Stiffness of the shoulder frequently causes shoulder pain, of which there are many causes. One must not confuse this with shoulder weakness where another person can freely move their arm. With stiffness of the shoulder, one may not be able to lift their arm, even with help.
The most common reason for shoulder stiffness is adhesive capsulitis (aka frozen shoulder). This can be very painful and often settles after a period of up to 2 years. Sub-acromial bursitis (often accompanying inflammation of the rotator cuff tendons) is another cause of shoulder stiffness. The worst point of pain is usually at the outer bony edge of the shoulder. After a fracture involving the upper arm (proximal humerus), one may experience shoulder pain and stiffness. Under the direction of the doctor or physiotherapist, rehabilitation exercises may improve the stiffness.
Arthritis of the shoulder is frequently thought to be the cause of shoulder stiffness, but is far less likely than the two previous causes. This often accompanies another condition such as long-standing tears of the rotator cuff tendons (rotator cuff arthropathy) or rheumatoid arthritis.