Linear Wear Rates of a Highly Cross-Linked Polyethylene Hip Liner

To help limit wear, newer polyethylene liners, such as the highly cross-linked polyethylene (HXLPE) liners, have been developed. These newer liners undergo an alternating irradiation process, resulting in a stronger, longer-lasting liner. The purpose of this study was to analyze the wear rates of patients who underwent THA and received a newer generation HXLPE acetabular insert. Specifically, we compared: 1) linear vector wear amount and 2) linear vector wear rates in patients as an overall cohort and by gender. We also assessed patient satisfaction outcomes comparing preoperative Harris Hip Scores (HHS) to seven-week, one-year, and three-year HHS scores.

A total of 23 patients who underwent total hip arthroplasty (THA) with direct superior approach by a fellowship-trained orthopaedic surgeon at a private practice institution were analyzed after receiving institutional review board approval. Patients had a minimum two-year follow up, with the mean follow up being four years (range, three to five years). All patients received a 36-mm ceramic femoral head with an HXLPE liner. 2D radiographic polyethylene wear analysis was performed using the Martell Hip Analysis Suite (HAS; University of Chicago, Illinois), which has been previously validated in the literature. Outcomes were assessed using Harris Hip Scores.

A five-year linear wear rate of 0.073 mm/year (range, 0 to 0.160 mm/year) and an overall mean linear wear rate of 0.096 mm/year (range, 0 to 0.277 mm/year) were found. No significant differences in wear were seen between genders. Additionally, patients reported significantly better results at seven-weeks (83 points [range, 59 to 100 points]) and one-year (94 points [range, 85 to 100 points]) than preoperative (52 points [range, 34 to 73 points]) HSS scores (p<0.05). No patients underwent revision THA.

The results from this study highlight the benefits of using an HXLPE polyethylene liner in THA patients and further validates previously reported wear rates of HXLPE liners. After an early "wear in" period during the first year, the wear rates steadily decreased over time. This liner showed excellent early outcomes as no patients underwent revision THA. Furthermore, even as early as seven postoperative weeks, patients reported significantly better HHS scores. Future studies should track the same patient cohort over time to help develop a wear-rate prediction model.