Shoulder impingement is the subject of much debate amongst orthopaedic surgeons, and it is probably incompletely understood at this time. Shoulder impingement is a nonspecific term that may be used to describe one of several conditions that cause shoulder pain. The mechanism of impingement in a young athlete is not likely the same as that in an older, more sedentary patient. The cause of the pain may be bursitis (inflammation of the bursa overlying the rotator cuff), tendonitis (inflamation of the tendon), or partial or complete tearing of the rotator cuff itself. Typically, impingement is felt to be caused by pressure on one of the rotator cuff tendons that occurs as the arm is lifted. As the arm is lifted, the acromion bone and/or coracoacromial ligament rub or "impinge" on the surface of the rotator cuff. This causes pain and limits movement.
To better understand this concept, some knowledge of the anatomy of the shoulder is needed. The rotator cuff is made up of the tendons of four muscles - the supraspinatus, the infraspinatus, the subscapularis, and the teres minor. The tendons from these muscles merge together to cover the "ball" of the shoulder (head of the humerus). The rotator cuff muscles work together to lift and rotate the shoulder. Overlying the rotator cuff is the shoulder bursa--a smooth, fluid-filled sack that provides padding and lubrication between the cuff and the acromion bone. You can feel your acromion bone when you push down on the top of you shoulder laterally. To see an anatomical model of the shoulder, go to the Interactive Shoulder page and click on the anatomy button under the shoulder section.
Impingement is common in both young athletes and middle-aged people. Bursitis is probably the most common cause of impingement. When the bursa becomes inflamed, the conditon is known as bursitis. The inflamation may be caused by overuse of the arm, especially in the overhead or outstretched position. Athletes who use their arms overhead for swimming, baseball and tennis are particularly vulnerable. Those who do repetitive lifting or overhead activities such as paper hanging, construction or painting are also susceptible. Pain may also develop as the result of minor trauma or spontaneously with no apparent cause.
Spurring of the acromion bone that lies on top of the rotator cuff has also been implicated as one of the causes of shoulder pain. Often the spurring seen on x-ray actually represents abnormal calcification of one of the ligaments of the shoulder called the coracoacromial ligament. Some surgeons feel that the spur can cause compression and wear into the rotator cuff tendons when the shoulder is moved. This is called outlet impingement because it occurs at the shoulder outlet where the supraspinatus muscle passes beneath the acromion bone. It is not known whether the spurring is the cause or the result of other pathology in the shoulder.
Other types of impingement have been described.
Patients often do not seek treatment at an early stage, since symptoms may initially be mild. The pain typically radiates from the front of the shoulder down the side of the arm. Sudden pain may be noted with lifting and reaching movement. As the condition progresses, night pain may become especially problematic. Patients often report that they are unable to sleep on the affected side, or that they are awakened by pain when the roll onto that side during sleep. Impingement may cause local swelling and tenderness in the front of the shoulder. Athletes participating in overhead sports may have pain when throwing, swimming, serving a tennis ball, volleyball, etc. Strength and range of motion may diminish as the condition becomes worse. All movement may be limited and painful. Advanced cases may progress to become a frozen shoulder.
To diagnose shoulder impingement, an orthopaedic surgeon reviews the patient's history and symptoms, and physically examines the shoulder. He or she may take x-rays, which will sometimes show a small bone spur on the front edge of the acromion. An injection of local anesthetic into the bursa, called the impingement test, can help to confirm the diagnosis.
If symptoms persist after conservative treatment, the doctor may order an MRI (magnetic resonance imaging) study to have a better picture of the condition of the shoulder's soft tissues. An MRI can be used to identify inflammation in the bursa and rotator cuff. In some cases, partial tearing of the rotator cuff will be identified.
Initial treatment is conservative, and is is directed at reducing the inflammation in and around the shoulder and rotator cuff. The doctor may suggest that you rest and avoid overhead activities. He or she might prescribe a course of oral non-steroidal anti-inflammatory medication, such as ibuprofen, naprosyn, Aleve, Advil, etc. Stretching exercises to improve range of motion in a stiff shoulder will also help. Your doctor may recommend that you work with a physical therapist to strengthen the muscles of the shoulder girdle, neck, and back, as well as the rotator cuff. Heat and/or ice may also help. Moist heat may help the shoulder "loosen up" before stretching, while ice will reduce swelling and inflammation after exercises.
Many patients benefit from injection of local anesthetic and cortisone to the affected area. This can be an effective way to treat bursitis. Cortisone is an anti-inflammatory medication that is placed directly into the bursal space between the rotator cuff and the acromion bone. The injection itself should cause very little pain if performed by an experienced physician. Patients with diabetes should vigilant in monitoring their blood-sugar levels after receiving an injection, as cortisone may make diabetic control more difficult for a week or two after the shot.
If shoulder pain is not alleviated within a reasonable time by conservative treatment, the doctor may recommend surgery. The goal of surgery is to address the source of impingement.
The surgical procedure that is most often done for impingement is a subacromial decompression or anterior acromioplasty. This may be done arthroscopically, or through a small incision. A subacromial decompression creates more space for the rotator cuff, with the goal of allowing pain-free movement of the humeral head within the subacromial space. In most cases the front (anterior) edge of the acromion is removed along with some of the bursal tissue. The surgeon may also treat other conditions which might be identified in the shoulder at the time of surgery, such as acromioclavicular arthritis, biceps tendonitis or a partial rotator cuff tear.
The arm is typically placed in a sling after the surgery. The surgeon will provide a rehabilitation program based on the findings during surgery. This typically will include range-of-motion and strengthening exercises. The recovery time is variable, ranging from a few weeks to several months.