Thus it is seen in fractures, ligament injuries, bone bruises (injury to bone without a fracture), synovitis (
inflammation of the synovial membrane that lines the joints),
osteoarthritis, osteoporosis, ischemia (decreased blood flow) and tumors.
If you had a MRI of the shoulder joint, then probably ligament injuries and fractures are ruled out. Your PCP can run the basic tests like RA factor, ANA panel etc. Possibility of ischemia should be ruled out with MRA examination.