The rotator cuff is made up of four muscles and the tendons attached to them under the shoulder roof that lowers and raise the arm. Acromion is an extension of the shoulder blade. Subacromial bursa lies in the space between the acromion and the rotator cuff. Subacromial bursa is a sac filled with fluid that allows the rotator cuff beneath the acromion to glide smoothly when the shoulder is moved.
If the four tendons in the rotator cuff are injured, strained or a bone spur develops on the acromion, it can result in the swelling of tendons and also in the rubbing or pinching against the acromion as space between the tendons and acromion gets narrowed. The tendons get irritated when they pass through this acromial space. This is called subacromial impingement.
Subacromial impingement is also known as shoulder impingement syndrome, supraspinatus syndrome, painful arc syndrome, thrower's shoulder and swimmer's shoulder.
Repeated activity where the shoulders are moved overhead like in tennis, painting, swimming, lifting and abnormalities in bones and joints are the risk factors of subacromial impingement.
The exact cause of impingement is not explicitly known.
Subacromial impingement presents itself with the following symptoms: