Understanding the Causes of Subacromial Impingement Syndrome

Your shoulder is made up of bones and joints that are connected together by several ligaments, tendons and muscles. With the support of these soft tissue structures, the shoulder is able to function with a wider range of motion than any other joint in the body.

The shoulder functions to predominantly support the hand in various movements that allow it to perform both high powered activities, such as throwing, and to perform other complex tasks that require more dexterity.

Often, however, adults experience shoulder pain related to stress loading and inflammation of structures identified as subacromial impingement (pain) syndrome which limits the affected shoulder’s range of motion and functional abilities. Due to the complex system controlling shoulder joint movements, a clear determination of the etiology or cause or set of causes of subacromial shoulder pain is essential for any treatment plan to be effective.




Posterior shoulder tightness: Overuse or overloading of the shoulder may cause tightness and restriction of the rotator cuff muscles and posterior capsule of the shoulder joint. This can cause the humeral head (ball) to shift upwards and potentially impinge during movements above shoulder height.

Poor shoulder blade mechanics: For proper pain free function the shoulder complex is reliant on co-ordinated movements both of the arm and the shoulder blade. Abnormal shoulder blade postures (see picture above), muscle activation patterns and timing have been shown to affect shoulder blade function and contribute to many shoulder pain states.

Shoulder instability: An inability to stabilise the shoulder joint possibly due to inherent joint laxity or inhibition of key stabilising muscles through pain or fatigue may lead to superior migration of the humeral head and impingement of the rotator cuff tendons and bursa.


Rotator cuff tendinopathy: When the rotator cuff is injured or becomes inflamed possibly due to an unaccustomed loading episode or change in training volume or speed, the shoulder may become impinged during overhead movements and irritate the bursa. Various factors have been found to be related to rotator cuff tendinopathy including chronic submaximal loading (overuse), acute unaccustomed loading, poor nutrition, poor blood supply to the affected area possibly due to smoking, age-related degeneration and trauma.

Rotator cuff tear: An injured rotator cuff can result in partial or full-thickness tears. While the majority of tears lie on the under (articular) surface of the rotator cuff, parts of the torn cuff tissue may also impinge under the acromion, causing pain during motion.


Subacromial bursitis: The acromion refers to the outermost point of the spine of the shoulder blade. Underneath the acromion is the subacromion bursa, a fluid-filled space between the acromion and rotator cuff tendons.

The rotator cuff consists of muscles and tendons that are responsible for controlling and assisting arm movements. The bursa facilitates the smooth movement of the rotator cuff.

However, when the bursa under the acromion is inflamed in a condition known as subacromial bursitis, the bursa and rotator cuff can get pinched under the acromion during overhead motions, adding to the pain radiating from the inflamed bursa. Overload, overuse or repeated irritation of the rotator cuff can lead to inflammation under the acromion.


The exact etiology of subacromial impingement (pain) syndrome is still the subject of ongoing debate although studies indicate that a combination of factors can contribute to the development of the condition. A thorough patient history usually reveals some common signs and symptoms of impingement and evidence for the effectiveness of a targeted exercise program aimed at addressing some of the key areas of dysfunction is continuing.

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