Hard swelling on carpus

Navi's left arm has developed a lump or some swelling right above the carpal bone that is hard, doesn't move when you push on it and it's NOT painful.

Several months ago after a walk she had the same swelling accompanied by a mild limp that lasted that evening and was gone by the next day. The swelling went away pretty quickly. It came back a few days ago and was double the size that it is in this photo, but this time she didn't have a limp and isn't in any kind of pain at all. The next day it has gone down to this size and hasn't changed since.

What might it be?

hjkk by sk Ki, on Flickr

If my dog had something like that I'd be at the vet for xrays as soon as possible. Osteosarcoma can present that way (and in that spot) in the beginning and it would freak me the **** out. That said, I hope that's NOT the case and it's something simple and nothing to worry about! Since it's been there so long (assuming this is the same thing as last time, just coming back), I would say osteosarcoma is less likely. VIBES coming your way!

I certainly hope it's nothing that serious! I've told my friend to bring her in to get it checked out when he gets home juuuust in case - they're off on a beach vacation together on the island right now (lucky dogs). Thankfully she falls into the less likely candidate category when it comes to osteosarcoma, but you never know, she could still get it.

Our dog had sesamoiditis when she was younger and it looked similar. Have you looked into that at all? It was about five years ago that she had it so I don't really remember too much about it.

I hope it's nothing too serious!