Structured Light Three-Dimensional Scanning Enables Quantification of Surface Corrosion on Retrieved Spine Rods from Revision Patients

Corrosion of titanium-based metals inside the human body has long been considered a potential health risk. There is an ever-increasing number of spine surgeries performed around the world, and a notable 9% to 45% reported reoperation rate due to spine implant (instrumentation) failure. Instrumentation failure in medicine is not a catastrophic breakage. It is when a patient can no longer biologically or physiologically tolerate the implant; thus, the instrumentation has failed in its function. Most spine reoperations (revisions) are due to a continued progression of spine degeneration or other conditions not associated with infection or breakage. This situation allows the study of how orthopedic implant alloys fare in the human body beyond mechanical failures. Optical inspection is a proven method for area quantification of metallic surface corrosion and wear. Spine instrumentation was retrieved during spine revision procedures under an institution-approved research protocol. Patients who never had any metal implants (n = 6) had an adjacent average Ti tissue concentration of 13.12 μg/g, while patients who had instrumentation (n = 20) had a significantly higher average Ti concentration of 113.73 μg/g. On a per-patient basis (n = 33), the average surface area corrosion was 45.14% while the overall average surface area wear was 6.00%. The presence of a clinically diagnosed infection had a slight but insignificant effect on the overall area of corrosion measured with an increase of corrosion of 38.54% for patients with a clinically diagnosed infection compared to 36.96% for patients with no diagnosed infection. While the 3D scanning with colometric measurements used herein cannot quantify pitting corrosion volume, when combined with gravimetric methods, it may yield a more robust understanding of human in vivo mechanisms of spine rod degradation. The presence of corrosion on all rods in comparison to in vitro studies showing minimal corrosion suggests that our understanding of the human in vivo corrosion environment is still extremely limited.