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;

“non-instrumented” individuals with scoliosis and

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.

Introduction: Spinal arthrodesis with stainless steel implants is a common procedure to correct scoliosis however, the long-term consequences of retained implants is unclear. Raised serum metal ion levels have been widely published in arthroplasty literature with concern over possible toxic adverse effects associated with chronic exposure. We investigated serum metal ion levels in patients who had undergone instrumented spinal arthrodesis for scoliosis correction.

Methods: The study included patients who underwent posterior spinal arthrodesis using ISOLA instrumentation for scoliosis between 1998 and 2002. The minimal period of follow up was 3 years. Clinical information was available from a comprehensive Scoliosis Database, Department of Orthopaedic Surgery, Women’s and Children’ Hospital, Adelaide (WCH). Patients having post-operative complications, spinal instrumentation removed, revision surgery or additional in situ metal implants were excluded. Participants completed a questionnaire to evaluate exogenous chromium exposure. Blood samples were collected and processed by the WCH Core Laboratory. Serum levels of chromium, molybdenum, iron and ferritin were measured by Sydney South West Pathology Service. Participants with serum chromium levels outside the normal reference range underwent further analysis to evaluate chromium levels in erythrocyte haemolysate preparations (to assess the valency of abnormal chromium levels detected). Comparisons were made with two control groups; the first being individuals with scoliosis who had not undergone operative intervention and the other, “normal” unaffected volunteers. All control group participants underwent serum and erythrocyte analysis (as above). Ethics approval was obtained from the WCH Research Ethics Committee.

Results: Thirty patients (26 females and 4 males) who underwent instrumented scoliosis surgery, 10 non instrumented scoliosis patients and 10 unaffected volunteers were included in the study. Mean age of the operative group at surgery was 13.8 years (11.1–16.9) with a mean length of time from surgery of 5.8 years (3.5–8.2). In the study group, raised serum chromium levels were demonstrated in 11/30 (36.6%) of patients. Five of the 11 patients with raised chromium levels also had low levels of serum iron and/or ferritin. Erythrocyte levels of chromium were undetectable in all of the 11 (100%) patients. There did not appear to be an exogenous source of chromium exposure in any of these patients. In the non-operative control group with scoliosis, none had elevated serum chromium, iron or ferritin levels. 2/10 (20%) had high molybdenum levels. In the unaffected control group, 1/10 (10%) had raised serum chromium and molybdenum levels. Three control patients had low levels of serum iron and/or ferritin. All control participants, but one, had undetectable erythrocyte chromium levels. There was a significant difference in serum chromium levels between the study and control groups (p=0.01) with the group of patients who underwent instrumented scoliosis surgery having a greater proportion with high chromium and lower proportion with normal chromium.

Discussion: Raised serum chromium levels were detected in patients after instrumented spinal arthrodesis for scoliosis correction. This new finding in young patients has relatively unknown health implications but potential genotoxic and carcinogenic sequelae; this is especially concerning with most scoliosis patients being female and with their reproductive years ahead. These findings should prompt further research in this area, particularly to similarly investigate other spinal implant systems and assess the long term implications of raised chromium levels.