Impingement syndrome is usually recognized in three stages. 

The first stage involves tendinitis, a mild irritation of the tendons of the rotator cuff which attach to the humeral head. The rotator cuff muscle lies in this space between the humeral head and the roof of the shoulder or acromion. Overhead activities and lifting cause the space between the humeral head and acromion to pinch or "impinge" against the bursa and tendons. This often occurs because a bone spur has narrowed the space between the humeral head and acromion. 

The second stage involves permanent changes in the tendons due to the frequent irritation. The pain becomes more severe, and weakness and stiffness of the shoulder develops. Things such as reaching behind, sleeping on the affected shoulder, putting on a belt easily, and hooking a bra may be painful. There may even be pain at rest. 

When the tendons reach their maximum level of stress, they finally tear. This is the third stage of the impingement syndrome and is also known as a rotator cuff tear. The rotator cuff is a set of four tendons that attach to the humeral head and provide the main lifting, power, and stabilizing force to the shoulder. 

Treatment

Proper treatment depends of the stage in which the problem is detected and on an accurate diagnosis.

Rest

Avoid doing things that hurt or make the pain worse the next day. Avoid the activity that started the problem. This is usually overhead activity or using the arm out away from the body.
 

Ice/heat

Apply an ice bag (over a towel) to the shoulder at least twice a day. Always apply ice for 15 minutes after any activity using the arm. Heat (alternated with cold) can also soothe pain. Warm showers, hot packs, or a hot, moist towel may also help.
 

Medication

An anti-inflammatory/analgesic medication to relieve pain and inflammation may be prescribed while the body's natural healing process goes on. An injection of cortisone into the shoulder may be recommended, depending on the type of problem diagnosed.
 

Physical Therapy

When the problem is detected early, a rehabilitation program designed specifically to strengthen the shoulder muscles which have become weak and stretch the ligaments which have become tight, can often relieve the symptoms. When the problem has persisted for a longer time, allowing permanent changes to develop in the tendon, rehabilitation is more prolonged and difficult, but is still usually successful in relieving the pain. Usually surgery is not necessary with the first two stages of impingement syndrome when the rehabilitation program has been followed.
 

Surgery

When surgery is needed, the impingement can be relieved by the latest "open" or arthroscopic techniques. The pain that accompanies a tear of the rotator cuff can be diminished by physical therapy, but surgery is often required to allow a more normal return to regular activities. The surgery can be performed through the arthroscope, but usually requires the use of an "open" surgical incision, depending on the size of the tear, and other factors.