In vivo oxidation in retrieved highly crosslinked tibial inserts

Area of Science:

• Biomaterials Science
• Orthopedic Surgery
• Materials Engineering

Background:

• Ultra-high-molecular-weight polyethylene (UHMWPE) is a common bearing material in total knee arthroplasty.
• Highly crosslinked (HXL) UHMWPE offers improved wear resistance but its oxidation behavior requires further investigation.
• Understanding oxidation is crucial for predicting the long-term performance of HXL UHMWPE tibial inserts.

Purpose of the Study:

• To determine the in vivo or postexplant oxidation environment of retrieved HXL UHMWPE tibial inserts.
• To assess the influence of fabrication variables (irradiation source, dose) and post-irradiation thermal processing (annealing, remelting) on oxidation resistance.
• To test hypotheses regarding in vivo oxidation potential and differential oxidation rates between annealed and remelted HXL UHMWPE.

Main Methods:

• Analysis of 87 retrieved HXL UHMWPE tibial inserts using Fourier transform infrared spectroscopy.
• Quantification of oxidation and trans-vinylene index.
• Correlation of oxidation measurements with in vivo time, fabrication variables, and thermal processing.

Main Results:

• Subsurface oxidation was observed in 56% of retrieved HXL tibial inserts, correlating with in vivo time and thermal processing.
• Annealed HXL UHMWPE exhibited significantly higher articular oxidation rates compared to remelted UHMWPE (p < 0.001).
• Oxidation rates correlated positively with crosslinking irradiation dose and post-irradiation thermal processing.

Conclusions:

• In vivo oxidation of HXL UHMWPE tibial inserts is a significant concern, particularly for annealed implants.
• Fabrication and thermal processing methods critically influence UHMWPE oxidation resistance.
• Oxidation-induced loss of toughness in UHMWPE may contribute to fatigue damage in retrieved tibial inserts, with potential clinical implications.