shoulder pain

Hi

I'm treating a man in his sixties with unusual pain pattern. He has a 2 week history of pain inside the right shoulder that feels like scratching or like he's being clawed. No trauma - sudden onset. Only gets the pain with movement - no diurnal pattern.
The triggers for his pain are: approx. 20 extn with 20 abd (active and passive), scapular retraction (active and passive) and resisted abduction in neutral. He has very slight weakness of lat and medial rotation and abduction but nothing significant.
Cx spine and A-C joint are fine
No pain on palpation.

The right scapular is lower than the left and downwardly rotated. With repositioning of the scapula there is no pain on resisted abduction but still pain on retraction and extension with abduction. So I'm guessing that there are 2 concurrent problems - one the scapula postioning. And I'm wondering about the other.

Could it be instability?

You're suggestions would be welcome - both for what it could be and treatment options.
Thanks