Metal ion levels in patients with stainless steel spinal instrumentation

Study Design. Case-control study. Objectives. To determine whether metal ion concentrations are elevated in patients with spinal instrumentation. Summary of Background Data. Studies have shown that serum and urinary levels of component metal ions are abnormally elevated in patients with total joint arthroplasties. Little is known of metal ion release and concentrations in patients with spinal instrumentation. Methods. The study group consisted of patients who had undergone spinal instrumentation for various spinal disorders with a variety of stainless steel implants, 5 to 25 years previously. A group of volunteers without metal implants were controls. All subjects were tested for serum nickel, blood chromium, and random urine chromium/creatinine ratio estimation. Results. The study group consisted of 32 patients with retained implants and 12 patients whose implants had been removed. There were 26 unmatched controls. There was no difference in serum nickel and blood chromium levels between all 3 groups. The mean urinary chromium/creatinine ratio for patients with implants and those with implants removed was significantly greater than controls ( P < 0.001). The difference between study subgroups was not significant ( P = 0.16). Of several patient and instrumentation variables, only the number of couplings approached significance for correlation with the urine chromium excretion ( P = 0.07). Conclusion. Spinal implants do not raise the levels of serum nickel and blood chromium. There is evidence that metal ions are released from spinal implants and excreted in urine. The excretion of chromium in patients with spinal implants was significantly greater than normal controls although lower where the implants have been removed. The findings are consistent with low-grade release of ions from implants with rapid clearance, thus maintaining normal serum levels. Levels of metal ions in the body fluids probably do not reach a level that causes late side-effect; hence, routine removal of the implants cannot be recommended.