The very first symptom I ever had was a very acute (but localised) pain in my lower ribs. I just thought it was a strained muscle and rode it out. Couldn't lie down for two weeks and had to sit in an arm chair each night. The pain subsided in two weeks.
A couple of years later after involvement of toes was more obvious a bone scan was ordered and to my surprise there was a hot spot where the rib pain had been. Because there are many muscles attaching to the ribs that enable breathing then it is not surprising that attachment site inflammtion (typical of spondylarthropathies) can occur at points on the rib cage.
If I knew then what I know now I would have used a strict NSD (which fortuneately works for me) and perhaps a short course of celebrex to get the inflammation and pain under control.

Dx Oct 2006 B27+ undifferentiated spondlyarthropathy (uSpA) with mild sebhorrhoeic dermatitis and mild Inflammatory Bowel Disease (IBD) controlled by NSD since 2007.