Injury and inflammation can start the process leading to adhesive capsulitis. Painful motion causes the person to stop moving the shoulder, and it gets bound down. It can also occur as a result of other conditions such as diabetes, heart disease, and lung disease.

It was once thought that changes throughout the capsule are what caused the tightness. It is true that with a frozen shoulder, there is fibroplasia throughout the capsule. Fibroplasia refers to the formation of fibrous scar tissue.

But surgeons found that by releasing just the anterior (front) part of the capsule restores shoulder motion. Further research showed that a particular protein called vimentin is what really leads to anterior contracture (tightness) of the capsule.

By releasing the anterior capsular structures, motion is restored throughout the joint for most people. Frozen shoulder can range from loss of external rotation and abduction (moving the arm away from the body) to a complete loss of all motion. More extensive surgery may be needed for more extreme cases.