Impingement syndrome is a common shoulder condition seen in adults. This condition is closely related to shoulder bursitis and rotator cuff tendinitis. These conditions may occur alone or in combination.
In most parts of the body, muscles surround bones. In the shoulder, however, the muscle is surrounded by bone. If you were to tap on your shoulder, you would feel bone. This bone is called the acromion. Under that bone lies your rotator cuff muscles that control rotational shoulder movements. Under the rotator cuff muscles is your upper arm bone (or proximal humerus). In other words, the rotator cuff muscles are sandwiched between the acromion shoulder bone and the upper arm bone. This arrangement of bone/muscle/bone at the shoulder joint leads to the condition of impingement syndrome (shoulder bursitis, rotator cuff tendinitis).
When an injury to the rotator cuff muscle occurs, the muscle responds by swelling much the way an ankle does when it is sprained. However, because the rotator cuff muscle is surrounded by bone, its swelling causes a number of events to occur. The pressure within the muscle increases, resulting in compression and loss of blood flow in the small blood vessels called capillaries. When the blood flow is diminished, the muscle tissue begins to fray much like a rope. As the muscle tissue swells, it results in the classic features of a pain characterized like a toothache. Pain is aggravated by actions such as reaching up behind the back and reaching up overhead. Night pain may also result from this shoulder condition and results in sleep interruption. Initial treatment of impingement syndrome consists of resting the shoulder muscles and reducing inflammation.