There are two areas of transition in our spine, one at the base of our rib cage and one at the top of it. They are called “transition” areas because they are where attachment of the ribs begin at the lower and upper borders of the rib cage.
These are often trouble spots because they are “transitions” from regions of comparatively less mobility to ones of comparatively more mobility. For example, in the low back, the lumbar region, where no ribs attach, is comparatively more mobile than the thoracic region, where, from T12 and up, ribs attach on each side at each vertebral level.
Similarly, where ribs cease to attach in the upper back, around T2 & T1, there is a transition to the cervical, comparatively more mobile, region.
These transition areas are more vulnerable to biomechanical stresses, and can be recurring trouble spots for some people.