How is your upper body posture?
Head forward or shoulder rolled or hunched?
Since you have knee issues perhaps full body posture - shoulders, hips, knees, etc aligned front & side views and level across?

I'll give the thoracic outlet syndrome (TOS) link as it is a more active forum - and most likely if you had the more general RSIs , drs would be able to identify those..
so since they can't identify it yet look at TOS or pre TOS so to speak..
TOS is less well known to mainstream drs.. advanced PTs seem to be more knowledgeable of TOS.

Check the sticky threads there
http://neurotalk.psychcentral.com/forum24.html