Thank you for looking into this.
What kind of dog is he?
How old is he?
When did this start?
Is he still painful?
Is he eating and drinking OK?
Urinating and defecating normally?
Is he on any other medication, besides the metacam?
Is he still on the metacam?
Is he on strict rest or is he still active?
Oh, I am so sorry to hear this. I do however, agree with the possible causes you were given for his condition. I am glad to know that he was not in pain. I am truly sorry for your loss.
I will post this as an info request so that you won't be asked to pay.