The four muscles that raise and lower the arm (and their respective tendons) are collectively known as the rotator cuff. This group of tissues fits neatly under the roof of the shoulder - an extension of the shoulder blade known as the acromion. However, if the cuff becomes inflamed, or some bone deformity exists in the acromion, the rotator cuff and acromion can rub against one another, causing a painful condition known as impingement. Each time the arm is raised there is a bit of rubbing on the tendons and the bursa (small fluid-filled sacs located in the shoulder to lubricate the joint and reduce friction) between the tendons and the acromion, which may cause pain and inflammation.
Image courtesy of Grant's Atlas of Anatomy
Almost everyone will experience some degree of impingement due to the day-to-day activities that we perform with the arm above shoulder level. Impingement may become a serious problem for those who continuously work with their arms raised overhead (painters, carpenters) or those who repeatedly engage in throwing activities (pitchers).
The impingement process may get worse if any condition decreases the amount of space between the acromion and the rotator cuff tendons or if bone spurs are present.
Causes and Risk Factors
Causes
- Overuse
- Wear and tear
- Arthritis
- Weak rotator cuff muscles
- Aging
