Effect of Physiological Loading on Fretting Corrosion of Zimmer® Trabecular Metal™ Coupled Tibial Cones Interacting with Tibial Baseplates

Abstract

Aim: To evaluate possible micromotion between the existing design of the Zimmer® NexGen® Legacy Constrained Condylar Knee (LCCK) tibial baseplates and the Zimmer NexGen Trabecular Metal™ (TM) tibial augments, as well as with newly designed Zimmer NexGen LCCK TM coupled tibial cone augments. Study Design: Fretting corrosion testing, in a simulated accelerated corrosion laboratory environment, of the TM tibial half-augment (control sample) was conducted to provide a baseline for possible micromotion and subsequent debris generation between TM augments and tibial baseplates. Identical methodology was applied to the newly designed TM coupled tibial cone augments. Samples were disassembled after load testing. Qualitative visual inspection was used to evaluate the amount of fretting and corrosion (ranked on a 0-4 scale with 0 being no observed corrosion and 4 being the most extensive/severe corrosion). Place and Duration of Study: Zimmer, Warsaw, IN. April 4-20, 2012. Methodology: Testing was conducted on 2-axis servo-hydraulic test machines at 10 Hz. The entire tibial component was continuously immersed in 0.9% NaCl solution while 10 million cycles (Mc) of loading was applied. The selected test loads were based on the average patient body weight (BW) for the selected implant size and elevated by a factor of 1.7. Five samples were evaluated for each test group. All samples were visually inspected without magnification and under a microscope at 17x. Ranking was performed for the extent/severity of both abrasion and corrosion for both the control and new design groups. Results: After 10 million cycles of fretting corrosion testing, the ranking evaluation of almost no abrasion and no observable corrosion or debris is consistent with a stable fixation mechanism under aggressive loading conditions. Conclusion: Newly designed TM coupled tibial cones will not create a new risk of potential micromotion between the TM component and the tibial baseplate in a clinical situation.