Tsao points to experiments where the mirror is covered as amputee subjects go through the motions of mimicking a normal limb; without sight to guide them, far fewer report a reduction in pain -- and some report that it actually makes the pain worse.
And interestingly, in a 2009 study performed by Tsao and colleagues at Walter Reed Military Hospital, they added a group of subjects who were asked to close their eyes and merely visualize moving their missing limb without the aid of a mirror. In this case, the number and length of the phantom limb pain episodes decreased by 100 percent in the group using the mirror, by 17 percent in the covered mirror group, and by 33 percent in the mental visualization group. When the patients in the mental visualization and covered mirror groups were switched over to the mirror method, they experienced significant decreases in pain too.
These studies suggest that the sensation of pain is caused by more than just the physical components of inflammation and swelling; it may be that conditions such as arthritis might improve without painkillers and conventional therapy. Besides phantom limb pain, mirror box has also been used successfully to treat complex pain syndromes and paralysis due to stroke.
Experts say visual-based treatments like mirror box and illusory manipulation may not be introduced into mainstream arthritis therapy for some time. However, considering no medications have been proven effective for changing the overall course of osteoarthritis, and interventions such as exercise and weight loss appear to offer only limited relief, it's seen as promising alternative for those for those who struggle with the pain and disability of the disease.