Fretting-corrosion in Hip Implant Modular Junctions: New Experimental Set-up and Initial Outcome

Area of Science:

• Biomaterials Science
• Mechanical Engineering
• Tribocorrosion

Background:

• Modern hip prostheses utilize modular designs with tapered junctions, introducing interfaces prone to fretting corrosion and micromotion complications.
• Understanding the mechanical and electrochemical behavior of these interfaces under simulated physiological conditions is crucial for improving implant longevity.

Purpose of the Study:

• To develop a novel fretting corrosion apparatus capable of characterizing the mechanical and electrochemical behavior of metal alloy couples used in hip prostheses.
• To evaluate the performance of different material combinations (Ti6Al4V-Ti6Al4V-Ti6Al4V, Ti6Al4V-Ti6Al4V-CoCrMo, CoCrMo-Ti6Al4V-CoCrMo) under simulated fretting conditions.

Main Methods:

• A new fretting corrosion apparatus was designed and validated for machine compliance and frictional interactions.
• Preliminary tests involved polished Ti6Al4V and wrought high-carbon CoCrMo alloy pins articulating against a Ti6Al4V rod in bovine calf serum at pH 3.0 and 7.6.
• Fretting motion was applied with a displacement amplitude of ±50μm at a normal force of 200N, while current and friction energy were monitored.

Main Results:

• Distinct, material-specific current evolutions and friction energies were observed, indicating unique degradation mechanisms for different alloy couples.
• Ti6Al4V-Ti6Al4V-Ti6Al4V couples exhibited earlier passivation and superior electrochemical behavior compared to couples involving CoCrMo.
• Current fluctuations, indicative of degradation mechanism transitions, were observed in Ti6Al4V-Ti6Al4V interfaces but not in Ti6Al4V-CoCrMo interfaces.

Conclusions:

• The developed fretting corrosion apparatus effectively characterizes the tribocorrosion behavior of hip prosthesis materials.
• Material combinations significantly influence the electrochemical and mechanical performance at modular junctions.
• Ti6Al4V-Ti6Al4V-Ti6Al4V junctions demonstrate better fretting corrosion resistance, suggesting potential for improved hip implant design by optimizing material pairings.