There are numerous structures of the shoulder that can cause shoulder. We can break it down to a series of categories.
Rotator Cuff muscles & tendons
These injuries may be acute, chronic or acute on chronic. An acute injury may include a muscle strain with or without a partial or complete tendon tear. An acute on chronic injury will include a rotator cuff tear on a degenerative shoulder.
Over use injuries of these structure will include a tendinopathy (often seen in swimmers and throwing athletes).
Pain resulting form an instability may arise from the anterior, posterior or superior shoulder capsule & labrum. This will depend on which way your shoulder is unstable. For example if you have had a history of an anterior subluxation or dislocation pain may arise from the anterior structures.
Labral injuries arise from the cartilage of the humerous (upper arm). They can occur from an acute injury or due to age related changes.
Hypomobility may be secondary to trauma including surgery, or from injury to cervical nerve roots or brachial plexus. It may occur spontaneously in middle age – a condition called ‘idiopathic adhesive capsulitis’ or ‘frozen shoulder’
Acromioclavicular joint pathology