Bony Metastatic Breast Cancer

Prior to Sentinnel Node and Axillary Node biopsies I did have a bone scan.  The scan detected arthritis in the neck and right foot.  My neck has been painful, but not constantly. How does the radiologist determine/differentiate which increased activities in the bones are arthritis and which are bony metastatic?  Especially in the lower neck where the bones are very intricate?
FYI - All other x-rays, MRIs did not show any signs of metastatic cancer and I had 2 nodes postive with a tumor approx. 2 cm.
Clear margins on the lumpectomy and the nodes were not attached to anything else.  ER/PR+, HER2 neg, and all other results from biopsy of lymph nodes were favorable.

[CCF-RN,MSN-rf]

Dear valpal:  This is oversimplified as it is more of a radiology question.  Essentially, differentiating between boney abnormalities has to do with the amount and pattern of uptake on the bone scan.