One source of<unk><unk>  is when the muscles underneath the<unk>  (the subscapularis muscle) atrophies. This causes the<unk>  to become very close to the rib cage, eventually causing rubbing or bumping during arm/shoulder movement. Another cause is bursitis, which is when the tissues between the shoulder blade and thoracic wall inflame. Muscle and bone abnormalities in the shoulder area can also contribute to the pain.
Snapping scapula syndrome
Milwaukee shoulder syndrome
Iliocostal friction syndrome
Facet syndrome
Dead arm syndrome
Radial tunnel syndrome
Failed back syndrome
Löfgren syndrome