What is frozen shoulder?
Frozen shoulder is a condition where the ball and socket joint of the shoulder appears to "freeze". This causes loss of motion with stiffness in all directions. Typically the shoulder joint is stiff and initially painful. It can often start without an apparent cause.
It occurs when a loose bag, known as a capsule, which surrounds the shoulder joint, becomes inflamed. The bag then appears to tighten or shrink. This tightening combined with the pain restricts movement in the joint and it can be described as "frozen".
There are two main types of frozen shoulder; primary and secondary.
Why does it happen?
In primary frozen shoulder, the exact cause is often not known. It is more common in people with diabetes and with a thyroid gland problem. About 15% of patients link it to a minor injury to the shoulder.
A secondary frozen shoulder can develop if the shoulder area is kept still for some time, for example, after a stroke or heart attack. It can also occur after major injury or surgery to the shoulder.
Some experts think the inflammation starts with a problem in the shoulder itself, others feel it is related to factors away from the shoulder (e.g. stiff neck, or certain diseases). Research is continuing to try and answer some of the questions surrounding the causes of frozen shoulder.
How common is it?
Frozen shoulder is most common in people between the ages of 40 and 70 and tends to occur more often in women than in men. It is estimated to affect at least one person in 50 every year. This amounts to as many as one million people. About one in ten people who develop frozen shoulder will go on to experience similar symptoms in their other shoulder. This normally happens within five to seven years of the first one. However this tends to resolve more quickly than the first.