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Shoulder impingement: causes, identification, treatment

This is an excerpt from Sports Injuries Guidebook by Robert Gotlin.

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Common Causes

Shoulder impingement is common in sports that involve repetitive overhead motions or throwing, such as swimming, surfing, baseball, softball, water polo, and volleyball. During normal shoulder motion, the rotator cuff and subacromial bursa travel smoothly beneath the acromion in the subacromial space (the space between the acromion and humeral head). Additionally, the subacromial bursa, a small fluid-filled sac, helps the rotator cuff travel smoothly beneath the acromion and AC joint. In shoulder impingement, however, the rotator cuff and bursa get pinched or impinged underneath the acromion during overhead activities, resulting in pain.

Several factors can contribute to shoulder impingement. Structural or anatomic abnormalities might result in a narrower subacromial space. For example, some people are born with a curved or hook-shaped acromion that narrows the subacromial space. With aging, development of AC joint arthritis and bony spurs underneath the acromion can also narrow the subacromial space. The less room there is for the rotator cuff and bursa to travel, the more likely it is that these structures get pinched during shoulder motion.

A second factor is inflammation. Overuse or repetitive irritation of the rotator cuff underneath the acromion can lead to inflammation and swelling of the rotator cuff tendons and overlying bursa (tendinitis and bursitis). Not only are the inflamed tendons and bursa painful, but pain is aggravated when these inflamed and swollen structures get pinched or impinged underneath the acromion during overhead motions.

A third factor is shoulder instability, especially in young athletes. If the structures of the shoulder are ineffective in stabilizing the humeral head within the socket (glenoid fossa) during overhead motions, the humeral head might migrate upward out of the socket, causing impingement. Underlying shoulder instability is likely a primary cause of impingement symptoms in young athletes.

Identification

Shoulder impingement is an extremely common condition that affects athletes of all ages. Athletes typically experience gradual pain in the front or side of the shoulder that is aggravated by reaching or overhead activities. Sometimes the pain radiates down into the upper arm. They might have decreased range of motion and subjective weakness with difficulty raising the arm overhead or behind the back. Night pain and difficulty sleeping on the affected shoulder are also common.

Repeated impingement usually leads to rotator cuff tendinitis (inflammation of the rotator cuff tendons) and bursitis (inflammation of the subacromial bursa that overlies the rotator cuff). Again, these two conditions can aggravate the impingement symptoms.

Treatment

Athletes can begin treating shoulder impingement at home. They should avoid repetitive overhead activities and other aggravating activities until pain and inflammation subside. Anti-inflammatory medications (e.g., ibuprofen) and ice might also be helpful in reducing pain and inflammation. Early in treatment, athletes should begin range-of-motion exercises to help restore normal pain-free motion; progress exercise as pain allows.

If symptoms persist despite initial treatment, formal physical therapy might be needed to assist in decreasing inflammation and pain through electrical stimulation, ultrasound, or other modalities. A cortisone injection into the subacromial bursa can be a quick, effective way to reduce pain and inflammation. Eventually, all athletes should begin a shoulder-strengthening program with particular attention to the rotator cuff muscles. This is especially important for younger athletes, in whom impingement symptoms usually involve underlying instability.

Athletes who continue to have disabling symptoms may require surgery to correct underlying structural or anatomic abnormalities causing the impingement. In older athletes, this might involve a subacromial decompression in which arthritic bone and spurs are shaved off the acromion to allow more room for the rotator cuff to travel. In younger athletes, shoulder stabilization surgery might be required to prevent impingement related to underlying instability. If shoulder impingement continues over time, the repeated inflammation and irritation of the rotator cuff might eventually cause the cuff to wear down, degenerate, and tear.

Return to Action

Most athletes improve with conservative treatment and gradually return to sport after attaining full pain-free range of motion and full strength in the muscles surrounding the affected shoulder. Return time varies from a few weeks to a few months, depending on the degree of symptoms, extent of injury, and the sport. Taping or bracing is usually not necessary when returning to play. If symptoms recur, the athlete should stop the sport or painful activity until the sport or activity is no longer painful.

To prevent recurrence of symptoms, athletes might need to limit or avoid certain movements in their sport. They might also benefit from modifying their technique. For example, a thrower might choose to throw sidearm instead of overhead, which might prevent the rotator cuff and bursa from getting impinged underneath the acromion.

This is an excerpt from Sports Injuries Guidebook.

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