PA8: METAL ION RELEASE IN PAEDIATRIC SCOLIOSIS INSTRUMENTATION

Abstract

Instrumented spinal arthrodesis is a common procedure to correct scoliosis. The long-term consequences of these retained implants is unclear. Concern of possible toxic effects of raised metal ion levels have been reported in arthroplasty literature. We investigated serum metal ion levels in patients having instrumented spinal arthrodesis for scoliosis correction.

The study included patients who underwent posterior spinal arthrodesis using Isola stainless steel instrumentation for scoliosis between 1998 and 2002. Patients having post-operative complications, instrumentation removed, revision surgery or additional in situ metal implants were excluded. Participants completed a questionnaire to evaluate exogenous chromium exposure.

Serum levels of chromium, molybdenum, iron and ferritin were measured in venous blood samples. Participants with elevated serum chromium levels underwent further erythrocyte chromium analysis. Comparisons were made with two control groups;

1. “non-instrumented” individuals with scoliosis and

2. “normal” unaffected volunteers. All control group participants underwent serum and erythrocyte analysis (as above).

Thirty “instrumented” patients (Group 1, 26 females and 4 males), 10 “non instrumented” patients with scoliosis (Group 2) and 10 unaffected volunteers (Group 3) were included in the study. Mean age at surgery was 13.8 years (range 6.6 to 13.2), mean time from surgery 5.7 years (range 3.4 to 8.1). Elevated serum chromium levels were demonstrated in 11/30 (37%) Group 1 participants. In the control groups, elevated serum chromium levels were demonstrated in 0/10 (0%) in Group 2 and 2/10 (20 %) in Group 3. There was a statistically significant (p=0.001) elevation in serum chromium levels between scoliosis participants with retained spinal implants, and those without.

There was no significant correlation found between Groups 1, 2 and 3 for serum molybdenum, iron and ferritin levels. Erythrocyte chromium measurements from all participants (n=31, 100%) were considered within the normal range.

At a multivariant level, the results of a stepwise censored regression (n=50) indicated the significant predictors of serum chromium to be spinal implants (p=0.001), gender (male versus female, p=0.04) and iron grading (low, normal or high, p=0.05).

Time since surgery was found not to have a significant correlation with chromium levels (p=0.147).

Raised serum chromium levels were detected in 37% of patients after instrumented spinal arthrodesis for scoliosis correction. This new finding has relatively unknown health implications but potential genotoxic, dysmorphic and carcinogenic sequelae; this is especially concerning with most scoliosis patients being adolescent females with their reproductive years ahead.