In vitro studies of fretting corrosion of orthopaedic materials

Two models were used to study fretting corrosion of surgical alloys. In the first, the amount of load and motion between plates and screws was controlled, and corrosion rates of stainless steel and MP35N were determined by measurements of component weight loss and metal ion concentration in the test solutions. Stainless steel had the higher rate of fretting corrosion. The addition of 10% serum to saline resulted in a significant reduction of the corrosion rate of stainless steel and MP35N. The use of stainless steel screws in a mixed-metal combination with MP35N and titanium plates showed minimal effects on the performance of the stainless steel screws but an increase in fretting corrosion of the MP35N plates. In the second model, plates were applied to glass fiber-reinforced plastic tubes as bone analogues and subjected to cyclic axial loads. These results demonstrated a reduction in fretting corrosion rates associated with an increase in screw torque and a decrease in axial load. Corrosion rates were minimal with intact tubes simulating healed fractures and greatest with an oblique-cut fracture simulation. These models have proven useful for the evaluation of fretting corrosion rates of different alloys and for evaluation of variables such as fracture stability.