Long-term polyethylene wear rates and clinical outcomes of oxidized zirconium femoral heads on highly cross-linked polyethylene in total hip arthroplasty

A randomized prospective double-blind trial comparing highly cross-linked with conventional polyethylene in total hip arthroplasty : results at a minimum follow-up of 20 years

Aims

Highly cross-linked polyethylene (XLPE) was developed in an attempt to address the problems of wear and osteolysis causing failure in patients who undergo total hip arthroplasty (THA). The aim of this study was to compare the rates of PE wear and revision, and the clinical outcomes of conventional polyethylene (CPE) and XLPE, in a prospective double-blind randomized controlled trial (RCT) with a minimum follow-up of 20 years.

Methods

A total of 122 patients were randomized to be treated with either a CPE (Enduron) or an XLPE liner (Marathon; both DePuy Synthes, USA). Other than the liners, identical components were used: a Duraloc 300 metal shell, a 28 mm diameter cobalt-chromium femoral head, and a cemented Charnley Elite femoral component. All patients were followed with anteroposterior (AP) and lateral radiographs at two days, six weeks, three and six months, and one, two, three, four, five, ten, and 20 years. PE wear was measured using PolyMig, which has a phantom validated accuracy of approximately 0.09 mm. The outcomes at ten years' follow-up in these patients have previously been reported.

Results

At a minimum follow-up of 20 years, 47 patients had died, five of whom had undergone a revision. Another 32 patients had undergone a revision and were alive, leaving 43 patients who had not undergone a revision and were alive (15 in the Enduron group and 28 in the Marathon group). No patients were lost to follow-up, but radiographs could not be obtained at final follow-up in two due to dementia, leaving 41 patients (15 in the Enduron group and 26 in the Marathon group) available for the measurement of PE wear. After the bedding-in period, the rate of wear was 0.181 mm/yr (95% CI 0.175 to 0.188) in the Enduron group and 0.034 mm/yr (95% CI 0.028 to 0.039) in the Marathon group. At 20-year follow-up, 37 patients had required revision. Those with CPE liners had a revision rate three times higher (28/37) than those with XLPE liners (9/37).

Conclusion

This is the longest-term RCT showing substantially improved clinical and radiological results when XLPE is used as the bearing surface in patients who undergo primary THA.

Highly Cross-Linked Polyethylene in Patients 50 Years of Age and Younger: A 20-year Follow-Up Analysis

BACKGROUND

Highly cross-linked polyethylene (HXLPE) has been an excellent bearing for total hip arthroplasty (THA) due to improved wear characteristics compared to conventional materials. Patients 50 years of age or younger are at high risk for wear-related complications of their THA, and few studies have followed these patients who have HXPLE into the third decade.

METHODS

In a retrospective review of 88 consecutive THAs performed in 77 patients aged 50 years and younger (mean 41; range, 20 to 50), in which HXLPE was utilized, they were evaluated for their clinical and radiographic results at an average of 20-year follow-up (range, 18 to 24). The current study reports on longer-term follow-up from our previously published series at shorter follow-up times. Patients were categorized by femoral head material: cobalt chrome (n = 14), ceramic (n = 30), and oxidized zirconium (n = 22) and by femoral head size: 26 mm (n = 12), 28 mm (n = 46), and 32 mm (n = 8). Harris Hip Scores were collected preoperatively and at the most recent follow-up. Radiographs were evaluated for linear and volumetric wear, radiolucent lines, and osteolysis.

RESULTS

Mean Harris Hip Scores improved from 47.1 (standard deviation [SD] 8.8) preoperatively to 92.0 (SD 7.7) (P < .0001) at 20-year follow-up. There was one hip that was revised for recurrent instability, and no hip demonstrated radiographic evidence of loosening or osteolysis. The mean polyethylene linear wear rate was 0.017 (SD 0.012) mm/y, and the mean polyethylene volumetric wear rate was 3.15 (SD 2.8) mm3/year, with no significant differences based on articulation type or head size.

CONCLUSIONS

Total hip arthroplasty with HXLPE in patients ≤ 50 years of age continues to demonstrate excellent long-term clinical and radiographic outcomes with low wear characteristics at 20-year follow-up, regardless of femoral head material or size.