Bearing Materials in Hip Arthroplasty - What Do the Arthroplasty Registries Say?

In the early days of artificial joint replacement, the choice of bearing material was a decisive factor for the long-term success of an artificial joint. Through intensive research and development over more than three decades, the materials and their processing and sterilisation have been continuously improved. The materials used today all offer a high degree of safety and durability. As a result - In combination with the strict approval guidelines - the choice of a specific material is no longer as important as it was when artificial joint replacement was first introduced.This article focuses on the results of primary hip arthroplasty in eight established registries. In all of the registries examined, ceramic-ceramic bearings and bearings with cross-linked polyethylene cups or liners in combination with heads made of all common head materials, show very good long-term results with a low revision risk. The choice of head size varies considerably in the individual registries. In America, large (36 mm diameter) or very large ceramic heads (over 36 mm) tend to be used, even though the country's own registry warns against very large heads. In Australia, also mainly large heads are used. However, recent analyses indicate that large heads (36 mm) have a higher risk of revision in the long term. In Scandinavian countries, the Netherlands, and New Zealand, smaller heads (32 mm diameter) tend to be predominantly used. The situation in the other countries whose registries were analysed lies somewhere in between, with each country having its own special features. In England, the results of surface replacement are being closely monitored. The results are inconspicuous for the recommended patient population. The further performance of the newly introduced ceramic surface replacement is being followed with great interest. In Germany, the proportion of heads with a diameter of 36 mm is growing continuously, which should be critically questioned when considering the results from Australia. Ceramic-ceramic bearings are being used less and less frequently, even though they perform similarly well overall to hard-soft bearings and even better in some settings. Switzerland is the only country where this bearing still accounts for more than 10 % of treatments. Sweden no longer differentiates between materials in its annual report, but instead provides a ranking of the 74 Swedish clinics in terms of revision risk. In the Netherlands, the 32 mm head diameter is still the most frequently chosen. The German registry has the highest granularity of all registries. The use of dual mobility systems in primary endoprosthetics varies greatly between registries.Despite the differences in head materials and diameters, the results for hip replacements using HXLPE or ceramic cup inlays, show a comparable overall survival rate of approximately 96 % to 98 % after 5 years. What is noteworthy is the approach taken by the Swedish mother of all endoprosthesis registries, which no longer reports results for the different bearing combinations or head sizes, but instead reports the individual results for each facility. The overall good results for all currently used bearing materials in combination with appropriate patient selection make this a comprehensible step. Consequently, the respective clinical care quality is becoming increasingly important.