From Jonathan Cluett, M.D.,
Your Guide to Orthopedics.
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About.com Health's Disease and Condition content is reviewed by Kate Grossman, MD

The rotator cuff is the name for the tendons that surround the shoulder joint. The rotator cuff is important in allowing the shoulder to function through a wide range of motions. In part due to the rotator cuff, the shoulder joint can move and turn through a wider range than any other joint in the body. This motion of the shoulder joint allows us to perform an amazing variety of tasks with our arms.

Unfortunately, a rotator cuff tear is not an uncommon problem, and these injuries make many routine activities difficult and painful. The rotator cuff is part of this mechanism that, when healthy functions very well, but when injured can be a difficult and frustrating problem.

What is the rotator cuff?
The rotator cuff is a group of four muscles and their tendons that wraps around the front, back, and top of the shoulder joint. Together the rotator cuff muscles help guide the shoulder through many motions, and also lend stability to the joint. The ends of the rotator cuff muscles form tendons that attach to the arm bone (humerus). It is the tendinous portion of the rotator cuff that is usually involved in a rotator cuff tear.

What is a rotator cuff tear?
A rotator cuff tear occurs when there is an injury to one of the rotator cuff tendons. Rotator cuff tears occur in many shapes and sizes, but can be thought of as a hole in one of the tendons around the shoulder joint. Like most orthopedic conditions, the most common mechanisms of a rotator cuff tear are separated into 'repetitive use' and 'traumatic injuries.'

• Repetitive Use Injury
  In repetitive use injuries to the rotator cuff, repeated activities cause damage to the rotator cuff tendons. Over time, the tendons wear thin and a rotator cuff tear can develop within the tendons. Patients with repetitive use injuries to the rotator cuff often have complaints of shoulder bursitis prior to developing a rotator cuff tear through the tendons.

• Traumatic Injuries
  Traumatic injuries to the rotator cuff are seen after events such as falling on to an outstretched hand. The traumatic event can cause a rotator cuff tear by injuring the rotator cuff tendons. This mechanism is much less common than repetitive use injuries, but when a rotator cuff tear occurs in a patient younger than 60 years old it is usually a traumatic injury.

Who is most susceptible to a rotator cuff tear?
A rotator cuff tear is seen both in the young and old, but they are much more common in the older population. Usually in younger patients, there is either a traumatic injury, or the patient is demanding unusual use of their shoulder, as seen in professional athletes.

As people age, the muscle and tendon tissue of the rotator cuff loses some elasticity, becomes more susceptible to injuries, and is often damaged while performing everyday activities. This is the reason that rotator cuff tears are more commonly seen in older patients.

How common are rotator cuff tears?
Not every rotator cuff tear causes significant pain or disability. In fact, autopsy studies have shown rotator cuff tears in up to 70 of people over the age of 80 and 30 of the population under the age of 70. Clearly, all of the people with rotator cuff tears are not complaining of painful symptoms. However, in many individuals, a rotator cuff tear can cause significant disability, and prompt diagnosis and treatment can have a profound improvement in symptoms.