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Bristol surgeons have started what they say is one of the most expensive trials of its kind to try to reduce long-term pain in joint replacement patients.

The £2.1m grant for the study at Southmead Hospital's orthopaedic unit will be carried out on 600 patients over the next five years.

Doctors are trying to see if giving a local anaesthetic during hip and knee replacements prevents chronic pain.

Prof Ashley Blom believes it could transform patient treatment worldwide.

The orthopaedic consultant, who is leading the team, said: ''Pain is quite poorly understood but we do think that you can become pain sensitised and people who have a lot of pain, their brain somehow changes the way it reacts to pain.

"And they have a more unpleasant experience in the long term.

"What we are hoping is the local (anaesthetic) will decrease the amount of pain they have at the time of the operation, which in itself is a good thing, and even better, if it can decrease the amount of pain people have in the long term and improve the outcome."

Half the patients on the trial will be given a local anaesthetic, and their experiences of pain following the operation will be compared with the rest of the group who are just given a general anaesthetic.

Barbara Ridding, 53, from Bristol, who is part of the trial, had a hip replacement five years ago and she said she was in pain for some time afterwards.

"I was frightened to death of moving and people touching me... I could not stop crying," she said.

The Bristol team say up to 10% of patients having hip replacements have long term moderate pain for the rest of their lives and they are trying to understand why.

Their theory is that reducing pain in the immediate aftermath of an operation for as little as 12 hours might prevent long-term discomfort.

The team are looking for more patients to take part in the trial.