Abstract
Purpose:
Crosslinking of polyethylene has become synonymous with longevity in total hip replacement. In the USA 70–85% of all polyethylene cups underwent crosslinking since 2008. Three publications appeared in the autumn 2011 volume of the “SA Orthopaedic Journal,” on the 10–33 year follow-up of the original SA crosslinked implant. The purpose of this study is to illustrate and confirm statistically, the improvement of the bone cement interface, provided that wear of polyethylene can be reduced to an absolute minimum.
Method:
Complete follow-up included Merle D'Aubigne clinical follow-up and radiological studies of the interface. Interpretation of radiological measurements was according to the D.M. (Digital Magnification) method, as published in 2007. This information was digitally analysed by the Department of Statistics, University of Pretoria. Follow-up was at six months post op and again at end of study. All cups were crosslinked with fixed-dose Gamma-rays, in a saturated acetylene environment, acting as mediating gas. This resulted in enhanced crosslinking in the superficial 300µ of the pre-manufactured implant.
Result:
Of the 97 cases studied, 58 showed no interface changes at all, while 26 cases had deteriorated moderately and of which only 7 cases needed revision as result of polyethylene wear of >1 mm. The correlation between wear and interface deterioration was statistically proven with excellent p-values. Most interesting was the third group of 16 cases (16.6%) that also showed no cup wear, but additionally displayed definite radiological signs of interface improvement.
Conclusion:
We conclude that the correlation between cup wear and interface deterioration is well proven and documented in this study. We can now state with confidence that polyethylene wear has to be minimised at all cost. Improvement of the interface is a new phenomenon which can only be achieved under extremely low wear conditions, and promises excellent longevity of the arthroplasty.
