This is an injury to the complex mixture of bones, muscles, ligaments and tendons which we call the shoulder.

It is characterized by growing pain, a feeling of heat, inability to sleep on that area and some weakness in the joint.

The ball and socket of the main shoulder joint are supported and protected by the several tendons and ligaments and muscles making up the rotator cuff. Amongst the tendons, providing soft support and secreting a fluid to allow easy movement, is the bursa.

The tendonitis occurs as the tendons which hold the muscles and bones together become trapped. They then become inflamed and harder to move. They also thicken as they are injured, making the trapping worse and creating more problems.

As the tendons become swollen and inflamed, the bursa is often also inflamed so that the usual lubrication is missing, which only makes the situation worse.

This is not the same as bursitis or a tear. It is known as an impingement injury because of the pinching effect seen.

There are several possible causes. There may be an injury to the shoulder which causes the inflammation to start with.

There may be excess strain put on the tendon by repeated heavy use, for example in an athlete or sports competitor. Overhead sports people such as tennis players and baseball pitchers are vulnerable.

Some people have a collar bone which has a slightly odd shape, which pinches the tendon and gives the person an inherent risk of this injury.
People with naturally weak shoulder muscles may find the ball part of the joint rides up and down a little when stressed. This will allow the tendon to be pinched by the ball part and start the inflammation.

Full diagnosis and advice on treatment should be obtained from an Orthopedic doctor.