Persistently Raised Serum Titanium Levels After Spinal Instrumentation in Children

Titanium nanoparticles released from orthopedic implants induce muscle fibrosis via activation of SNAI2

Titanium alloys represent the prevailing material employed in orthopedic implants, which are present in millions of patients worldwide. The prolonged presence of these implants in the human body has raised concerns about possible health effects. This study presents a comprehensive analysis of titanium implants and surrounding tissue samples obtained from patients who underwent revision surgery for therapeutic reasons. The surface of the implants exhibited nano-scale corrosion defects, and nanoparticles were deposited in adjacent samples. In addition, muscle in close proximity to the implant showed clear evidence of fibrotic proliferation, with titanium content in the muscle tissue increasing the closer it was to the implant. Transcriptomics analysis revealed SNAI2 upregulation and activation of PI3K/AKT signaling. In vivo rodent and zebrafish models validated that titanium implant or nanoparticles exposure provoked collagen deposition and disorganized muscle structure. Snai2 knockdown significantly reduced implant-associated fibrosis in both rodent and zebrafish models. Cellular experiments demonstrated that titanium dioxide nanoparticles (TiO2 NPs) induced fibrotic gene expression at sub-cytotoxic doses, whereas Snai2 knockdown significantly reduced TiO2 NPs-induced fibrotic gene expression. The in vivo and in vitro experiments collectively demonstrated that Snai2 plays a pivotal role in mediating titanium-induced fibrosis. Overall, these findings indicate a significant release of titanium nanoparticles from the implants into the surrounding tissues, resulting in muscular fibrosis, partially through Snai2-dependent signaling.

Is posterior vertebral arthrodesis at the end of the electromagnetic rod lengthening program necessary for all patients? Comparative analysis of sixty six patients who underwent definitive spinal arthrodesis and twenty four patients with in situ lengthening rods

PURPOSE

Magnetically controlled growing rods (MCGR) should be removed or changed at most two years after their implantation in the treatment of patients with early-onset scoliosis (EOS) (Safety notice July 2021). However, in the face of patients at high risk of intraoperative complications and relying on the principle of auto-fusion of the spine, some surgeons would prefer a more wait-and-see attitude. The aim of this study was to report on patients who did not undergo final fusion at the end of the lengthening program with MCGR and to compare them with those who did.

METHODS

This was a multicenter study with ten centres. We collected all graduate patients with EOS who had received MCGR between 2011 and 2022.

RESULTS

A total of 66 patients had final fusion at the end of the lengthening program and 24 patients kept MCGRs in situ. The mean total follow-up time was 66 months (range, 25.3-109), and the mean follow-up time after final lengthening was 24.9 months (range, 3-67.7). Regarding the main curve and thoracic height, there was no significant difference in the percentage of correction over the whole follow-up between the two groups (p = 0.099, p = 0.176) although there was a significant difference between the end of lengthening and the last follow-up (p < 0.001). After completion of the lengthening program, 18 patients who had final fusion developed 24 of the 26 recorded complications (92.3%).

CONCLUSION

Contrary to the manufacturer's published safety notice, not all patients systematically benefited from the removal of the MCGRs. Although arthrodesis significantly improved the scoliotic deformity, no significant difference was found in terms of radiographic outcome between patients who underwent spinal fusion and those who kept the MCGRs in situ.

The Evaluation of Serum Metal Ion Levels and Metallosis in Graduated Patients With Magnetically Controlled Growing Rods

BACKGROUND

Magnetically controlled growing rods (MCGR) aim to control curve progression while limiting surgical burden in children with early-onset scoliosis. Systemic and local distribution of metal debris has been documented in children with spinal implants. The aim of the study was to assess serum metal ion levels and local metal debris-related changes at the conclusion of MCGR treatment.

METHODS

Between February 2019 and September 2022, all patients who had a conversion to definitive fusion at the completion of MCGR treatment in our institution were invited to participate in this study. Consenting patients had serum metal ion levels drawn (titanium, cobalt, and chromium) and histologic analyses of peri-implant tissue samples.

RESULTS

We enrolled 24 children who underwent definitive fusion post-MCGR treatment for early-onset scoliosis. The average age at definitive fusion was 13.3 years (range: 11 to 17 y). The average length of MCGR treatment was 4.8 years (range: 1.5 to 6.8 y). At the end of the MCGR treatment, 23 (96%) patients had elevated serum metal ion levels. Mean serum titanium levels were 165.4 nmol/L (range: 30 to 390 nmol/L), mean serum cobalt levels were 4.6 nmol/L (range: 1.2 to 14 nmol/L), and mean serum chromium levels were 14 nmol/L (range: 2.4 to 30 nmol/L). Peri-implant soft tissue histologic analysis demonstrated local metal debris and foreign body reactions in all patients.

CONCLUSIONS

At the completion of MCGR treatment, the majority of patients demonstrate elevated serum metal ion levels and local metal debris-related peri-implant soft tissue changes. Although there is no current literature to suggest these findings are harmful, further research as to the clinical significance is required.

LEVEL OF EVIDENCE

Level IV.