Clinical performance of sequentially irradiated and annealed highly cross-linked polyethylene tibial bearings: A retrieval analysis of 439 devices

Abstract

Background: Ultra-high-molecular-weight polyethylene (UHMWPE) remains the bearing surface of choice in total knee arthroplasty (TKA), yet oxidation and wear can lead to failure. Highly crosslinked, sequentially annealed polyethylene (X3, Stryker) was designed to resist oxidation, but its long-term in vivo performance remains debated. Methods: We analysed 439 retrieved X3 tibial inserts (mean time in situ [TIS] 4.35 years; range 0-15.2). Surgeons provided patient and implant data at revision. Bearings underwent visual inspection, white banding assessment, Fourier transform infrared spectroscopy (FTIR; ketone index, KI), and small punch testing (SPT). Logistic regression evaluated associations between patient/implant factors and failure modes. Results: Pain (36.9%), infection (29.1%), and instability (26.4%) were the main revision reasons. Infection was associated with male sex and higher weight (p< 0.001, p = 0.04). Instability was more frequent in women (odds ratio [OR] 2.49; 95% CI 1.55-3.86; p< 0.001). Thirty-nine bearings fractured (10.1%); women had a markedly increased fracture risk (OR 4.94; 95% CI 1.9-12.7; p< 0.001). Longer TIS raised fracture odds by 32.1% per year (95% CI 19.8-45.7; p< 0.001). SPT showed progressive decline in work to failure, dropping below 200 mJ after approximately 7 years. KI rose with TIS (p< 0.001), and each additional year increased odds of visual oxidation by 66.8% (95% CI 49.3-86.3). Conclusion: Sequentially annealed, non-remelted UHMWPE (X3) shows progressive in vivo oxidation with mechanical deterioration after approximately 7 years. Fracture risk is significantly higher in women and with longer implantation time. Retrieval analysis can identify patient groups at risk for early polyethylene failure and inform strategies to reduce revision rates.