Minimum 10-year outcomes of highly cross-linked polyethylene in total hip arthroplasty for hip dysplasia: Effect of cup inclination in a matched comparative study.

Abstract

Objectives: This study aims to compare the long-term outcome of highly cross-linked polyethylene (HXLPE) in hip dysplasia with osteonecrosis of the femoral head (ONFH) and evaluate the effect of cup inclination on HXLPE wear after total hip arthroplasty (THA) during a minimum 10-year follow-up.

Patients and methods: Between January 2000 and December 2012, a total of 124 patients who underwent primary THA for hip dysplasia or ONFH with a minimum 10-year follow-up were retrospectively analyzed. A total of 62 patients were successfully matched between the two groups (ONFH group, n = 62 and hip dysplasia group, n = 62). Primary outcomes included acetabular cup inclination, anteversion, and wear rates of HXLPE. Based on cup inclination, both groups were divided into three subgroups, classified as (1) ≤ 45°, (2) < 45° to < 50°, and (3) ≥ 55°. Secondary outcomes included the clinical score and radiographic findings of osteolysis, implant loosening, stress shielding, and heterotopic ossification. Kaplan-Meier curve and Cox regression test were used to compare the implant survivorship in the full cohort prior to exclusion and matching (178 hip dysplasia and 397 ONFH patients).

Results: There was no significant difference in survival rate without revision of prosthesis at 10-year between two groups (hip dysplasia: 94.7%, 95% confidence interval [CI]: 91.1% to 98.4% vs. ONFH: 95.7% (95% CI: 93.3% to 98.2%) (p = 0.4) Cup inclination was significantly steeper in the hip dysplasia group (47.6°, 95% CI: 46.0° to 49.3°) than in the ONFH group (43.9°, 95% CI: 42.3° to 45.5°) (p = 0.002). Steep cup inclination (> 55°) was significantly more frequent in the hip dysplasia group (11.3%, 7/62) than in the ONFH group (6.5%, 4/62; p = 0.006). However, wear rates of HXLPE were not significantly different between groups, and no correlation was found between cup inclination and HXLPE wear rate. No progressive osteolysis or prosthetic loosening was observed during follow-up.

Conclusion: Although patients with hip dysplasia demonstrated a steeper mean cup inclination and a higher incidence of steep cup positioning compared to those with ONFH, implant survivorship remained comparable between groups in the overall cohort. In the matched cohort analysis, HXLPE wear rates and clinical outcomes were also comparable between the groups. These findings suggest that, despite technical challenges in acetabular positioning, the use of HXLPE in THA for hip dysplasia provides satisfactory long-term performance and may alleviate concerns regarding cup inclination-related wear.