A chance discovery by academics in Nottingham has found that a simple optical illusion could unlock a drug-free treatment for arthritis.
The computer-generated mind trick has been tested on a small sample of sufferers and found that in 85 per cent of cases it halved their pain.
Research is still in the early stages, but initial results suggest the technology, called Mirage, could help patients improve mobility in their hands by reducing the amount of pain they experience.
For the illusion to work patients place their hand inside a box containing a camera, which then projects the image in realtime onto a screen in front of them.
The subject then sees their arthritic fingers being apparently stretched and shrunk by someone gently pushing and pulling from the other side of the box.
The Mirage mind trick has been developed by The University of Nottingham's Psychology department. It was first used at an open day last year as part of research project into the way our brains put together what we see and feel happening to our bodies.
The machine was a big hit with children at first, but it was one of their grandparents who made an unexpected discovery.
Dr Catherine Preston, from Nottingham Trent University, who is collaborating on the study said: "The grandmother wanted to have a go, but warned us to be gentle because of the arthritis in her fingers.
"We were giving her a practical demonstration of illusory finger stretching when she announced, 'My finger doesn't hurt any more', and asked whether she could take the machine home with her. We were just stunned - I don't know who was more surprised, her or us."
The chance find was followed up by recruiting 20 volunteers with osteoarthritis to put Mirage to the test.
The subjects averaged 70 years old and had all been clinically diagnosed with arthritic pain in their hands and fingers. Before starting the test they were asked to rate their pain from 0-20, with 0 indicating no pain and 20 representing the most unbearable pain they could imagine.
Pam Tegerdine, from Nottingham, volunteered for the first study. She has suffered with osteoarthritis since her 30s and now has constant pain in her hands, feet, and lower back.
Physiotherapy and numerous prescription drugs help, but she said the optical-illusion technology was like nothing she had ever experienced.
"It was a very weird sensation, but as my finger was being 'stretched' it felt more and more comfortable. I just wanted it to stay like that, to keep that image in my head. If this could lead to a drug-free treatment for arthritis then that would be fantastic."
The team were looking at how the illusion affected painful and non-painful parts of the hand when they were apparently stretched or shrunk. The study showed a marked reduction in pain - on average halving the discomfort for 85 per cent of volunteers.
Some reported greater reduction in pain for stretching, some for shrinking and some for both.
The pain reduction worked only when painful parts of the hand were "manipulated" and for a third of the volunteers it temporarily eliminated the pain altogether.
Anecdotally, many volunteers also reported an increased range of movement. The results will be reported in the next edition of the medical journal, Rheumatology.
Osteoarthritis is a debilitating and painful inflammatory condition that affects the joints, and is one of the most common arthritic conditions.
Around 10 million people suffer from some form of arthritis, the most at-risk being those over 50.
There is currently no cure, but the symptoms can be managed by a range of treatments including painkillers and physiotherapy. Doctors say pain can be a barrier to sufferers trying to exercise and keep joints mobile.
The Nottingham team hopes it can find a use for the new technologies in physiotherapy, allowing health professionals to reduce pain for sufferers while exercising their joints.
Eventually, cheaper technology may also allow a low-cost, smaller model of the system to be produced for sufferers to keep at home - offering brief periods of respite from their discomfort.
Dr Newport stressed that the work is at a very early stage and that further studies are needed to further assess Mirage and its effect on pain reduction.
Researchers have secured a £23,000 grant for the next test phase and say they could collaborate with colleagues at the Arthritis Research UK Pain Centre at The University of Nottingham to study the brain's role in mitigating pain in arthritis.
Dr Newport added: "This... is an excellent example of how fundamental research can often produce unexpected and significant results. In my early career I was lucky enough to receive internal funding to develop the technology which is unique to The University of Nottingham.
"Without that support we never would have unearthed this surprising and exciting result, which potentially could be extremely important to the millions of people who suffer from this painful and debilitating illness."
Professor Alan Silman, medical director of Arthritis Research UK, said: "Although this research is in the very early stages and further work needs to be done, it's clearly an area with a lot of future potential and one which we're also investigating.
"Current drug treatments to relieve the pain of osteoarthritis are unsatisfactory, and although exercise, weight loss and self-management help some sufferers, many more people struggle to find adequate, side-effect-free pain relief."