Liz,
A recent bone scan I had showed a small spot of concern, this was followed by an mri which showed the same as the bone scan but was inconclusive. I then had a pet/ct which was negative, the area is too small to biopsy so another mri is planned for the end of this month to note any changes.
I'm not sure if anything cancer related has to be of a certain size before being seen on the mri but agree your pain could well be sciatica.
I've also had ongoing joint pain in the past from arimidex so this too may be a factor?
Sorry I can't help more, but it appears many of us have varying degree's of bone/muscle pain since diagnosis and always think it's cancer!
I really hope your Dr's can give you some answers soon
