What causes a frozen shoulder?

Frozen shoulder is also known as adhesive capsulitis. It is a loss of shoulder motion due to tight soft tissues around the shoulder. A restricted joint capsule is also part of the problem. Pain and limited motion usually result in loss of function as well. Muscle weakness and atrophy then develop from disuse.

The actual cause and underlying pathology behind a frozen shoulder are still unknown. People with diabetes, heart disease, and rheumatoid arthritis are at increased risk for frozen shoulder syndrome. Trauma to the shoulder can also lead to adhesive capsulitis.

There are several theories to help explain this condition. Anything that changes the way the shoulder moves and results in impaired shoulder movements can lead to shoulder capsule adhesions.

Adhesions are little areas of scar tissue that bind two areas of tissue together. When there are adhesions, the joint capsule doesn't move smoothly. Then the soft tissues around the joint start to contract and tighten up.

A cycle of pain-spasm-loss of motion-pain can develop. This keeps the individual from regaining lost motion. In addition, there is an area of extra capsular material called the capsular redundancy or axillary recess that gets stuck.

This part of the capsule is at the bottom of the shoulder joint. As the arm moves up overhead, the capsule unfolds to allow smooth gliding action. When adhesions develop within this fold, the capsule can no longer unfold and motion stops.

Again, no one is sure which comes first: loss of capsular motion and unfolding or impaired shoulder motion. Treatment for the frozen shoulder syndrome focuses on restoring both.

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