Read about Thoracic Outlet Syndrome which will help you on your way. remember there are 3 major sites where the nerve can get trapped and this has a big influence on the problem.
You name there is some degeneration of C3-C4 and nerves from this area will innervate the intrinsic muscles of the neck which can become over active and give more compression on the affected nerves which cause arm problems. By the way does the area of armproblems (dermatome/sklerotome/myotome/joint) correspond with area of cervical rib? If not the problem might lie somewhere else. How did it start? For example carrying a backpack. General posture? (how is the muscle balance anterior posterior?)
How is the general mobility of the cervical and thoracic spine (If there is a problem at a certain level due to hyper mobility hypo mobility of segments nearby will increase the problem)
I have to stop but will come back on the subject. Cheers