Microbial Influenced Corrosion: A Novel Initiator of In Vivo Spine Rod Fracture

Spine rod catastrophic failure/rod fracture after implantation is estimated to occur in 10% of all cases worldwide with this rate remaining consistent for more than 20 years. To accommodate the spine mechanical environment, metal alloys such as austenitic stainless steels, cobalt chromium molybdenum alloys, and dual phase titanium alloys are used as they have a high resistance to fatigue failure. The work presented herein addresses the gap in understanding about what happens in a laboratory environment versus what is happening in human patients that results in metal leaching into tissues as well as a shortened lifespan of a spine rod in a patient population that is not capable of breaking these spine rods from purely mechanical means. Eighty-five (N=85) patients (51 female 62.9 {+/-} 13.5 years old, 34 male 62.7 {+/-} 10.9 years old) who had spine revision surgery due to patient mechanical issues, such as loss of sagittal or coronal balance, pain, pedicle screw loosening, hardware associated infection were included in this study. All explanted rods had optical indications of surface modification that were not the result of mechanical damage, e.g. gouges, scratches, notches. The presence of Ti6Al4V rods increases the presence of local tissue concentrations of elemental Ti (190.98 {+/-} 207.84 g/g (ppm)) in all patients over the amount that would normally be present in patients who never had any titanium based orthopedic device implants (spinous muscle, 13.12 {+/-} 11.43 g/g). PQS, HHQ, and NHQ ToF-SIMS molecular signals were found co-located to corrosion pits as well with AHLs and palmitic acids indicating microbial presence and metabolism in all patients. This suggests that MIC can cause in vivo pitting corrosion resulting on rod failure.