I have a bump on the underside of the knuckle of my right ring finger (palm side). The bump is located right in the center of my knuckle and is rock hard (equally as hard as all of the bones in my hand). It is approximately the size of a pea and is not even the slightlest bit moveable. It is painful when pressure is applied to it. Does anyone have any idea as to what this could be? I work in a restaurant where i carry a lot of heavy plates, which dig into my hand. I also have nights which I have to spend hours polishing glasses and my hands end up hurting me just from the repetative movement and from edges digging into different areas of my hand. Could this have anything to do with what is going on with my knuckle? I would appreciate any information that you can give me. Thank you.

ps-I am 18 years old, so it is doubtful that the bump is arthritis related.