The situation is very different with so-called “hard-on-hard bearings.” This describes hip joints in which both the head and the socket consist of a hard material: ceramic on ceramic, metal on metal, or even ceramic on metal. These joints produce so little abrasion that they will not even attain the weekly generated wear of polyethylene joints after 10 years of loading!
As everything else, these joints were, however, not without problems. Over the past few years, metal on metal has not met the expectations that were based on the biomechanical tests. Metal reactions that have not yet fully explained even today occurred relatively frequently. This particularly affected the large-head metal joints and some even had to be taken off the market. As a result, we have not been using metal-on-metal joints since several years.
Plastics have progressed in the meantime. In particular, the highly cross-linked polyethylene sockets show much less abrasion than the old plastics and because of this can tolerate much more stress.
Ceramic on ceramic as a brittle, amorphous material can break. Although this is very rare (about 1 in 10,000), when it happens, mostly to the ceramic part of the socket called the inlay – it must be exchanged. A positive aspect of ceramic is that the material is very wear-proof and mostly biologically inert. This means allergic reactions are not to be expected.
For young and active patients, we primarily use ceramic on ceramic today. With such a composite joint, almost unlimited physical exercise is possible and the patient need not worry about the number of steps they take.
