NICE (National Institute for Clinical Excellence), a British governmental authority for assessment of treatment methods, recommended the modern metal on metal resurfacing operation for young patients with " advanced hip disease".
The NICE's Guidance document found, however, flaws in the only four papers published on this operation method. The Guidance document also recommends that the patients should be informed about all risks and benefits associated with this operation method. In a cautious tone the document says that "less is known about the safety and reliability" of surface replacement devices than about conventional total hip prosthesis.
To calm the patients who already have had a total hip surgery, the document says: "If you have already had a THR, do not worry. This guidance does not mean that your hip joint is not safe or should not have been used."
This is a remarkable statement because in the core of the document the Guidance says that there are no known reports comparing the efficacy of conventional total hip with the surface replacement operation method.
You may find the whole Guidance document on http://www.nice.org.uk/, reference N0102.