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 muA/cm, respectively. Osteoblasts exposed to an EMF of 12.1 x 10 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.

Static electromagnetic fields generated by corrosion currents inhibit human osteoblast differentiation.

STUDY DESIGN: Human osteoblast cultures were exposed to a very low intensity static magnetic fields (SMF) to investigate its effects on osteoblast growth and differentiation. OBJECTIVE: Analysis of the effects of periprosthetic SMF on the growth and differentiation of human osteoblast cell cultures in vitro. SUMMARY OF BACKGROUND DATA: The effects of pulsed electromagnetic fields (PEMF) on cell proliferation, especially in human osteoblast-like cells is well described, whereas few data are available on the effects of SMF on osteoblast cell culture. We previously demonstrated that the proliferation of human osteoblast cultures is reduced when cells are exposed to a continuous low intensity SMF comparable to the one that occurs around metal devices (Ti spinal implant) because of the generation of electric currents between the screw (Ti6Al4V) and the rod (Ti). METHODS: Primary osteoblastic cells were isolated from a human femoral head. Osteoblast cultures were exposed to SMF and alkaline phosphatase activity was evaluated in the osteoblast cell cultures at different time points. Reverse transcriptase-polymerase chain reaction (RT-PCR) was performed to evaluate mRNA expression levels of osteocalcin, Runx2, and collagen I genes. RESULTS: The SMF-treated cells showed a progressive increase in the alkaline phosphatase activity which, however, remained always lower than the one observed in the control group at each observation time (72 hours, 7 and 14 days). RT-PCR demonstrated that Runx2 and collagen I mRNA were downregulated following SMF stimulation, whereas no change in osteocalcin mRNA was observed. CONCLUSION: Continuous low-intensity electromagnetic field comparable to the one that generates around metal devices because of the generation of corrosion currents inhibits osteoblasts differentiation pattern and might contribute at least in part to a decrease in periprosthetic bone formation occurring in vivo.