The rotator cuff is a series of four muscles that run along the shoulder blade (scapula) around the shoulder socket (glenoid) to surround and attach to the ball (humeral head) of the shoulder joint by their tendons. The muscles of the rotator cuff work to keep the humeral head centered in the socket (glenoid) as we move our arm. Injury or degeneration (wear and tear) can result in a tear of the rotator cuff tendon. Rotator cuff tears can cause weakness and rotator cuff dysfunction. Significant or massive rotator cuff tears that are left untreated can result in the humeral head migrating upward and moving closer to the acromion (roof of the shoulder joint). This abnormal position causes the cartilage covering the bony surfaces to deteriorate (arthritis), often resulting in pain and physical limitations.
There are many theories as to why this condition occurs for some patients and not others. Regardless, the pathology of arthritis and massive rotator cuff tear lead to weakness, pain, and inflammation, which cause decreased mobility and continued symptoms.