Frozen shoulder is a condition where the shoulder becomes painful and hard to move. The condition is sometimes called adhesive capsulitis.
The shoulder is a joint that's made up of many parts. These parts allow you to raise, rotate, and swing your arm. The parts of a normal shoulder are:
- Humeral head. The ball at the top of the upper arm bone (humerus).
- Scapula. The shoulder blade.
- Glenoid. The shallow socket on the scapula. (The humeral head rests on the glenoid.)
- Capsule. A sheet of tough tissue that encloses the joint and joins the ball to the socket.
With frozen shoulder, the capsule becomes thick, and shrinks and pulls in (contracts). It's not clear why this happens. It may be from swelling and irritation, or from scar tissue forming. Over time, this may result in pain, stiffness, and loss of movement in the shoulder.