require further study. 34 In cases of continuous rod slippage and reduced length gains despite spacing out distractions and positive height gain, earlier rod exchange before the rod is completely lengthened may be indicated. The MCGR is likely nonfunctional and lengthening to a full 48 mm is doubtful.…”

Titanium wear from magnetically controlled growing rods (MCGRs) for the treatment of spinal deformities in children

“…MCGRs consist of a biomedical titanium alloy (Ti-6Al-4V) 7 . Despite biological and mechanical compatibility of titanium, microscopic metal particles have been observed extensively within the rods 8 and in the surrounding tissue of the rods 7 , 9 – 11 . It has been suggested that titanium wear debris can locally lead to inflammatory reactions, osteolysis or implant loosening 11 – 13 .…”

“…Despite biological and mechanical compatibility of titanium, microscopic metal particles have been observed extensively within the rods 8 and in the surrounding tissue of the rods 7 , 9 – 11 . It has been suggested that titanium wear debris can locally lead to inflammatory reactions, osteolysis or implant loosening 11 – 13 . Additionally, it is thought that titanium particles enter the blood circulation and accumulate in other tissues and distant organs 14 .…”

Unexpected benefits of arthroplasty

“…The lessons we have learnt from the hip have now been extended to the spine, to limb-lengthening, and to the knee. [18][19][20] Another issue that has recently assumed great importance is the labelling of cobalt as a carcinogen. A recent regulatory hazard review by the European Chemicals Agency resulted in the classification of cobalt as a class 1B carcinogen (presumed to have carcinogenic potential for humans).…”