How Your Spine Could Be Hurting Your Arm
Arm pain can originate from a number of reason that start in your spine. Your spinal cord is what carries the signals between your brain and your limbs, so if there is any damage on these signal pathways, your brain will be sure to let you know.
Source Wikipedia,en:Anatomography
Usually if you are experiencing arm, shoulder, or other upper body pain and suspect it originates from a back problem, you are dealing with a thoracic spine issue. Your thoracic spine is the section from the base of your neck to the middle-back. Many things could be causing your pain such as foraminal stenosis, spinal stenosis, or maybe a disc has been ruptured and is compressing a nerve.
See other more specific conditions here.