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Wear reduction of orthopaedic implants through Cryogenic Thermal Cycling
Christian Wight1, David-Michael Phillips2, Cari Whyne1
1Orthopaedic Biomechanics Laboratory, Holland Bone and Joint Program, Sunnybrook Research Institute, Canada; Institute of Biomedical Engineering, University of Toronto, Canada.
Background:
Material wear caused by relative micromotion of multi-part orthopaedic implants can impact physiology near the implant site and ultimately lead to revision surgery. Cryogenic Thermal Cycling (CTC) is a process that refines and stabilizes the crystal lattice structure of materials by introducing them to temperature modulation cycles that include extremely low temperatures. This method has been proven to significantly improve the performance and wear life capabilities of mechanical components in an efficient, sterile and non-polluting process. This technical note is aimed to evaluate the impact of CTC on wear resistance at head-neck taper connections used in total hip arthroplasty (THA).
Methods:
Mock up components (heads and trunnions) using the same materials representative of THA implants were manufactured for this study. Components were placed into a custom-designed cooling chamber in which they underwent CTC. Short-term Incremental Cyclic Fretting Corrosion (ICFC) testing was conducted on thermally cycled and control (untreated) components, subjected to a full simulated gait with periodically increasing incremental peak loads (modified BioPuls Dual Station ASTM Hip Simulator). Corrosion-related electrical activity was measured for samples with and without CTC. A long-term wear test was also conducted to evaluate corrosion and fretting under double peak compression loading (no rotation).
Results:
From the short-term tests, samples that underwent CTC showed a significantly reduced corrosion current at the maximum testing compression load of 3,300 N (p = 0.048). The elevated corrosion onset load seen in the treated components did not reach significance (p = 0.152) and no significant difference in the mean change in open circuit potential (OCP) was observed (p = 0.471). Longer-term wear testing found variable differences in CTC and control components with respect to damaged surface areas.
Conclusion:
CTC was shown to be a viable method to reduce short-term corrosion-related electrical activity in THA head-neck taper connections. While consistent differences were not seen in longer-term measures of corrosion, further study is warranted to evaluate the potential of CTC in the context of reducing wear in modular THA implants.
