Compression or traction of the nerve near shoulder. May be by a cyst arising from shoulder
This leads to nagging or severe pain just inner to shoulder in the back
If neglected may lead to weakness of muscles which move the shoulder.
In early phase conservative management releives pain. Carrying heavy back packs particularly on one side should be avoided
If this fails and MRI scan shows compression of nerve by a cyst from shoulder joint, nerve can be released by key hole surgery