I think I am with you here Diane,
Fractures are the obvious pathology. They don’t always have a history of trauma as even a coughing fit can cause a fracture if there is some underlying osteopenia.
Be on the lookout for metastatic deposits or pathological fractures.
We can see the cartilage part of the rib that is invisible on x-ray so look at the cost-chondral junction area as well as the joint between the rib and the sternum.
Keep an eye out for underlying lung pathology,
I have seen a few cases where an enlarged nerve is seen adjacent tot he inferior edge of the last rib,
There is also the attachments of the serrates anterior muscle slips to the ribs, the attachments of pec minor as well.
The internal oblique muscle origin as well as the intercostal muscles themselves can be considered.
In the end with these patients I rely on them being able to localise the pain and then refresh your anatomy for that particular rib and look carefully at the rib itself and associated muscle insertions / origins.
Steve