The 2.7 mm and 3.5 mm screws included in various Acumed systems are composed of cobalt-chrome (CoCr) alloy and are used with Acumed plates consisting of titanium alloy and commercially pure titanium.
Dissimilar metals in contact in an electrolyte solution may initiate an electrochemical process known as galvanic corrosion, where one metal corrodes another as a result of an electropotential difference between the metals.2 Galvanic corrosion manifests as accelerated corrosion of the more active, corroding metal (anode), and slower corrosion of the more noble metal, if it corrodes at all.2
There is significant research on the safe use of CoCr and titanium in the body. Both CoCr and titanium are self-passivating, indicating that these materials tend not to have galvanic interactions over time.2 Kummer et al previously demonstrated that CoCr-titanium couples result in low, stable galvanic currents that gradually decrease over time.3 A number of orthopaedic device manufacturers are currently using CoCr screws and titanium plates in the same combination as Acumed.
In order to quantify the potential impact of galvanic corrosion on Acumed’s CoCr, third-party testing was completed. The corrosion rate and mass loss for each sample couple was determined and used to calculate material release.