Background: Crosslinked polyethylene (XLPE) liners used for primary THA have demonstrated lower wear rates than noncrosslinked, conventional polyethylene (CPE) liners through the first decade of clinical service. However, little high-quality evidence is currently available regarding the second decade performance of these implants and it remains uncertain whether the onset of osteolysis has simply been delayed or if the wear associated with XLPE liners will remain low enough that osteolysis will not occur. It is also unknown how the potential reductions in wear and osteolysis will influence long-term revision rates.
Questions/purposes: Do patients who underwent THA with XLPE liners demonstrate (1) a lower rate of revision for wear-related complications; (2) a reduced wear rate; and (3) a lower frequency of osteolysis compared with those with CPE liners?
Methods: Over an 18-month period from 1999 to 2000, 226 patients who had 236 primary THAs consented to participate in a randomized controlled trial conducted at one institution. To be eligible for intraoperative randomization, patients had to be implanted with a 28-mm cobalt-chrome alloy femoral head, a 4-mm lateralized liner, and the same cup and stem design. Six patients with six THAs were excluded intraoperatively because they did not receive study components for reasons unrelated to the liner material. The remaining 230 THAs among 220 patients were randomized to XLPE liners or CPE liners. The mean age at surgery was 62 ± 11 years and there were no differences in age, gender, or body mass index among the groups. There was no differential loss to followup between the study groups; among patients not known to be deceased or having undergone revision, minimum 14-year radiographic followup is available for 85 THAs including 46 with XLPE and 39 with CPE liners. Polyethylene wear was measured radiographically using Martell's Hip Analysis Suite and areas of osteolysis were evaluated before revision or at most recent followup. Revision rates at 15 years using reoperation for any reason and revision for wear or osteolysis were calculated using cumulative incidence considering patient death as a competing risk.
Results: The cumulative incidence of revision at 15 years using reoperation for wear-related complications as an endpoint was lower in the XLPE group than the CPE group (0%, 95% confidence interval [CI], 0%-0% versus 12%, 95% CI, 7%-19%; p < 0.001). Among unrevised THAs with minimum 14-year radiographic followup, the mean steady-state linear wear rate for THAs with XLPE liners was lower than the mean linear wear rate for the THAs with CPE liners (0.03 ± 0.05 versus 0.17 ± 0.09 mm/year; mean difference, 0.14; 95% CI, 0.11-0.17; p < 0.001). Osteolysis of any size was noted among 9% (four of 46) of the hips in the XLPE group and 46% (18 of 39) of the hips in the CPE group (odds ratio, 0.19; 95% CI, 0.07-0.51; p < 0.001).
Conclusions: This randomized study with followup into the second decade demonstrated reductions in revision, wear, and osteolysis associated with the use of XLPE. The low wear rates and absence of any mechanical failures among the XLPE liners at long-term followup affirm the durability of these components that did not incorporate antioxidants. Although osteolysis has not been eliminated, it occurs infrequently and has not caused any clinical problems to date.
Level of evidence: Level I, therapeutic study.