A great fighter against the iconoclasts, St. John Damascene (ca 676-March 27 754-87), was accused of being an enemy of the state in which he lived, and as punishment, the Caliph ordered that one of his hands be chopped off. Afterwards, St. John took the severed hand, prayed in front of the icon of the Theotokos and fell asleep after a while. When he awoke, he found that his hand was healed. In honor of that healing, he made a hand of silver and added it to the icon. The altered icon has been duplicated ever since. You can see the silver third hand in the lower left of the icon.