In humans, the only true anatomical joints between the shoulder girdle and the axial skeleton (the spine) are the sternoclavicular joints (collar bone onto your sternum) on each side. No anatomical joint exists between each scapula and the rib cage; instead the muscular connection or physiological joint between the two permits great mobility of the shoulder girdle because the upper limb is not usually involved in weight bearing, its stability has been sacrificed in exchange for greater mobility.
The bursa is a small fluid-filled sac lined with synovial membrane and an inner capillary layer of viscous synovial fluid (similar in consistency to that of a raw egg white). It provides a cushion between the bones and tendons and/or muscles around a joint. This helps to reduce friction between the bones and allows free movement. However if this bursa becomes inflamed and contains ‘gritty’ like substances within the synovial fluid it no longer provides this cushioning but can instead cause erosion and pain. If you are dehydrated the fluid is reduced also compromising this cushioning. Both these aspects can lead to pain when moving your arms. Where does this inflammation come from? It could be caused through food intolerances or toxins within your body. This is why having a cleaner diet with alkaline forming foods and hydrating your body can alleviate this condition. Also with the proper understanding of how our body's really move, we can use our arms with more expansive movement, which is helped by applying the Alexander Technique.