Abstract
Aim
To assess the effect of different polyethylene modifications on Total Hip Replacement survival.
Methods
We combined the NJR dataset with polyethylene manufacturing properties as supplied by the manufacturers. Cause specific and overall reasons for revisions were analysed using Kaplan-Meier and multi-variate Cox proportional hazard regression survival analyses. Revision for aseptic loosening was the primary endpoint. Modification variables included resin type, radiation source, multiple cross-linking treatments, cross-linking dose, terminal sterilisation method, terminal sterilisation radiation dose, stabilisation treatment, total radiation dose, and packaging.
Results
A total of 292,920 primary THR cases were included with an associated 5,329 revisions. The variables found to significantly affect implant survival were the total radiation dose, liner face asymmetry, and stabilisation treatment. Total radiation dose was divided into four groups: G1 (no radiation); G2 (>0 Mrad and <5 Mrad); G3 (>5 Mrad and <10 Mrad), and G4 (>10 Mrad). The adjusted Cox Regression model with revision for aseptic loosening as the endpoint (G1 as reference) revealed a HR of 0.74 (0.64, 0.86) for G2, HR 0.36 (0.30, 0.43) for G3 and HR 0.38 (0.31, 0.47) for G4. In groups 3 and 4, stabilisation with vitamin E and heating above melting point performed best.
Conclusion
Irradiation of polyethylene with 5MRad or more was associated with a marked reduction in the risk of revision for aseptic loosening. Irradiation with higher doses was not associated with a further reduction at 12 years of follow up.
