Frozen shoulder, medically referred to as adhesive capsulitis, is a disorder in which the shoulder capsule, the connective tissue surrounding the glenohumeral joint of the shoulder, becomes inflamed and stiff, greatly restricting motion and causing chronic pain.

Adhesive capsulitis is a painful and disabling condition that often causes great frustration for patients and caregivers due to slow recovery. Movement of the shoulder is severely restricted. Pain is usually constant, worse at night, and when the weather is colder; and along with the restricted movement can make even small tasks impossible. Certain movements or bumps can cause sudden onset of tremendous pain and cramping that can last several minutes. This condition, for which an exact cause is unknown, can last from five months to three years or more and is thought in some cases to be caused by injury or trauma to the area. It is believed that it may have an autoimmune component, with the body attacking healthy tissue in the capsule.

There is also a lack of fluid in the joint, further restricting movement. In addition to difficulty with everyday tasks, people who suffer from adhesive capsulitis usually experience problems sleeping for extended periods due to pain that is worse at night and restricted movement/positions.