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Advanced Testing Protocols Simulate Failures and Validate Antioxidant Polyethylene in Ankle Implants
Journal article   Open access   Peer reviewed

Advanced Testing Protocols Simulate Failures and Validate Antioxidant Polyethylene in Ankle Implants

Ryan Siskey, Patrick Hall, Ruth Heckler, David Safranski, James Johnson and Ariel Palanca
Journal of orthopaedic research, v 44(1), e26103
Jan 2026
DOI: https://doi.org/10.1002/jor.26103
PMID: 40384049
url
https://doi.org/10.1002/jor.26103View
Published, Version of Record (VoR)CC BY V4.0,  Open

Abstract

Arthroplasty, Replacement, Ankle Humans Joint Prosthesis Materials Testing - methods Oxidation-Reduction Polyethylene Polyethylenes Prosthesis Failure Antioxidants
Total ankle replacement (TAR) has become an effective treatment for end-stage ankle osteoarthritis. Multiple factors, including patient characteristics, surgical technique, alignment, and bearing surfaces, influence TAR survivorship. Polyethylene (PE) fatigue is a key consideration in improving outcomes. This study establishes a novel, clinically relevant testing protocol incorporating varus-valgus rotation to simulate polyethylene fatigue failures observed in mobile-bearing total ankle replacements. Using this robust methodology, we evaluated the impact of oxidation and antioxidant stabilization on ultrahigh-molecular-weight polyethylene (UHMWPE) performance in a mobile bearing implant application. A six-degree-of-freedom simulator was used to iteratively adjust loading parameters (1500-3000 N, -4° to +8° flexion-extension, ±5° axial rotation, and ±3° or ±8° varus-valgus rotation at 37 ± 3°C in 20 g/L bovine serum) until clinically observed midline fractures were replicated. Oxidation levels were measured by Fourier-transform infrared spectroscopy per ASTM F2102. This validated loading protocol was then applied to conventional (25 kGy GUR 1020) and vitamin E-stabilized (75 kGy GUR 1020-E) UHMWPE inserts and tested to visible fracture or a 3-million-cycle runout. Post-test fractographic analysis identified crack initiation sites. Conventional aged UHMWPE demonstrated fatigue failure under varus-valgus rotation (OI = 2.59 ± 1.11) but no failure without rotation. Vitamin E-stabilized UHMWPE showed no fatigue failure after 3 million cycles, even under varus-valgus rotation (OI = 0.23 ± 0.02). Fractography revealed fractures originating at the trough and propagating with cyclic loading. Oxidation significantly reduces polyethylene fatigue life, and varus-valgus rotation exacerbates this effect in mobile bearing TAR implants. Antioxidant-stabilized UHMWPE showed promising resistance to fatigue and oxidation. These findings support the role of antioxidant stabilization in improving TAR performance, and the protocols developed here provide a framework for assessing the safety of alternative materials.

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