In Vivo Oxidation and Wear in Remelted Highly Cross-linked Polyethylene Liners Retrieved at a Minimum of 10 Years after Total Hip Arthroplasty.

ABSTRACT

BACKGROUND: With the decreasing age threshold for patients undergoing total hip arthroplasty (THA), there is an escalating demand for enhanced polyethylene durability. Although reports assessing wear in remelted highly cross-inked polyethylene (HXLPE) through radiographic imaging exist, a consensus regarding its oxidation level is lacking. This study investigated the wear, oxidation levels, and degradation of remelted HXLPE that was retrieved at least 10 years after THA. METHODS: Our analysis focused on seven cases of melted HXLPE liners retrieved ≥ 10 years after THA. All patients were women, who had an average age of 64 ± 6.5 years at the initial operation, and the mean postoperative period after THA was 12 years and 11 months ± 1 year and 5 months. The wear conditions were measured by matching the shape analysis data obtained from a coordinate-measuring machine with a spherical model. Fourier-transform infrared spectroscopy was used to study the oxidation of polyethylene, and the polyethylene structure was evaluated using scanning electron microscopy. RESULTS: Osteolysis was not observed in any case on X-rays, computed tomography, or intraoperative findings during revision surgery. The average oxidation index of the sliding surface under load was 0.31 ± 0.22 in the six cases calculated after hexane treatment, and 0.69 for one case without hexane treatment. In the six cases calculated after hexane treatment, the average oxidation index of the non-load-bearing sliding surface was 0.11 ± 0.20. Average wear values were 0.33 ± 0.11 mm at 45 degrees from the equatorial direction and 0.04 ± 0.07 mm in the opposite direction. The initial structure of the polyethylene was preserved at all sites with low oxidation levels; however, in one case with stem subsidence, morphological changes and a high oxidation index were observed. CONCLUSION: Long-term oxidation and wear of remelted HXLPE liners retrieved from THA patients were minimal.