Compression
Another cause of upper arm pain is compression in this area. There are many reasons for this problem. Either malignant or benign tumors would invade or grow in the lower spine. Over time, they might increase in size and compress the nerves, which leads to weakness and pain. Compression can also be caused by mechanical reasons. Any abnormal interaction between the brachial plexus and the bones around the upper arm, such as the cervical spinal disks, ribs, and collarbone, would trigger weakness, numbness, and pain. [2]
