What freezes in frozen shoulder?

Shoulder capsule: In frozen shoulder (or adhesive capsulitis), the actual shoulder joint is tight. Since we do not know the actual causes or adhesive capsulitis, we have difficulty studying it. We do see a period of inflammation that causes thickening of the shoulder lining (capsule). There can also be adhesions that stick from the capsule to the surrounding shoulder. This all loosens and thins over 8-16 months.

The capsule: Frozen shoulder is also termed adhesive capsulitis. The capsule is the covering of the joint and primarily formed by ligaments. Adhesions (similar to scar tissue) often form within and just outside the capsule and cause shoulder pain and stiffness. Most cases have an unknown cause (idiopathic), but frozen shoulder is more common in diabetics, those with thyroid disease and after shoulder surgery.

Capsule: A frozen shoulder occurs when the lining of the joint, called capsule, becomes inflammed and thickened. As the capsule shortens, the shoulder gradually loses range of motion.

Frozen shoulder: The capsule or lining tissues of the glenohumeral joint.

Adhesive Capsulitis: Frozen shoulder implies that the joint lining or capsule has become inflamed, thickened, and contracted. Stretching the capsule in any direction causes pain.