Scientists have demonstrated a cheap and simple therapy that uses an optical illusion to ease joint pain and stiffness in people with arthritis. The results of a small pilot study suggest the technique could help millions of people who experience the pain of inflamed joints without resorting to higher doses of painkillers and steroids, the most common drugs used to treat the condition.

The therapy draws on a technique called mirror visual therapy to convince patients' brains that their sore and stiff joints are pain-free and easy to move. The technique, which uses an optical illusion, has already proved extremely effective in relieving the pain that some amputees feel in their "phantom limbs".

To treat a person with an arthritic right hand, the patient first put their hand on the table in front of them. The researchers then positioned an upright mirror so that their forearm and hand were hidden behind it.

Next, one of the researchers stood behind the patient and put their own left hand down on the table. The patient could now see the researcher's hand and its reflection in the mirror.

The optical illusion occurred when the researcher opened and closed their left hand and asked the patient to mimic the movement with their hidden hand. When the patient looked into the mirror, they saw a reflection of the researcher's hand, but the brain took it to be their own. The visual trick seems to help the brain to reassess the hand as a healthy and pain-free part of the body.

In a preliminary trial presented as a poster at the Society for Neuroscience annual meeting in Washington DC on Sunday, eight patients with osteoarthritis and rheumatoid arthritis were given one minute of mirror therapy after ranking the pain in their joints on a 10-point scale.

On average, the patients ranked their pain one and a half points lower during the therapy, with some patients down-rating their pain by three points. The results have yet to be peer-reviewed.

"Our findings suggest that simple and inexpensive materials like mirrors could be used to reduce the pain and suffering caused by this common disease," said Laura Case at the University of California in San Diego. "Many patients reported a reduction in pain and stiffness during this illusion."

Arthritis affects more than nine million people in Britain. The more common form is osteoarthritis, caused by the steady wasting away of cartilage and eventually painful rubbing of bone on bone in joints. Rheumatoid arthritis is more severe and occurs when the immune system turns on the body and causes joint pain and swelling.

Candy McCabe, professor of nursing and pain sciences at the University of the West of England, has used mirror therapy to treat patients with persistent pain in their limbs. "You can get a lot of scepticism from patients and for that reason it doesn't work for everybody. It seems that the more you can believe in the illusion, the more your brain can be tricked into seeing something that it no longer has to perceive as painful," she said.

"Osteoarthritis is one of those conditions where over time we've recognised that what we thought was driving the pain in the problem joint probably plays less of a role than how the brain perceives that limb.

"The fact that they are doing these experiments in people with osteoarthritis and have shown good effects goes some way to confirming that osteoarthritis is more of a centrally driven problem, where the pain is more from the brain down rather than from the joints up."