Effect of mixing dissimilar metals on serum metal ion levels following spinal deformity surgery.

Abstract

Purpose: The increased use of hybrid spinal implants combining dissimilar metals raises concerns for galvanic corrosion, which can affect metal ion release and implant longevity. This study examines the variation in post-fusion metal ion concentrations among different hybrid implant constructs.

Methods: In this prospective multicenter observational study, patients undergoing elective surgery for idiopathic or neuromuscular scoliosis received either cobalt-chromium (CoCr/Ti) or stainless steel (SS/Ti) rods with titanium screw implants. Blood metal ion concentrations were measured preoperatively and at 3, 12 and 24 months. Longitudinal data were analyzed using linear mixed-effects models adjusted for repeated measures.

Results: A total of 37 patients were enrolled in the CoCr/Ti group and 35 in the SS/Ti group, with a majority of females (68% in CoCr/Ti vs. 71% in SS/Ti). There were no significant differences between the groups in age, BMI, number of rod attachments or rod surface area. Chromium (Cr) levels initially increased then plateaued, remaining consistently higher in the SS/Ti group, and significantly above baseline at 24 months. Cobalt (Co) concentrations also initially increased in both groups, but were higher in CoCr/Ti. Titanium (Ti) levels increased in both groups but continued to show a positive trajectory in CoCr/Ti at 24 months. Higher titanium concentrations also correlated with the number of rod attachments and instrument-related complications in CoCr/Ti but not the SS/Ti group.

Conclusions: With consideration of the different material properties in hybrid implant components, our findings suggest that differences in surface hardness appear to be more pertinent to metallic wear than galvanic corrosion.