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

• Freezing stage. Any movement of your shoulder causes pain, 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 using it becomes more difficult.
• Thawing stage. The range of motion in your shoulder begins to improve.

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

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, although it's more likely to occur in people who have diabetes or those who recently had to immobilize their shoulder for a long period, such as after surgery or an arm fracture.

Certain factors may increase your risk of developing frozen shoulder.

Age and sex

People 40 and older, particularly women, are more likely to have frozen shoulder.

Immobility or reduced mobility

People who've had prolonged immobility or reduced mobility of the shoulder are at higher risk of developing frozen shoulder. Immobility may be the result of many factors, including:

• Rotator cuff injury
• Broken arm
• Stroke
• Recovery from surgery

Systemic diseases

People who have certain diseases appear more likely to develop frozen shoulder. Diseases that might increase risk include:

• Diabetes
• Overactive thyroid (hyperthyroidism)
• Underactive thyroid (hypothyroidism)
• Cardiovascular disease
• Tuberculosis
• Parkinson's disease