A recent study in the British Medical Journal (Comparative Assessment of Implantable Hip Devices With Different Bearing Surfaces. Systematic Appraisal of Evidence. Art Sedrakyan; Sharon-Lise T Normand; Stefan Dabic; Samantha Jacobs; Stephen Graves; Danica Marinac-Dabic) set out to ‘determine comparative safety and effectiveness of combinations of bearing surfaces of hip implants’. This was a large meta analysis which showed that there was no difference in the outcome of more advanced bearings such as metal-on-metal or ceramic-on-ceramic compared to more traditional bearings such as metal-on-polyethylene. The implication of this study is that there is no point in using more expensive materials when cheap and cheerful ones seem to perform just as well. Whilst this common sense approach appears at first glance to be quite compelling, it ignores the fact that conventional hip replacements wear out quite quickly when used in younger men and women. The authors stated that ‘none of the studies reported age specific or sex specific analyses, and none reported race or patients’ comorbidity, such as diabetes and obesity’. Unfortunately, these factors are very important when a surgeon decides which hip replacement should be used for a particular patient. One size does not fit all! We know that large diameter metal-on-metal hip replacements don’t work well, but there is some evidence that ceramic bearings are getting good results in younger patients. This is a rapidly growing and controversial area, and underlines the fact that we know less than we think about implants and their effects on the human body.