Metal concentrations in the blood and tissues after implantation of titanium growth guidance sliding instrumentation

BACKGROUND: Growth guidance sliding treatment devices such as Shilla (Medtronic, USA) or LSZ-4D (Conmet, Russia) used for the treatment of scoliosis in children who have high growth potential have unlocked fixtures allowing rods to slide during growth of the spine which avoids periodical extensions. However, the probability of clinical complications associated with metallosis after the implantation of such devices is poorly understood. The content of metal ions in the blood and tissues of pediatric patients treated for scoliosis using fusionless growth guidance sliding instrumentation, have not yet been investigated. PURPOSE: The aim of this study was to measure the content of metal ions in blood and tissues surrounding implanted growth guidance sliding LSZ-4D devices made of titanium alloy (Ti6Al4V) and to identify the incidence of metallosis associated clinical complications in some patients with these devices. STUDY DESIGN: One center case-control retrospective study. PATIENTS SAMPLE: Study group included 25 patients with high growth potential (3 males, 22 females, average age at primary surgery for scoliosis treatment is 11.4±1.2 years old) who had sliding growth guidance instrumentation LSZ-4D (Conmet, Moscow, Russia) implanted on 13 (range 10-16) spine levels for 6±2 years. The LSZ-4D device was made from titanium alloy Ti6Al4V and consisted of two rectangular section rods and fixture elements. Locked fixtures were used on one spinal level, while the others were unlocked (sliding). The control group consisted of 13 patients (12 females and 1 male, 11±1.2 years old) without any implanted devices. OUTCOME MEASURES: The content of Ti, Al and V metal ions in the whole blood and tissues around the implanted device was measured. Incidence of metallosis associated complications in the study group were recorded. METHODS: Metal ion content was measured by ICP-MC on quadrupolar Nexion 300D (Perkin Elmer, USA). RESULTS: 5 of 25 patients in the study group developed metallosis associated complications (two sinuses and three seromas in the lumbar part of the spine). Revisions were carried out in two of these patients. 90% of patients in the study group had increased content of Ti and V ions in the blood (2.8 and 4 times respectively). Median content of Ti ions in soft tissues adjacent to implanted sliding device was more than 1,500 fold higher compared with the control group. These levels are much higher than previously reported for spinal instrumentation. CONCLUSION: Increased content of Ti and V ions in the blood and especially in tissues around the titanium growth guidance sliding device LSZ-4D accompanied by clinical manifestations (seromas and sinuses) indicate the importance of improving of wear resistance of such instrumentation with the coatings and the necessity to exchange sliding instrumentation once the child is fully grown