In-vivo oxidation of highly crosslinked polyethylene and effect on wear in total hip arthroplasty

Abstract

Introduction: Retrieval studies of highly crosslinked polyethylene (HXLPE) acetabular liners have demonstrated presence of in vivo oxidation which may result in loss of mechanical properties. Whether time-dependent in vivo oxidation affects the wear properties of HXLPE is still poorly understood with few studies examining this relationship. Methods: A total of 43 total hip arthroplasties (THAs) using a single brand of HXLPE liner (Marathon), cementless cup (Duraloc), and 28-mm hip ball were performed in 33 patients. Clinical outcomes were evaluated. Linear and volumetric wear were determined using the Martell method. Presence of osteolysis and acetabular abduction and version angles were also assessed. Results: Average age at time of operation was 41.1 (29-50 ± 6.8) years. Average duration of follow-up was 12.3 (range, 8-15) years. One patient underwent revision at 9.8 years after surgery for reasons unrelated to polyethylene wear. Overall, for the entire study period excluding creep, linear wear rate was 0.046 mm/year. Calculated wear rates during years 2-5, 5-10 and 5-15 after implantation were 0.0408 mm/year (0-0.165 ± 0.0439), 0.0437 mm/year (0-0.169 ± 0.0472) and 0.0549 mm/ year (0.0247-0.116 ± 0.0289), respectively, p=0.384. There was no evidence of osteolysis on latest postoperative radiographs. Conclusion: Wear rates were not found to vary significantly with the in vivo duration. This suggests that remelting is indeed an effective strategy in the removal of free radicals and thus, the mechanical properties of the liner are not compromised over time. In vivo duration is not a significant factor affecting rates of wear of remelted HXLPE used in THA. Clinical performance is excellent even at >10 years after surgery.