A study of data relating to 3404 hips enrolled in 18 comparative studies and over 830 000 operations in national registries showed limited evidence on comparative effectiveness of various hip implant bearing combinations according to a BMJ report published in November, which can be found here.
The report is entitled “Comparative assessment of implantable hip devices with different bearing surfaces: systematic appraisal of evidence” and authored by specialists associated with US FDA’s Center for Devices and Radiological Health (CDRH).
Clearly the eye is drawn to the metal-on-metal data following severe cases of metallosis related to the release of metal ions from the implants.
Metal-on-metal bearings are particularly attractive to surgeons as they allow use of larger femoral heads and supposedly reduce the risk of dislocation and improve the functional outcomes in younger patients. Their increased longevity is also attractive for this patient group. Consequently, as the report states, “They were quickly adopted by surgeons and often used even in older patients. In one study, one out of three older patients undergoing hip surgery received metal-on-metal hip implants.” Yet, as has been widely publicised, in August 2010 Johnson and Johnson recalled over 93 000 metal-on-metal (ASR) implants.
So what of the data? Well it appears that indicative figures suggest that disease-specific functional outcomes including general quality of life measures were no different between patients with metal-on-metal or ceramic-on-ceramic hip implants compared with traditional hip implants. However “There is some evidence of higher rates of revision surgery associated with metal-on-metal implants compared with metal-on-polyethylene implants”. These data were from the national registries of Australia, New Zealand and England & Wales, although three other smaller studies, including one US population (Center for Medicare and Medicaid Services) didn’t report such results.
According to the paper, “While one clinical study reported fewer dislocations associated with metal-on-metal implants, in the three largest national registries there was evidence of higher rates of implant revision associated with metal-on-metal implants compared with metal-on-polyethylene.”
The authors state that “the results do not indicate any advantage for metal-on-metal or ceramic-on-ceramic implants compared with traditional bearings. A large and high quality randomised controlled trial of bearing surfaces in total hip replacement needs to be conducted before any claims of benefit are made. Until then national registries provide important real world data that are critical for the safety and future comparative safety and effectiveness evaluation.”
So, after this massive data collection and analysis exercise, the conclusion is that there isn’t much in it.