Fluid composition impacts standardized testing protocols in ultrahigh molecular weight polyethylene knee wear testing

Area of Science:

• Biomaterials Science
• Orthopedic Engineering
• Tribology

Background:

• Total knee replacement (TKR) wear is assessed gravimetrically in simulator studies.
• Lubricant composition aims to mimic in vivo conditions, with weight gain corrected via load soak testing.

Purpose of the Study:

• To investigate the effect of different testing lubricants on TKR wear and fluid absorption.
• To evaluate the consistency of wear simulation results across different institutions and conditions.

Main Methods:

• Ultrahigh molecular weight polyethylene tibial plateaus were tested against titanium condyles under ISO 14243-1 standards.
• Two distinct lubricants (Fluid A and Fluid B) with varying additives were used across multiple test runs and institutions.
• Load soak tests were performed to quantify fluid absorption.

Main Results:

• Significant variations in wear and load soak rates were observed between Fluid A and Fluid B.
• Wear rate decreased from 16.9 to 7.9 mg/million cycles when switching from Fluid A to Fluid B.
• Fluid absorption was substantially higher with Fluid B (31.6 mg) compared to Fluid A (6.1 mg) after 5 million cycles.

Conclusions:

• Testing lubricant composition, particularly additives, critically influences TKR wear simulation outcomes.
• Direct comparison of wear rates is only valid if identical testing conditions, including lubricant specifications, are employed.
• Standardization of lubricant formulations is essential for reliable and reproducible TKR wear testing.