I had inflamed cartilage of my ribcage when pregnant with kid #2
- it felt like my ribs were being ripped apart esp when 6 months along and kid kicked that direction.
Dr said aspirin/tylenol for a week or 2 and that fixed me up
but it didn't affect my arms at all.

Can you touch/press around the area ?
is it sensitive to external pressures or only internal
does breathing affect it? the movement of the ribcage?