When things like that happen to me I think REAL hard and I realize I did something (lifted something, shoveled snow, did a new machine at the gym, ANYTHING) Sometimes it could be something you do everyday (ie: take a laundry basket up from the basement) and just step wrong or twist 2 degrees in the wrong direction. How long did you have the pain and how long did it take to get worse? If it's a metastasis then the original tumor would have to have been so bad you'd KNOW you had one somewhere else.
What kind of bone disease do you have? (it may have made you more susceptible to a strain from doing something)