What are the causes of upper back pain?

Muscles, nerves, etc: Problems or stress or disease (including myeloma or cancer) of upper back muscles, discs, facet joints, connective tissue, osteoarthritis, posture are all potential causes upper back pain.

Muscle and joint: Upper back pain most commonly from the back joints and muscles. Muscle pain can be from weak muscles (best treatment weight loss and core strengthening) or response to arthritis in the joints. Other causes are degenerated disks, fractures, tumors, infections, congenital (born with problems), scoliosis, etc.