Serum levels of nickel and chromium after instrumented posterior spinal arthrodesis.

STUDY DESIGN

Cross-sectional study of 37 patients to measure serum levels of nickel and chromium after posterior spinal arthrodesis using stainless steel implants.

OBJECTIVES

To investigate the relationship between factors such as age, gender, pain, time from surgery, length of arthrodesis, and level of arthrodesis to serum metal ion levels after instrumented spinal arthrodesis.

SUMMARY OF BACKGROUND DATA

Measurable levels of metal ions in the serum can be detected after the use of stainless steel implants. There is some evidence to suggest that long-term exposure can potentially be toxic. Posterior spinal arthrodesis with stainless steel implants is a common procedure to treat spinal deformity in the adolescent population; however, the extent of metal ion exposure after posterior spinal arthrodesis is unknown.

METHODS

Patients that underwent posterior instrumented spinal arthrodesis with more than 6 months follow-up were recruited for this study. Patients with altered neurologic function were excluded. Serum levels of nickel and chromium were measured using inductively coupled plasma mass spectrometry. Pain was assessed using the Oswestry questionnaire. Spine radiographs were used to look for evidence of pseudarthrosis. Forty-five patients were approached, and 37 agreed to the questionnaire and blood test. Ten patients were men and 27 were women. Mean age at surgery was 14 years with mean follow-up of 6 years. Statistical correlations between serum metal ion levels and age at surgery, time from surgery, gender, number of segments fused, spinal instrument interfaces, pain, and instrumentation type were assessed.

RESULTS

Abnormally high levels of nickel and chromium above normal levels (0.3 ng/mL for nickel, 0.15 ng/mL for chromium) could be detected in serum after posterior spinal arthrodesis using stainless steel implants. There was a significant inverse correlation between serum nickel (r = -0.61, P < 0.001) and chromium (r = -0.64, P < 0.001) levels and time from surgery. When patients were grouped based on lengths of time from surgery, 0 to 2 years (n = 7), 2 to 4 years (n = 11), and >4 years (n = 8), the mean +/- SD for nickel (ng/mL) was 3.8 +/- 2.6, 1.3 +/- 1.1, and 0.9 +/- 0.8, respectively. Analysis ofvariance revealed significant group differences (P =0.004). Similarly, the chromium levels were 2.7 +/- 2.7, 0.6 +/- 0.4, and 0.3 +/- 0.3, respectively (P = 0.018). Only time from surgery was a significant multivariate predictor of nickel and chromium serum levels. Pseudarthrosis was not seen in this cohort.

CONCLUSIONS

Elevated levels of nickel and chromium can be measured after posterior instrumented spinal arthrodesis. The levels diminish rapidly with time from surgery but still remained above normal levels 4 years after surgery. Long-term implication of this metal ion exposure is unknown and should be studied further.