Calcific Tendonitis
What is calcific tendonitis?
Calcific tendonitis is a build-up of calcium deposits within one or more of the four tendons that meet at the top of the shoulder joint. Together these four tendons are known as the rotator cuff. The build-up of calcium deposits leads to pressure and chemical irritation in the tendon. This can be extremely painful.
The calcium deposits can also rub or irritate a small, fluid filled sac (called a bursa), located between the bone on the top of the shoulder (called an acromion), and the rotator cuff tendons. The bursa is designed to enable the smooth gliding of the rotator cuff under the acromion. When irritated or inflamed it is less able to do this and movement results in pain.
In many cases, the calcific tendonitis can lead to symptoms of subacromial impingement. This happens when the calcium deposits cause rotator cuff tendons to be pinched against the acromion

Why does it happen?
We still don't know for sure why calcific tendonitis affects some people and not others. It can affect all age groups and a wide range of people who take part in a wide range of different activities.
How common is it?
Although any of the rotator cuff tendons may suffer from calcific tendonitis, it is the supraspinatus tendon that is most commonly affected. Age can play a role, as calcium deposits tend to be more common in the 30 to 50 age group. It may be related to some activities or occupations
