Stiff upper back vertebrae are very commonly associated with long periods of relative immobility as happens with desk work, and with low neck pain. This is because the two areas share movement - they're only separate in name. The two areas also share muscles with many of them travelling from the neck almost down to the mid back!
And the same applies to healthy rib movements. Knowing that nearly all our ribs connect behind us to the spine, it's easier to understand why the ribs can get in trouble with twisting movements if the spine is stiff. Because limited movement in one will tend to force more movement than normal out of the other bit - resulting in a strain of the rib joint.
Sudden unexpected moves or falls in the older person can also lead to the same problem in the spinal joints and the ribs for the simple reason that there'll be less 'spring' in the older & stiffer joints.
The upper back is an area which is often neglected in terms of exercise, simply because of the fact that many exercises don't create much movement there. So our treatments often focus on getting back any lost mobility and making sure that ribs and the neck are looked at together as part of the bigger picture.