The biocompatibility of alumina matrix composites like BIOLOX^®delta has been proven clinically, in in-vitro studies and in in-vivo animal studies^6,7,8,9. BIOLOX^®delta particles do not stimulate inflammatory responses, do not cause DNA damage, nor oxidative stress in human cells in clinically relevant doses i.e. the material and its debris are neither cytotoxic nor genotoxic⁶. Furthermore, recent in-vitro studies and analyses of explants have demonstrated that bacterial adhesion on BIOLOX^® ceramic surfaces is reduced in comparison to other bearing materials. Studies also show a reduced biofilm formation on BIOLOX^® surfaces compared to metal and polymer surfaces^10,11.

The reasons for data showing women to have lower implant survival with metal-on-metal HRA remain obscure. A number of reasons have been postulated and some high-volume surgeons have shown better outcome survival in women than men. There is little doubt that the reasons are multifactorial, and it should be borne in mind that HRA was introduced to a large population concurrently with surgeon learning and wide indications for HRA being factors. Most HRA devices have fallen by the wayside during the demographic period with some performing very poorly more so than others and the BHR was for many of the early years forming a high volume of data. For many years this implant was only available in 4 mm size increments dictating a method of head size choice which consequently induced what is now recognized as undersizing in many cases. This will have led to greater difficulty for ideal placement and a strong possibility of neck impingement which is in turn associated with edge loading cup placement and increased metal ion release.

Thus, todays HRA geometry, sizing operative indications, and technique training is very different for which statistics will emerge in due course but needs to have a restart from about 10 years ago. There is little doubt however that removing metal ions will be of benefit for the technology. The articulating surfaces feature all the proven qualities of the BIOLOX^®delta ceramic material. The most important are the lowest wear rate of all bearing materials, no metal ions, minimal wear debris generation, no polyethylene particles, superior lubrication and extremely low friction as well as precisely defined clearances. Ceramic materials are highly resistant to corrosion. As a result, issues that can lead to elevated wear rates and a high risk of adverse reaction to metal debris in metal-on-metal implants are ruled out by using a ceramic-on-ceramic bearing.

A change from metal to BIOLOX^®delta was shown to maintain low wear under tests known to accelerate the wear rate of metal-on-metal. Wear tests simulating microseparation conditions in large diameter ceramic resurfacing bearings have reported low wear rates; 47 times lower than that reported for metal-on-metal bearings under these same adverse conditions: ‘The low wear rate and highly biocompatible nature of this ceramic potentially offers an advantage over current meta-on-metal hip resurfacing designs and may represent the next generation of resurfacing devices’⁵. While there is currently limited data on these two implant devices it is possible that the indications may be widened clinically for what has been a restricted group more recently with metal-on-metal resurfacing devices including inclusion for smaller patients and women. With the use of ceramic- on-ceramic bearings, HRA could once again become a realistic option for patients with good bone stock in hip arthroplasty.

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