Periprosthetic electrochemical corrosion of titanium and titanium-based alloys as a cause of spinal fusion failure

Study Design. Posterior lumbar spine implants retrieved from patients affected by periprosthetic osteolysis were analyzed to identify corrosion and to investigate the electromagnetic fields (EMF) generated by corrosion currents and their effect on human osteoblasts proliferation. Objective. Analysis of retrieved instrumentation to better understand periprosthetic osteolysis and correlation of this information with clinical factors. Summary of Background Data. Recent studies have pointed out that mechanically assisted crevice corrosion represents the initial failure of spinal implants, resulting in the local decrease in pH, which leads to osteolysis. Methods. Electrochemical analysis was performed to characterize the corrosion currents and the EMF generated around the implants retrieved. Human primary osteoblasts cultures were used to determine the effect of continued EMF stimulation on cell growth. Cultures were exposed to the EMF stimulation for 48 hours, 72 hours, 7 days, and 14 days. Results. During the electrochemical corrosion tests both the screws and the bar showed a passivation current of 0312 and 0.05 mu A/cm(2), respectively. Osteoblasts exposed to an EMF of 12.1 x 10(-6) T displayed a decreased proliferation rate. At each observation time, there were differences in cell numbers between the unexposed cells and the exposed cells. Conclusion. Aseptic periprosthetic bone loss can be due in part to the generation of electric and electromagnetic phenomena generated around metal devices, which inhibit osteoblasts growth and might hamper periprosthetic bone formation. This mechanism is of clinical significance and should be more deeply evaluated.