Causes and Risk Factors of Shoulder Impingement

Shoulder impingement is a condition that causes pain and pinching sensation in the shoulder. It can also decrease a person’s range of motion. Anyone can get shoulder impingement, but people with certain risk factors are more likely to develop it

• Overuse. People who participate in sports that require frequent and repetitive use of the arms and shoulders, such as baseball, swimming, tennis, and football, are at higher risk of developing shoulder impingement. Additionally, those who frequently perform heavy overhead lifting, such as construction workers or movers, also have an increased risk to develop impingement.
• Curved or hooked acromion. Some people’s natural anatomy makes them more likely to develop shoulder impingement. People who have curved or hooked acromion bones typically have a smaller subacromial space than a person who has a flat acromion.¹Garving C, Jakob S, Bauer I, Nadjar R, Brunner UH. Impingement Syndrome of the Shoulder. Dtsch Arztebl Int. 2017;114(45):765-776.
• Prominent coracoid. The coracoid is a small projection from the shoulder blade. Like people who have hooked or curved acromions, some people have prominent coracoids. These people are more susceptible to another, less common type of shoulder impingement called subcoracoid impingement.
• Shoulder instability. Shoulder instability refers to when shoulder muscles, tendons, and ligaments no longer secure the shoulder joint causing pain. As a result, the shoulder is prone to partial dislocation, dislocation, and other conditions, such as shoulder impingement.²Bigliani LU, Levine WN: Subacromial impingement syndrome. J Bone Joint Surg Am. 1997;79(12):1854-1868.

  See Dislocated Shoulder Symptoms

• Previous shoulder injuries. People who have sustained injuries to the shoulder joint, such as a torn labrum, may be at risk for developing shoulder impingement in the future.

  See SLAP Tear Shoulder Injury and Treatment

• Bone spurs. Bone spurs are projections that can cause the subacromial space to narrow and become smaller. As a result, there is less room for tendons and other soft tissues, making impingement more likely.

  See What Is a Bone Spur?

• Coracoacromial ligament calcification. The coracoacromial ligament connects the acromion to the coracoid (a projection of the shoulder blade located at the front of the body). This ligament runs in a diagonal fashion over the rotator cuff in the subacromial space. Calcifications in this ligament may cause pain and contribute to tissue injury.³Kesmezacar H, Akgun I, Ogut T, Gokay S, Uzun I: The coracoacromial ligament: The morphology and relation to rotator cuff pathology. J Shoulder Elbow Surg. 2008;17(1):182-188.
• Poor posture. Posture while reading, sitting at a desk, driving, or cooking, can play a role in the development of shoulder impingement. Hunching or slumping the shoulders can cause the narrowing of the space between the acromion and rotator cuff.
• Age. Shoulder impingement is most often seen in adults over the age of 50, although it can develop at any age.

Shoulder impingement may be a symptom of more serious problems, such as a rotator cuff tear. In these cases, a person may experience other symptoms, too.

See Rotator Cuff Injuries

Primary vs. secondary shoulder impingement
A medical professional may describe a person’s condition as either “primary” or “secondary” shoulder impingement. Primary impingement refers to causes associated with underlying structural issues and conditions, including a small subacromial space or osteoarthritis. Secondary impingement refers to movement and posture related problems, such as overuse, or an injury, such as a rotator cuff tear. Whether shoulder impingement is diagnosed as primary or secondary may affect the recommended treatment.