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STUDY DESIGN: A retrospective study measuring postoperative serum titanium levels in patients with titanium alloy spinal instrumentation. OBJECTIVE: To determine serum titanium levels in patients after instrumented spinal arthrodesis with implants composed of titanium alloy and to identify potential factors responsible for any increase in ion levels. SUMMARY OF BACKGROUND DATA: Previous studies have documented localized metal debris in the tissues surrounding spinal instrumentation. Systemic distribution of metal debris has also been demonstrated by measuring elevated serum metal ion levels in patients with titanium spinal implants; however, no studies exist on the impact of instrumentation characteristics on serum ion levels. METHODS: Serum titanium concentrations were measured in 30 patients with titanium spinal instrumentation at a mean 26 months after surgery and compared with a control group without metallic implants. Comparisons were made regarding serum titanium levels with respect to specific instrumentation characteristics such as number of pedicle screws used, and the presence of cross connectors or titanium interbody devices. RESULTS.: Serum titanium levels were significantly higher in patients with titanium spinal implants (mean, 2.6 microg/L) when compared with controls (mean, 0.71 microg/L). Subjects who underwent an instrumented arthrodesis of only one spinal segment had decreased serum titanium levels when compared with those who were fused at 2 or more spinal segments (mean, 2.3 vs. 3.1 microg/L) and patients with 4 or less pedicle screws also had decreased serum titanium levels when compared with constructs of 6 to 8 pedicle screws (mean, 2.3 vs. 3.35 microg/L); however, both of these findings were not statistically significant. Patients without cross connectors had a slightly increased serum titanium level when compared with those with connectors (mean, 2.7 vs. 2.44 microg/L); however, this finding was also not statistically significant. Patients with titanium interbody devices had a statistically significant elevation in serum titanium levels when compared with those without (mean, 3.3 vs. 1.98 microg/L). CONCLUSION: Significantly higher serum titanium concentrations were observed in subjects with titanium spinal instrumentation when compared with controls. Continued research is necessary to examine the relationship between Ti interbody devices and cross connectors with regards to serum ion levels.