Abnormal metal ion levels following spinal instrumentation surgery

Abstract

Background: The incidence of abnormal metal ion levels following spinal surgery has been inconsistent across various studies. Metal implants, commonly used in spinal surgeries, can release ions that may accumulate in the bloodstream, leading to potential adverse health effects. Therefore, a comprehensive meta-analysis is necessary to assess the levels of metal ions in patients after spinal surgery.

Methods: We performed a systematic review and meta-analysis to evaluate metal ion levels after spinal surgery. A thorough search was conducted across four databases (PubMed, Embase, Web of Science, and Cochrane Library) up to September 2024. Studies were included if they measured serum or whole blood levels of metals such as chromium, cobalt, titanium, nickel, aluminum, or other relevant ions in patients post-spinal surgery. Data were extracted and analyzed using random-effects models to account for variability between studies. Funnel plots and Egger's test were used to assess publication bias, and I² statistics were employed to measure heterogeneity. Sensitivity analyses of the included studies were conducted to ensure the robustness of the findings. The Newcastle-Ottawa Scale (NOS) was used for quality assessment, evaluating factors such as study selection, comparability, and outcome measurement.

Results: A total of thirty-one studies, comprising data from over 1,404 patients, met the inclusion criteria. Postoperative levels of chromium, titanium, cobalt, aluminum, and nickel were significantly elevated compared to preoperative levels. The pooled standardized mean difference (SMD) for chromium was 2.50 (95% CI 1.74-3.26), for titanium was 2.05 (95% CI 1.41-2.70), for cobalt was 2.28 (95% CI 1.24-3.32), for aluminum was 0.75 (95% CI 0.24-1.27), and for nickel was 1.41 (95% CI 0.03-2.79). Subgroup analyses revealed variations based on the type of surgery, with higher SMDs observed in degenerative spinal conditions compared to scoliosis and spinal deformity-related surgeries for most metals. Significant heterogeneity was observed among studies (I² > 70%), but no evidence of publication bias was detected. Sensitivity analyses confirmed the stability of the results.

Conclusion: This meta-analysis confirms a significant postoperative increase in metal ion levels, particularly for chromium, titanium, cobalt, aluminum, and nickel, in patients following spinal surgery. These elevated metal ion levels raise concerns about potential long-term health risks, underscoring the importance of postoperative monitoring. Given the high heterogeneity among studies, more robust and standardized research is needed to establish clear clinical thresholds for safe metal ion levels and to assess the long-term implications of these findings. Regular monitoring of metal ion concentrations in patients with spinal implants may be crucial for early detection and prevention of metal-related complications.

Keywords: Meta-analysis; Metal ion levels; Postoperative complications; Spinal surgery.

Fig. 1

Study selection process

Fig. 2

Forest plot of SMD in Chromium levels post-spinal surgery

Fig. 3

Forest plot of SMD in Titanium levels post-spinal surgery

Fig. 4

Forest plot of SMD in Cobalt ion levels post-spinal surgery

Fig. 5

Forest plot of SMD in Aluminum levels post-spinal surgery

Fig. 6

Forest plot of SMD in Nickel ion levels post-spinal surgery

Fig. 7

Funnel plots for publication bias assessment in the meta-analysis of metal ion levels post-spinal surgery

Fig. 8

Leave-one-out sensitivity analysis of the meta-analysis on metal ion levels post-spinal surgery