Shoulder impingement is one of the most common causes of shoulder pain and weakness. It refers to a condition in which the rotator cuff tendons are pinched during shoulder movements.
The rotator cuff is a group of tendons and muscles that connect the upper arm bone, known as the humerus, to the shoulder blade. Its function is to stabilize the shoulder and help to lift and rotate the arm. Smooth shoulder movement is facilitated by a lubricating sac (the bursa) that sits in the small space between the tendons of the rotator cuff and the outermost tip of the shoulder blade, the acromion.
During normal shoulder function the rotator cuff glides freely under the acromion. However in the presence of shoulder impingement, the space under the acromion is compromised and gliding is impaired. The rotator cuff tendons are intermittently trapped and compressed during shoulder movement. The tendons and bursa can become irritated, inflamed and swollen. Shoulder impingement can involve rotator cuff tendonitis, shoulder bursitis, and lead to partial or full thickness rotator cuff tendon tears.
Shoulder impingement is often seen in individuals engaged in athletic endeavors or occupations that involve repetitive overhead arm movements. In some cases it may arise as the result of degenerative changes including the growth of bony spurs or calcifications. Trauma, poor posture, inactivity and shoulder instability can also contribute to the development of shoulder impingement.
Common symptoms of individuals with shoulder impingement may include:
- Pain when the arms are elevated and extended above the head
- Shoulder pain that can radiate to the elbow
- Weakness of the shoulder muscles
- Pain when lying on the sore shoulder
- Difficulty reaching up behind the back
The diagnosis of shoulder impingement begins with a complete medical history followed by a physical exam. The doctor will check for the presence of inflammation and tenderness, assess the range of motion and determine if muscle strength has been affected. Imaging tests may be ordered to evaluate the integrity of the sub-acromial space, to see if there is any damage to the rotator cuff, and to rule out other conditions.
In cases of mild impingement non-surgical therapy may be helpful. This consists of activity modification, the application of ice packs, and non-steroidal anti-inflammatory medications until the symptoms subside. Typically physical therapy is recommended to restore function, reestablish a normal range of motion, and improve strength. A cortisone injection is sometimes given to reduce pain and inflammation.
In more severe cases, or when non-surgical therapy is not effective, a surgical subacromial decompression may be indicated. The goal of this minimally invasive arthroscopic procedure is to widen the subacromial space and reduce any source of rotator cuff impingement.