THOUSANDS of artificial knee joints are implanted each year in the UK without sound evidence of their long-term safety and effectiveness, it is claimed.

Experts called for better long-term monitoring of patients undergoing knee replacement so the data can be gathered.

Knee replacement is one of the most common procedures in developed countries and tens of thousands of the operations are carried out in the UK each year.

Since the first procedure was performed in 1968 the number of available implants has proliferated, but a team of British, Australian and Swedish experts said this has occurred "with little or no evidence of effectiveness or cost effectiveness".

Professor Andrew Carr, from Oxford University, said: "The regulatory framework for new implants varies worldwide but has been generally much less rigorous than for new drugs.

"Currently, proof of safety of implanted materials is all that is required prior to approval for clinical use, rather than evidence for clinical effectiveness.

"Widespread surveillance of existing implants is needed alongside the monitored introduction of new implant designs as part of well-conducted, large-scale randomised trials."

The experts spelled out their message in an online edition of The Lancet medical journal.

Relying on reports of "revision" procedures, replacing failed implants, underestimates the scale of problems suffered by patients, they said.

Ageing populations, rising obesity rates and a larger number of younger patients raised the possibility of a rise in demand for knee surgery over the next two decades.

Mr Carr said: "Without high-quality, unbiased and reliable information, surgeons cannot make informed decisions on how to achieve the best outcome."

However, he stressed knee replacement surgery was still "one of the outstanding success stories of modern medicine".