Frozen shoulder, also known as adhesive capsulitis, is a condition characterized by stiffness and pain in your shoulder joint. Signs and symptoms begin gradually, worsen over time and then resolve, usually within a two-year period.

Your risk of developing frozen shoulder increases if you've recently had to have your arm in a sling for several weeks, or if you have had surgery in which your arm was immobilized in a specific position for a prolonged period.

Treatment for frozen shoulder involves stretching exercises and, sometimes, the injection of corticosteroids and numbing drugs into the joint capsule. In a small percentage of cases, surgery may be needed to loosen the joint capsule so that it can move more freely.

Frozen shoulder typically develops slowly, and in three stages. Each of these stages can last a number of months.

• Painful stage. During this stage, pain occurs with any movement of your shoulder, and your shoulder's range of motion starts to become limited.
• Frozen stage. Pain may begin to diminish during this stage. However, your shoulder becomes stiffer, and your range of motion decreases notably.
• Thawing stage. During the thawing stage, the range of motion in your shoulder begins to improve.

For some people, the pain worsens at night, sometimes disrupting normal sleep patterns.

The bones, ligaments and tendons that make up your shoulder joint are encased in a capsule of connective tissue. Frozen shoulder occurs when this capsule thickens and tightens around the shoulder joint, restricting its movement.

Doctors aren't sure why this happens to some people and not to others, although it's more likely to occur in people who have recently experienced prolonged immobilization of their shoulder, such as after surgery or an arm fracture. Because of the high incidence of frozen shoulder in people with diabetes, there may be an autoimmune basis to the disease.