Rod-Screw Constructs Composed of Dissimilar Metals Do Not Affect Complication Rates in Posterior Fusion Surgery Performed for Adult Spinal Deformity.

Abstract

This was a retrospective cohort study. The objective of this study was to compare implant-related complications between mixed-metal and same-metal rod-screw constructs in patients who underwent posterior fusion for adult spinal deformity. Contact between dissimilar metals is discouraged due to potential for galvanic corrosion, increasing the risk for metal toxicity, infection, and implant failure. In spine surgery, titanium (Ti) screws are most commonly used, but Ti rods are notch sensitive and likely more susceptible to fracture after contouring for deformity constructs. Cobalt chrome (CC) and stainless steel (SS) rods may be suitable alternatives. No studies have yet evaluated implant-related complications among mixed-metal constructs (SS or CC rods with Ti screws). Adults with spinal deformity who underwent at least 5-level thoracic and/or lumbar posterior fusion or 3-column osteotomy between January 2013 and May 2015 were reviewed, excluding neuromuscular deformity, tumor, acute trauma or infection. Implant-related complications included pseudarthrosis, proximal junctional kyphosis, hardware failure (rod fracture, screw pullout or haloing), symptomatic hardware, and infection. A total of 61 cases met inclusion criteria: 24 patients received Ti rods with Ti screws (Ti-Ti, 39%), 31 SS rods (SS-Ti, 51%), and 6 CC rods (CC-Ti, 9.8%). Median follow-up was 37-42 months for all groups. Because of the limited number of cases, the CC-Ti group was not included in statistical analyses. There were no differences between Ti-Ti and SS-Ti groups with regard to age, body mass index, or smokers. Implant-related complications did not differ between the Ti-Ti and SS-Ti groups (P=0.080). Among the Ti-Ti group, there were 15 implant-related complications (63%). In the SS-Ti group, there were 12 implant-related complications (39%). There were 3 implant-related complications in the CC-Ti group (50%). We found no evidence that combining Ti screws with SS rods increases the risk for implant-related complications.